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In a future where temperatures are rising dramatically and the surface environment is becoming extremely harsh, people are forced to find new ways to survive. Technologically advanced human societies decide to use the underworld as a refuge from the threat of hot weather. This decision leads to a dramatic shift in the structure of society.

As the surface environment deteriorated, societies evolved into matriarchal societies that emphasised the superiority of maternal genes. Reproduction was given supreme value and the differentiation of genetic superiority and inferiority became the main division of society. In order to ensure the transmission of superior maternal genes, societies established a complex set of reproductive rules that incentivised qualified females, while the lower classes were denied the right to reproduce.

Genetic engineering and cloning became an integral part of society. The higher classes carefully selected and bred women with exceptional maternal qualities to ensure the prosperity of the race. Meanwhile, to cope with the hardships of underground existence, genetically inferior males were cloned and produced on a large scale to become the drudges of the underground society.

In this new social order, people not only have to cope with the threat posed by the climate crisis, but also have to face a huge shift in their own social structure and ethical concepts. This future world is full of challenges and conflicts, and adds uncertainty to the direction of human destiny.

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People with disabilities thinking about climate change

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People with disabilities thinking about climate change

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Generously and deliciously, Naomi Ortiz takes readers into the folds of life in the Sonoran Desert border zones, and shares 'a wobbly set of Crip hacks.' Ortiz uses humor, passion, and ceremony to invite us into their world.

~ Petra Kuppers, Anita Gonzalez Collegiate Professor of Performance Studies and Disability Culture and author of Gut Botany

In Rituals for Climate Change: A Crip Struggle for Ecojustice, Naomi Ortiz deftly braids rich lyrical poetry with poignant personal stories to explore eco-grief, ableism, and interdependence with nature. They write from a place of profound strength and softness; their powerful book is a restorative balm and rallying cry to coax us out of complacency and into interconnectedness. What a tender gem of a book that invites us to witness, listen, and grapple with the nuances and paradoxes of an ever-changing landscape.

~ Win-Sie Tow, writer and community organizer

Rituals for Climate Change is a meditation on listening, searching, supporting the ecosystem around us ... of what is in control, beyond control, and how to honor life. An exploration into poems sung to the land we lean on.

~ J. Davis, hydrologist

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Rituals for Climate Change: A Crip Struggle for Ecojustice

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Generously and deliciously, Naomi Ortiz takes readers into the folds of life in the Sonoran Desert border zones, and shares 'a wobbly set of Crip hacks.' Ortiz uses humor, passion, and ceremony to invite us into their world.

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Temperature-dependent sex determination ( TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. It is observed in reptiles and teleost fish, with some reports of it occurring in species of shrimp. TSD differs from the chromosomal sex-determination systems common among vertebrates. It is the most studied type of environmental sex determination (ESD). Some other conditions, e.g. density, pH, and environmental background color, are also observed to alter sex ratio, which could be classified either as temperature-dependent sex determination or temperature-dependent sex differentiation, depending on the involved mechanisms. As sex-determining mechanisms, TSD and genetic sex determination (GSD) should be considered in an equivalent manner, which can lead to reconsidering the status of fish species that are claimed to have TSD when submitted to extreme temperatures instead of the temperature experienced during development in the wild, since changes in sex ratio with temperature variation are ecologically and evolutionally relevant.

While TSD has been observed in many reptile and fish species, the genetic differences between sexes and molecular mechanisms of TSD have not been determined. The cortisol-mediated pathway and epigenetic regulatory pathway are thought to be the potential mechanisms involved in TSD.

The eggs are affected by the temperature at which they are incubated during the middle one-third of embryonic development. This critical period of incubation is known as the thermosensitive period. The specific time of sex-commitment is known due to several authors resolving histological chronology of sex differentiation in the gonads of turtles with TSD.

The thermosensitive, or temperature-sensitive, period is the period during development when sex is irreversibly determined. It is used in reference to species with temperature-dependent sex determination, such as crocodilians and turtles. The TSP typically spans the middle third of incubation with the endpoints defined by embryonic stage when under constant temperatures. The extent of the TSP varies a little among species, and development within the oviducts must be taken into account in species where the embryo is at a relatively late stage of development on egg laying (e.g. many lizards). Temperature pulses during the thermosensitive period are often sufficient to determine sex, but after the TSP, sex is unresponsive to temperature and sex reversal is impossible.

Patterns of temperature-dependent sex determination (TSD) in reptiles. Pattern I is found in turtles, e.g. Red-eared slider turtles (Trachemys scripta), Olive Ridley sea turtles (Lepidochelys olivacea), or Painted turtles (Chrysemys picta). Pattern II has been found in American alligators (Alligator mississippiensis and Leopard geckos (Eublepharis macularius).[13]

Some reptiles use incubation temperatures to determine sex. In some species, this follows the pattern that eggs in extremely high or low temperatures become male and eggs in medium temperatures become female.[14]

Within the mechanism, two distinct patterns have been discovered and named Pattern I and Pattern II. Pattern I is further divided into IA and IB.

Pattern IA has a single transition zone, where eggs predominantly hatch males if incubated below this temperature zone, and predominantly hatch females if incubated above it. Pattern IA occurs in most turtles, with the transition between male-producing temperatures and female-producing temperatures occurring over a range of temperatures as little as 1-2 °C. Pattern IB also has a single transition zone, but females are produced below it and males above it. Pattern IB occurs in multiple fish species and the tuatara.

Pattern II has two transition zones, with males dominating at intermediate temperatures and females dominating at both extremes. Pattern II occurs in some turtles, lizards, and crocodilians. Mixed sex ratios and (more rarely) intersex individuals have been observed at or near the pivotal temperature of sex determination.

It has been proposed that essentially all modes of TSD are actually Pattern II and those that deviate from the expected female-male-female pattern are species whose viable temperature range does not allow for the extreme temperatures needed to pass the second transition zone.

The distinction between chromosomal sex-determination systems and TSD is often blurred because the sex of some species - such as the three-lined skink Bassiana duperreyi and the central bearded dragon Pogona vitticeps - is determined by sex chromosomes, but this is over-ridden by temperatures that are tolerable but extreme. Also, experiments conducted at the pivotal temperature, where temperature is equivocal in its influence, have demonstrated an underlying genetic predisposition to be one sex or the other.

Temperature-dependent sex determination was first described in Agama agama in the year 1966 by Madeleine Charnier.

A 2015 study found that hot temperatures altered the expression of the sex chromosomes in Australia's bearded dragon lizards. The lizards were female in appearance and were capable of bearing offspring, despite having the ZZ chromosomes usually associated with male lizards.

In 2018, a team of Chinese and American researchers showed that the histone H3 lysine 27 (H3K27) demethylase KDM6B (JMJD3), an epigenetic modifier, activates male development in red-eared slider turtles by binding to the promoter of the dominant male gene [DMRT1]. Knocking down the expression of this modifier at 26 °C triggers male-to-female sex reversal in most of the surviving embryos.

Research from 2020 identified the timing of gonadal commitment in the American alligator to understand the effects of estrogen-signaling in TSD. It was determined that a main factor in gonadal fate is the level of testicular genes and estrogen signaling. The study found that critical commitment in testicular development is during stage 24-26, which is later than a known TSP for promoting males in TSD. Additionally, earlier estrogen signaling induced development of parts of the ovary.

Synergism between temperature and hormones has also been identified in these systems. Administering estradiol at male-producing temperatures generates females that are physiologically identical to temperature-produced females. The reverse experiment, males produced at female temperatures, only occurs when a nonaromatizable testosterone or an aromatase inhibitor is administered, indicating that the enzyme responsible for conversion of testosterone to estradiol, aromatase, plays a role in female development. Nonetheless, the mechanisms for TSD are still relatively unknown, but in some ways, TSD resembles genetic sex determination (GSD), particularly in regards to the effects of aromatase in each process. In some fish species, aromatase is in both the ovaries of female organisms who underwent TSD and those who underwent GSD, with no less than 85% of the coding sequences of each aromatase being identical, showing that aromatase is not unique to TSD and suggesting that there must be another factor in addition to it that is also affecting TSD.

Hormones and temperature show signs of acting in the same pathway, in that less hormone is required to produce a sexual shift as the incubation conditions near the pivotal temperature. It has been proposed that temperature acts on genes coding for such steroidogenic enzymes, and testing of homologous GSD pathways has provided a genic starting point. Yet, the genetic sexual determination pathway in TSD turtles is poorly understood and the controlling mechanism for male or female commitment has not been identified.

While sex hormones have been observed to be influenced by temperature, thus potentially altering sexual phenotypes, specific genes in the gonadal differentiation pathway display temperature influenced expression. In some species, such important sex-determining genes as DMRT1 and those involved in the Wnt signalling pathway could potentially be implicated as genes which provide a mechanism (opening the door for selective forces) for the evolutionary development of TSD. Aromatase has also been shown to play a role in certain tumor development.

The adaptive significance of TSD is currently not well understood. One possible explanation that TSD is common in amniotes is phylogenetic inertia - TSD is the ancestral condition in this clade and is simply maintained in extant lineages because it is currently adaptively neutral or nearly so. Indeed, recent phylogenetic comparative analyses imply a single origin for TSD in most amniotes around 300 million years, with the re-evolution of TSD in squamates and turtles after they had independently developed GSD. Consequently, the adaptive significance of TSD in all but the most recent origins of TSD may have been obscured by the passage of deep time, with TSD potentially being maintained in many amniote clades simply because it works 'well enough' (i.e. has no overall fitness costs along the lines of the phylogenetic inertia explanation).

Other work centers on a 1977 theoretical model (the Charnov- Bull model), predicted that selection should favour TSD over chromosome-based systems when "the developmental environment differentially influences male versus female fitness"; this theoretical model was empirically validated thirty years later but the generality of this hypothesis in reptiles is questioned. This hypothesis is supported by the persistence of TSD in certain populations of spotted skink ( Niveoscincus ocellatus), a small lizard in Tasmania, where it is advantageous to have females early in the season. The warmth early in the season ensures female-biased broods that then have more time to grow and reach maturity and possibly reproduce before they experience their first winter, thereby increasing fitness of the individual.

In support of the Charnov and Bull hypothesis, Warner and Shine (2008) showed confidently that incubation temperature influences males' reproductive success differently than females in Jacky Dragon lizards (Amphibolurus muricatus) by treating the eggs with chemicals that interfere with steroid hormone biosynthesis. These chemicals block the conversion of testosterone to estradiol during development so each sex offspring can be produced at all temperatures. They found that hatching temperatures that naturally produce each sex maximized fitness of each sex, which provides the substantial empirical evidence in support of the Charnov & Bull model for reptiles.

Spencer and Janzen (2014) found further support for the Charnov-Bull model by incubating painted turtles ( Chrysemys picta) at different temperatures and measuring various characteristics indicative of fitness. The turtles were incubated at temperatures that produce solely males, both sexes, and solely females. Spencer and Janzen (2014) found that hatchlings from mixed-sex nests were less energy efficient and grew less than their same-sex counterparts incubated in single-sex producing temperatures. Hatchlings from single-sex producing temperatures also had higher first-year survivorship than the hatchlings from the temperature that produces both sexes. TSD may be advantageous and selected for in turtles, as embryo energy efficiency and hatchling size are optimized for each sex at single-sex incubation temperatures and are indicative of first-year survivorship. This suggests that natural selection would favor TSD, as TSD may enhance the fitness of offspring.

An alternative hypothesis of adaptive significance was proposed by Bulmer and Bull in 1982 and supported by the work of Pen et al. (2010). They conjectured that disruptive selection produced by variation in the environment could result in an evolutionary transition from ESD to GSD. Pen et al. (2010) addresses evolutionary divergence in SDMs via natural selection on sex ratios. Studying the spotted skink, they observed that the highland population was not affected by temperature, yet, there was a negative correlation between annual temperature and cohort sex ratios in the lowlands. The highlands are colder with a higher magnitude of annual temperature fluctuation and a shorter activity season, delaying maturity, thus GSD is favored so sex ratios are not skewed. However, in the lowlands, temperatures are more constant and a longer activity season allows for favorable conditions for TSD. They concluded that this differentiation in climate causes divergent selection on regulatory elements in the sex-determining network allowing for the emergence of sex chromosomes in the highlands.

Climate change effects

Climate change presents a unique threat in species influenced by temperature-dependent sex determination by skewing sex ratios and population decline. The warming of the habitats of species exhibiting TSD are beginning to affect their behavior and may soon start affecting their physiology. Many species (with Pattern IA and II) have begun to nest earlier and earlier in the year to preserve the sex ratio. The three traits of pivotal temperature (the temperature at which the sex ratio is 50%), maternal nest-site choice, and nesting phenology have been identified as the key traits of TSD that can change, and of these, only the pivotal temperature is significantly heritable, this would have to increase by 27 standard deviations to compensate for a 4 °C temperature increase. It is likely that climate change will outpace the ability of many TSD animals to adapt, and many will likely go extinct. However, there is evidence that during climatic extremes, changes in the sex determining mechanism itself (to GSD) are selected for, particularly in the highly-mutable turtles. It has also been proposed that sea turtles may be able to use TSD to their advantage in a warming climate. When the offspring viability is decreased due to increased temperatures, they are able to use the coadaptation between sex ratio and survivability to increase the production of female offspring. This allows sea turtles to maintain populations and could increase their resiliency to climate change.

1. Ido Pen; Tobias Uller; Barbara Feldmeyer; Anna Harts; Geoffrey M. While & Erik Wapstra (2010). "Climate-driven population divergence in sex-determining systems". . 468 (7322): 436-439. Bibcode:2010Natur.468..436P. doi:10.1038/nature09512. PMID 20981009. S2CID 4371467.

2. ^ Warner DA, Shine R (2008). "The adaptive significance of temperature-dependent sex determination in a reptile". . 451 (7178): 566-568. Bibcode:2008Natur.451..566W. doi:10.1038/nature06519. PMID 18204437. S2CID 967516.

3. ^ Bachtrog, Doris; Mank, Judith E.; Peichel, Catherine L.; Kirkpatrick, Mark; Otto, Sarah P.; Ashman, Tia-Lynn; Hahn, Matthew W.; Kitano, Jun; Mayrose, Itay (2014-07-01). "Sex determination: why so many ways of doing it?". PLOS Biology. 12 (7): e1001899. doi:10.1371/journal.pbio.1001899. ISSN 1545-7885. PMC . PMID 24983465.

4. Ospina-Alvarez, Natalia; Piferrer, Francesc (2008-07-30). "Temperature-dependent sex determination in fish revisited: prevalence, a single sex ratio response pattern, and possible effects of climate change". PLOS ONE. 3 (7): e2837. Bibcode:2008PLoSO...3.2837O. doi:10.1371/journal.pone.0002837. ISSN 1932-6203. PMC . PMID 18665231.

5. ^ Serezeli, Ramazan (December 2017). "To what extent does temperature affect sex ratio in red cherry shrimp, neocaridina davidi? The scenario global warming to offspring sex ratio". Research Gate.

6. ^ Shen, Zhi-Gang; Wang, Han-Ping (2014-04-15). "Molecular players involved in temperature-dependent sex determination and sex differentiation in Teleost fish". Genetics Selection Evolution. 46 (1): 26. doi:10.1186/1297-9686-46-26. ISSN 1297-9686. PMC . PMID 24735220.

7. Wibbels, T.; Bull, J.J.; Crews, D. (1991). "Chronology and morphology of temperature dependent sex determination". The Journal of Experimental Zoology. 260 (3): 371-381. doi:10.1002/jez.1402600311. PMID 1744617.

8. "Temperature dependent sex determination". Turtles of the World. Archived from the original on 2009-10-08 - via ETI.

9. ^ Graves, J.A.M. (2008). "Weird animal genomes and the evolution of vertebrate sex and sex chromosomes". Annual Review of Genetics. 42: 565-86. doi:10.1146/annurev.genet.42.110807.091714. PMID 18983263.

10. ^ "Temperature-Dependent Sex Determination in Reptiles | the Embryo Project Encyclopedia".

11. ^ Wibbels, T.; Bull, J.J.; Crews, D. (1991). "Synergism between temperature and estradiol: A common pathway in turtle sex determination". The Journal of Experimental Zoology. 260 (1): 130-134. doi:10.1002/jez.1402600117. PMID 1791420.

12. ^ Duffy, T. A.; Picha, M. E.; Won, E. T.; Borski, R. J.; McElroy, A. E.; Conover, D. O. (2010). "Ontogenesis of gonadal aromatase gene expression in Atlantic silverside (Menidia menidia) populations with genetic and temperature-dependent sex determination". Journal of Experimental Zoology Part A: Ecological Genetics and Physiology. 313A (7): 421-431. doi:10.1002/jez.612. PMID 20623799.

13. ^ Graves, J.A.M. (2009). "Weird animal genomes and the evolution of human sex chromosomes". Hormone Research. 72: 15.

14. ^ Pen, Ido; Uller, Tobias; Feldmeyer, Barbara; Harts, Anna; While, Geoffrey M.; Wapstra, Erik (Nov 18, 2010). "Climate-driven population divergence in sex-determining systems". Nature. 468 (7322): 436-U262. Bibcode:2010Natur.468..436P. doi:10.1038/nature09512. PMID 20981009. S2CID 4371467.

15. ^ Hays, Graeme C.; Fossette, Sabrina; Katselidis, Kostas A.; Schofield, Gail; Gravenor, Mike B. (2010-12-01). "Breeding Periodicity for Male Sea Turtles, Operational Sex Ratios, and Implications in the Face of Climate Change". Conservation Biology. 24 (6): 1636-1643. doi:10.1111/j.1523-1739.2010.01531.x. ISSN 1523-1739. PMID 20497201. S2CID 4178364.

16. ^ Santidrián Tomillo, Pilar; Genovart, Meritxell; Paladino, Frank V.; Spotila, James R.; Oro, Daniel (2015-08-01). "Climate change overruns resilience conferred by temperature-dependent sex determination in sea turtles and threatens their survival". Global Change Biology. 21 (8): 2980-2988. Bibcode:2015GCBio..21.2980S. doi:10.1111/gcb.12918. hdl:10261/125761. ISSN 1365-2486. PMID 25929883. S2CID 39014387.

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Temperature-dependent sex determination ( TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. It is observed in reptiles and teleost fish, with some reports of it occurring in species of shrimp. TSD differs from the chromosomal sex-determination systems common among vertebrates.

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将性别平等置于气候行动的核心—— C40 城市

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Joy Belmonte 市长、Ada Colau 市长和 Alexandra Palt 阐述了确保性别平等处于气候行动核心的重要性，强调了来自 C40 城市和新的 Women4Climate 指导计划。

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2, Decrease in biodiversity; Shrinking of suitable space for humans 

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2, Decrease in biodiversity; Shrinking of suitable space for humans 

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3.Biogenetic collapse (turtles, lizards) 

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3.Biogenetic collapse (turtles, lizards) 

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1 Climate warming

2 Sea level rise

3 Decrease in biodiversity

4 Shrinking of suitable space for humans

5 Biogenetic collapse (turtles, lizards)

6 Human sperm collapse (male sperms have trouble surviving the heat)

7 Beginning to research biotechnology

8 Beginning to turn to the underworld

9 Beginning to reformulate a new class order

10 Anti-utopian society forming -J Founders -Q Inheritors -K Controller

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4. Do humans gene mutate in the heat? (eg. Gender transition?)

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4. Do humans gene mutate in the heat? (eg. Gender transition?)

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5. Creating a Livable Environment for Humanity

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5. Creating a Livable Environment for Humanity

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Male sperm can survive up to 20 degrees Celsius outside the body, and inside the body is with body temperature.

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Male sperm can survive up to 20 degrees Celsius outside the body, and inside the body is with body temperature.

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Liu

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Abstract

In specimens of semen kept at 37 degrees C sperm lose their motility and viability. If kept at 4 degrees C they retain their viability but lose their motility from so-called thermal shock. The best temperature to keep semen in order to preserve sperm motility is 20 degrees C. Loss of motility at 37 degrees C is not entirely prevented by prevention of bacterial contamination with antibiotics.

PIP: Semen specimens were obtained from 42 fertile men requesting voluntary vasectomy and stored at 4, 20, and 37 degrees C. Analysis of motility, viability under oil immersion, and pH was made after 3, 6, 12, and 18 hours. When semen was kept at 20 degrees C there was negligible deterioration in motility after 12 hours. However, there was a significant (p .01) decrease in motility in semen kept at 4 or 37 degrees, the worst being at 4 degrees. In these experiments mortility could not be restored by rewarming the semen. Viability followed motility closely at 20 and 37 degrees but at 4 degrees C viability was well preserved despite loss of motility. At the higher temperatures the motionless sperms were dead but this was not the case at 4 degrees. As expected, there was more bacterial growth at higher temperatures, mainly gram-negative bacteria such as Esch. coli and Proteus although an occasional gram positive Enterococci were identified. At 37 degrees the semen became significantly acidic (p .001). To determine the effect of bacterial growth on sperm motility, the experiment was repeated with antibiotics added. None grew any organisms and there was no fall in pH, even at 37 degrees C. Sperm kept in the presence of antibiotics retained motility at 20 and 37 degrees C better than those kept without antibiotics but there was still a significant deterioration (p .01) in the samples kept at body temperature even when bacterial growth was prevented. These studies show it is better to keep a sample of semen at room temperature (20 degrees C) during the time between ejaculation and semen analysis but do not fully explain why this is so. Specimens kept at 37 degrees C lose both motility and viability. Those kept at 4 degrees lose motility from so-called thermal shock but retain viability.

PubMed Disclaimer

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national center for biotechnology information

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The effect of temperature on the motility and viability of sperm - PubMed

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In specimens of semen kept at 37 degrees C sperm lose their motility and viability. If kept at 4 degrees C they retain their viability but lose their motility from so-called thermal shock. The best temperature to keep semen in order to preserve sperm motility is 20 degrees C.

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Zhang

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Lower temperatures produce more male hatchlings, while higher temperatures produce more female.

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Lower temperatures produce more male hatchlings, while higher temperatures produce more female.

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In addition, extreme incubation temperatures not only produce female-only hatchlings, but also result in high mortality of developing hatchlings.

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Author links open overlay panel Michael P. Jensen ¹ ⁶ ⁷ , Camryn D. Allen ¹ ² ⁶ , , , , , ,

Show more

Highlights

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We developed a novel method to estimate primary sex ratios in sea turtles

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We found extremely female-biased sex ratios in an important sea turtle population

Summary

Climate change affects species and ecosystems around the globe [ 1 ]. The impacts of rising temperature are particularly pertinent in species with temperature-dependent sex determination (TSD), where the sex of an individual is determined by incubation temperature during embryonic development [ 2 ]. In sea turtles, the proportion of female hatchlings increases with the incubation temperature. With average global temperature predicted to increase 2.6°C by 2100 [ 3 ], many sea turtle populations are in danger of high egg mortality and female-only offspring production. Unfortunately, determining the sex ratios of hatchlings at nesting beaches carries both logistical and ethical complications. However, sex ratio data obtained at foraging grounds provides information on the amalgamation of immature and adult turtles hatched from different nesting beaches over many years. Here, for the first time, we use genetic markers and a mixed-stock analysis (MSA), combined with sex determination through laparoscopy and endocrinology, to link male and female green turtles foraging in the Great Barrier Reef (GBR) to the nesting beach from which they hatched. Our results show a moderate female sex bias (65%-69% female) in turtles originating from the cooler southern GBR nesting beaches, while turtles originating from warmer northern GBR nesting beaches were extremely female-biased (99.1% of juvenile, 99.8% of subadult, and 86.8% of adult-sized turtles). Combining our results with temperature data show that the northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete feminization of this population is possible in the near future.

Keywords

temperature-dependent sex determination

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Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World

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Climate change affects species and ecosystems around the globe [1]. The impacts of rising temperature are particularly pertinent in species with tempe...

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For the community, seeking consistency and stability Here, students see the entire production process from fertilization to the birth of a baby, a process named after Garnowski, the inventor of IVF. Trained workers work meticulously on an assembly line as fertilized eggs germinate in test tubes filled with culture fluid, resulting in anywhere from eight to 96 identical newborns. When they reach adulthood, they will perform exactly the same job.
Test-tube babies are male, female, and unisex (the latter being able-bodied but infertile). According to the needs of the state, they form different grades of intelligence under the regulation of electrical appliances, in the order of five grades, namely, Alpha, Beta, Gamma, Delta, and Epsilon, and the individual grades are divided into two categories, positive and negative. Therefore, the one with the highest IQ is the positive alpha, while the one with the lowest energy is the negative epsilon. When they grow up to adulthood, they are engaged in mental work, manual labor, servant chores, and all other jobs required by society. All categories of people are thoroughly conditioned from the fetal stage, and their only response to the work assigned to them is to be content and never expect to change it. The state also forces them to take Sumo pills to avoid discontent and strong emotional changes.

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Global warming could threaten over 400 species with temperature‐dependent sex determination (TSD) worldwide, including all species of sea turtle. During embryonic development, rising temperatures might lead to the overproduction of one sex and, in turn, could bias populations’ sex ratios to an extent that threatens their persistence. If climate change predictions are correct, and biased sex ratios reduce population viability, species with TSD may go rapidly extinct unless adaptive mechanisms, whether behavioural, physiological or molecular, exist to buffer these temperature‐driven effects. Here, we summarize the discovery of the TSD phenomenon and its still elusive evolutionary significance. We then review the molecular pathways underpinning TSD in model species, along with the hormonal mechanisms that interact with temperatures to determine an individual's sex. To illustrate evolutionary mechanisms that can affect sex determination, we focus on sea turtle biology, discussing both the adaptive potential of this threatened TSD taxon, and the risks associated with conservation mismanagement.

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Abstract

Global warming could threaten over 400 species with temperature‐dependent sex determination (TSD) worldwide, including all species of sea turtle. During embryonic development, rising temperatures might lead to the overproduction of one sex and, in turn, could bias populations' sex ratios to an extent that threatens their persistence. If climate change predictions are correct, and biased sex ratios reduce population viability, species with TSD may go rapidly extinct unless adaptive mechanisms, whether behavioural, physiological or molecular, exist to buffer these temperature‐driven effects. Here, we summarize the discovery of the TSD phenomenon and its still elusive evolutionary significance. We then review the molecular pathways underpinning TSD in model species, along with the hormonal mechanisms that interact with temperatures to determine an individual's sex. To illustrate evolutionary mechanisms that can affect sex determination, we focus on sea turtle biology, discussing both the adaptive potential of this threatened TSD taxon, and the risks associated with conservation mismanagement.

Keywords: climate change, reptiles, sea turtles, sex steroid hormones, temperature‐dependent sex determination

1. INTRODUCTION

The current rate of species loss is often referred to as the sixth mass extinction event in geological history (Barnosky et al., 2011). As climate change progresses and global temperatures continue to rise rapidly, understanding how species interact with their environment has become extremely important (Hoffmann & Sgrò, 2011; Neukom et al., 2019; Stocker et al., 2013; Visser, 2008). This is particularly true for over 400 fish and reptile species that have temperature‐dependent sex determination systems (TSD). For these species, incubation temperatures differentially trigger the pathways that lead to male and female gonad development (Charnov & Bull, 1977; Deeming et al., 1988). As global warming continues, the TSD mechanism could lead to heavily skewed offspring sex ratios towards one sex, which in turn threatens populations' persistence (Eberhart‐Phillips et al., 2017; Laloë et al., 2014; Mitchell & Janzen, 2010). Whether TSD species will be able to withstand the rates of predicted temperature change and maintain viable sex ratios will depend on their adaptive potential (Eizaguirre & Baltazar‐Soares, 2014). Adaptive potential is defined as "the ability of populations/species to respond to selection by means of phenotypic or molecular changes" and interacts with population structure and demography (Eizaguirre & Baltazar‐Soares, 2014; Rey et al., 2020). Even though knowledge on the adaptive potential of TSD is essential for conservation management, it remains uncharacterized in most species, such as sea turtles (Santidrián Tomillo & Spotila, 2020).

To understand pressures on sea turtles, it is essential to acknowledge that in addition to anthropogenic climate change, they face cumulative impacts from other human‐induced stressors (Hawkes, Broderick, Coyne, et al., 2007; Hawkes, Broderick, Godfrey, et al., 2007; McMahon & Hays, 2006; Witt et al., 2010), such as coastal development (Kaska et al., 2013; Von Holle et al., 2019), fisheries bycatch (Fossette et al., 2014; Senko et al., 2014) and illegal harvest of both eggs and adults (Senko et al., 2014; Tomillo et al., 2008). As a consequence, many populations are already depleted or in decline, and subject to extensive conservation management plans (Hamann et al., 2010; Mortimer & Donnelly, 2008; Wallace et al., 2013). The actions to protect sea turtles from the effects of global warming are further limited by the inability to determine a neonate's sex nonlethally and the difficulty in justifying the sacrifice of individuals from endangered populations, both of which restrict TSD research in this taxon. As such, most interest in trying to quantify how sea turtles will adapt to climate change has focused on nesting behaviour such as phenological changes and site selection (Mazaris et al., 2013; Patrício et al., 2017; Refsnider, Bodensteiner, et al., 2013; Refsnider, Warner, et al., 2013; Reneker & Kamel, 2016). Similarly, most approaches to mitigate the effects of rising temperatures have involved human manipulation of nest temperatures through, for example, relocation (either in situ or in hatcheries) and shading (DeGregorio & Williard, 2011; Mrosovsky, 2006; Tuttle & Rostal, 2010). Here, we review the current knowledge and highlight the importance of the adaptive potential of TSD mechanisms, by bridging empirical research gained from TSD model species with the more practical management of wild populations of sea turtles. We chose to highlight molecular and physiological responses, which we consider to be under‐represented in sea turtle research in comparison with behavioural adjustments (Patrício et al., 2017; Reneker & Kamel, 2016). Finally, we discuss how failing to consider the adaptive potential and underlying mechanisms of TSD in sea turtles could lead to inappropriate management decisions.

2. TSD PATTERNS AND ENVIRONMENTAL COVARIATES

TSD species have no sex chromosomes. Instead, sex‐determining genes are scattered across the genomes, and male‐ or female‐determining pathways are triggered by temperature during a thermosensitive period of development (Bachtrog et al., 2014; Charnov & Bull, 1977; Shen & Wang, 2014). This mode of sexual development was first reported in the common agama lizard, Agama agama in 1966 (Charnier, 1966). It has since been confirmed as the sex‐determining mechanism of several reptile lineages, including the tuatara, crocodilians and turtles (Cree et al., 1995; Janzen & Paukstis, 1991).

Different patterns of TSD exist (Figure ). In type Ia TSD, seen in most turtle species, males develop at cooler temperatures while females are produced under warmer conditions (e.g. the painted turtle, Chrysemys picta, Bull & Vogt, 1979). In type Ib, this pattern is reversed, and males are produced at warm temperatures (e.g. the tuatara, Sphenodon punctatus, Cree et al., 1995). Finally, species with type II TSD, common to all crocodilians, produce males at intermediate temperatures and females at both hot and cold extremes (e.g. the American alligator, Alligator mississippiensis, Ferguson & Joanen, 1983; González et al., 2019). Under constant incubation temperatures, the TSD thermal response curve is described by i) a pivotal temperature, at which an equal number of embryos within a clutch develop as males and females, and ii) the range of temperatures under which either male or female offspring may be produced, known as the transitional range of temperatures (Figure ; Girondot, 1999; Mrosovsky & Pieau, 1991).

Genetic sex determination (GSD) and TSD are often considered to be mutually exclusive mechanisms, but instead should be regarded as two ends of a continuum, with environmental variation interacting with genetic mechanisms to different extents across species (Bachtrog et al., 2014; Holleley et al., 2015, 2016; Pen et al., 2010; Quinn et al., 2007, 2011). For instance, the montane lizard, Bassiana duperreyi, has heteromorphic sex chromosomes, and eggs incubated at warm temperatures, characteristic of lowland environments, produce equal numbers of male and female offspring. Yet, when eggs are incubated at cool temperatures representative of high altitude summers, the ratio is skewed towards 70% male hatchlings, suggesting that temperature can partly override genetic triggers in this species (Shine et al., 2002). In mammals, which have GSD, maternal condition can alter sex ratios (Grant, 2007; Sheldon & West, 2004; Trivers & Willard, 1973), moderated by the environmental conditions during the breeding and gestation periods (Edwards et al., 2019).

Temperature is the primary determinant of gonad differentiation in TSD species, and the thermal environment of nests varies with substrate albedo (Hays et al., 2001), shading (Refsnider, Bodensteiner, et al., 2013; Refsnider, Warner, et al., 2013) and nest depth (Telemeco et al., 2009; Santidrián Tomillo et al., 2017), which can all influence egg development. These variables differ depending on individual nest site selection and seasonality and thus introduce variation into offspring sex ratios within and among populations (Reneker & Kamel, 2016). It is also known that precipitation and humidity interact with thermal conditions and hence influence TSD. For instance, the relationship between rainfall and sex ratios has generally been attributed to the cooling effect of rain on the temperature of nesting substrate thanks to evaporative cooling (Godfrey et al., 1996; Houghton et al., 2007; Lolavar & Wyneken, 2015; Matsuzawa et al., 2002). An argument has recently also been made to suggest that humidity itself has an effect on sex ratios beyond that of temperature alone (Lolavar & Wyneken, 2017, 2020). While these studies have not yet robustly demonstrated the effect of humidity on TSD, they do illustrate several points. Firstly, temperature does not act in isolation in natural environments. Secondly, we still do not fully understand all the factors that influence sex determination in TSD species. As such, we should consider the potential for elements of the thermal response curve (e.g. the pivotal temperature and transitional range of temperatures) to vary from traditional values-either from plastic responses or as a result of adaptive evolution (Santidrián Tomillo & Spotila, 2020).

3. THE EVOLUTIONARY SIGNIFICANCE OF TSD

A comprehensive theory explaining the selective advantage of TSD still seems to evade researchers (Pen et al., 2010; Quinn et al., 2011; Sarre et al., 2004). While the random segregation of sex chromosomes in species with GSD reflects parents' equal chromosomal investment in male and female offspring, conforming to frequency‐dependent selection, no such theory exists to easily explain the evolutionary significance of TSD (Fisher, 1930). Instead, three relatively robust hypotheses for the evolution of TSD have been suggested, with varying levels of support; (i) the Charnov-Bull model of differential fitness, (ii) the "Mighty Males" hypothesis, and (iii) the phylogenetic inertia hypothesis (Charnov & Bull, 1977; Girondot & Pieau, 1999; Janzen & Phillips, 2006; Rollinson, 2019; Shine, 1999).

The Charnov-Bull model of differential fitness suggests that sex‐specific advantages are associated with particular thermal environments and that the TSD mechanism ensures the production of sexes at their optimal temperatures (Charnov & Bull, 1977). The theory requires a heterogeneous environment, in time or space, where males and females benefit from different conditions (Charnov & Bull, 1977). Sex‐specific benefits from particular thermal environments emerge through different mechanisms. For instance, incubation temperature may (i) affect fitness proxies, such as growth rate or size, (ii) correlate with future conditions that offspring will experience, or (iii) affect developmental rates and timing of emergence (Janzen & Phillips, 2006; Shine, 1999). Recently, it was suggested that sex‐specific fitness may stem from bimodal age at maturity distributions, as TSD species show greater dimorphism in this trait than GSD species (Bókony et al., 2019).

In TSD species, the effects of temperature and sex overlap, and therefore, it is challenging to disentangle their relative contributions to an individual's fitness (Rhen & Lang, 2004). This problem has generally been overcome with the use of exogenous hormone manipulation experiments, whereby a given sex is artificially forced to develop at temperatures that would not otherwise enable its production. One of the best examples of such an experiment focused on the jacky dragon, Amphibolurus muricatus (Warner & Shine, 2008). Eggs from this agamid lizard were incubated at a range of temperatures, and half of them were treated with an aromatase inhibitor that forced embryos to develop as male, regardless of their thermal environment. This manipulation decoupled the effects of sex and temperature on fitness and revealed that lifetime reproductive success was greater for males that were incubated at natural male‐producing temperatures (Warner & Shine, 2008). Importantly, hormone treatment had no effect on the morphology or survivorship of juvenile jacky dragons, indicating no effect of the treatment itself. Since this seminal study, further experiments have produced similar results across other agamid species (Steele & Warner, 2020). While this reproducibility gives weight to the Charnov-Bull hypothesis, whether these results can be extrapolated to all TSD species, and particularly long‐lived ones, remains unclear (Steele & Warner, 2020). This is because there are conflicting results among experiments testing the Charnov-Bull model (Janzen & Phillips, 2006). For instance, studies using the diamondback terrapin Malaclemys terrapin failed to find support for the Charnov-Bull model (Morjan & Janzen, 2003). As such, caution is needed when presenting the Charnov-Bull model as a universal explanation for TSD in reptiles (Janzen & Phillips, 2006).

Recently, Rollinson ( 2019) proposed an alternative theory for the evolution of TSD, referred to as the "Mighty Males" hypothesis, based on the maternal condition hypothesis described by Trivers and Willard ( 1973). The original hypothesis posits that females' lifetime reproductive success is mostly constrained by the number of gametes they produce and, as such, even lower quality female offspring produced under suboptimal conditions should not suffer a reduction in lifetime reproductive fitness. On the other hand, males' reproductive success is limited by their ability to compete for mating opportunities, and therefore, male offspring should be produced under the environmental conditions that maximize their overall fitness (Trivers & Willard, 1973). Given these constraints are related to sexual reproduction, independently of TSD, and given that temperature affects a wide range of traits such as size, developmental rate or embryonic mortality, Rollinson ( 2019) proposes that males should be produced at the temperatures that maximize the fitness potential of these traits, while females should be produced at the suboptimal extremes. As mortality increases with high temperatures, the Mighty Males hypothesis can be easily applied to type II (female-male-female) and type Ia (male-female) TSD species (Santidrián Tomillo & Spotila, 2020). On the other hand, it may not apply to type Ib (female-male) TSD species, unless evolutionary mechanisms exist that can significantly push back the upper temperature limits for mortality. Type Ib is rare in nature, existing in the tuatara and shorter‐lived squamata groups, and may require an alternative explanation.

Finally, the difficulty in determining the evolutionary significance of TSD may stem from phylogenetic inertia and the possibility its adaptive significance may no longer be detectable 300 million years after it evolved (Janzen & Krenz, 2004; Janzen & Phillips, 2006). After phylogenetically reconstructing the evolution of sex determination in over 400 species of squamata, many examples of transitions from TSD to GSD were identified, but there were no cases where this direction was reversed (Pokorná & Kratochvil, 2009). It was therefore suggested that sex chromosomes may evolve when sex‐specific genes are coupled with genes that provide a selective advantage to that sex. As the association between these genes strengthens and rates of recombination decrease, the conditions are met for sex chromosomes to evolve (Bachtrog et al., 2014; Muralidhar & Veller, 2018).

4. HERITABILITY, DEVELOPMENT AND MOLECULAR PATHWAYS OF SEX DETERMINATION

Despite very different sex determination mechanisms across vertebrate taxa, similar genetic pathways underpin the molecular foundations of gonad differentiation. This is consistent with conserved patterns of gonad development across vertebrates, with gonads being initiated as a bipotential genital ridge in both GSD and TSD species. From a developmental perspective, the genital ridge is formed from the coelomic epithelium, underlying mesenchymal cells and germ cells, which migrate into the ridge from the embryonic yolk sac (Morrish & Sinclair, 2002). As the somatic and germ cells proliferate, the genital ridge expands until the cell fate commits to developing as testes or ovaries. The differentiation of testes necessitates the development of the primary sex cords into testis cords, whereas the formation of ovaries requires the thickening of the coelomic epithelium while the primary sex cords disappear (Morrish & Sinclair, 2002). Importantly, depending on the species and the TSD pattern, the molecular mechanisms of the sex‐determining period can either end before signs of gonad differentiation appear, or may overlap with the early stages of gonad differentiation (Morrish & Sinclair, 2002).

Overall, there is no doubt about the role of temperature in sex determination of TSD species, yet individual responses, reflected in traits such as the feminization threshold of embryos, are underpinned by a genetic contribution with some levels of heritability, estimated in the painted turtle, Chrysemys picta, to be as high as h 2 = 0.35 (McGaugh et al., 2011). It is therefore not surprising that studies have focused on elucidating the molecular mechanisms of sex determination (Martínez‐Juárez & Moreno‐Mendoza, 2019). Conventionally, genes are classified based on their GSD sex‐specific pathways and probably all known mammalian sex‐determining genes have now been tested for their role in TSD (Rhen & Schroeder, 2010). A very thorough gene‐based overview can be found in Martínez‐Juárez and Moreno‐Mendoza ( 2019). In brief, the expression of genes such as Foxl2 (Forkhead box protein L2) and Rspo1 (encoding the protein R‐spondin‐1) becomes greater in the female‐determining pathway, but these are also detectable in the male cascade during early development (Elf, 2003). Furthermore, Dax1 (dosage‐sensitive sex reversal, adrenal hypoplasia critical region), Sf1 (steroidogenic factor 1) and Wnt4 (wingless‐type MMTV integration site family, member 4), all involved in female development and the repression of male traits, also appear to contribute to the sex determination of TSD species (Shoemaker & Crews, 2009). Conversely, in the male pathway, genes necessary for testicular differentiation include Sox9 (SRY‐box transcription factor 9), the anti‐Mullerian hormone ( AMH) and Dmrt1 (doublesex and Mab‐3‐related transcription factor 1). The expression of Sox9, a gene that belongs to the same HMG‐box transcription factor as Sry (sex‐determining region Y), is detectable in early gonad development and becomes restricted to the developing testis at the end of the thermosensitive period (reviewed in Rhen & Schroeder, 2010). Noteworthy, the expression of Sry remains elusive in reptiles. Dmrt1 is particularly interesting and shows temperature‐dependent sex‐specific expression that precedes gonadal sex differentiation. Dmrt1 expression changes with shifts in temperature in a sex‐specific manner and also responds to the presence of aromatase inhibitors-regulation of this gene has been shown to be necessary in order to initiate male development in Trachemys scripta (Ge et al., 2017).

While the identification of these genes follows a candidate gene approach, in more recent years studies of TSD have focused on gene discovery. Along this vein, several new candidates have emerged. A single nucleotide polymorphism in Cirbp (cold‐inducible RNA‐binding protein) was associated with transcript levels in the embryonic gonads of the snapping turtle ( Chelydra serpentina) during specification of gonad fate and hatchling sex (Rhen & Schroeder, 2017; Schroeder et al., 2016). The A allele was induced in embryos exposed to a female‐producing temperature, while expression of the C allele did not differ between female‐ and male‐producing temperatures. As such, AA homozygotes were more likely to develop ovaries than the CC homozygotes which all developed as males, with the AC heterozygotes standing at an intermediate frequency. From an ecological perspective, it is worth noting that changes in allele frequencies in Cirbp were detected at small and large geographical scales, suggesting local adaptation. Such patterns of local adaptation would be expected to result in higher pivotal temperatures in warmer regions, possibly mediated by resistance thresholds to the development of the high‐temperature sex, linked to genetic underpinnings. On the other hand, in the central bearded dragon ( Pogona vitticeps), a species in which chromosomal sex determination is overridden at high temperatures, sex‐reversed females are produced when an intron is retained in the mature transcripts from each of two Jumonji family genes, Jarid2 (Jumonji and AT‐rich interaction domain‐containing 2) and Jmjd3 (Jumonji domain‐containing 3, histone lysine demethylase). This intron retention was observed only in females that have been sex‐reversed by temperature, not in classic chromosomal females or males (Deveson et al., 2017). Similarly to Cirbp in C. serpentina, if the central bearded dragon has evolved mechanisms to regulate the overproduction of a given sex, we should be able to observe spatial and temporal variation of this intron loss in relation to temperature clines.

De novo genome sequencing has also introduced elements of gene and mechanism discovery. This has been the case with the assembly of American alligator genomes, which, combined with RNA sequencing and models of CTCF‐mediated chromatin looping, identified genomic regions that were significantly enriched for genes with female‐biased expression in developing gonads after the thermosensitive period (Rice et al., 2017). This approach demonstrated that oestrogen signalling is a major driver of female‐biased gene expression and holds promises for comparative genomics of TSD species.

Finally, a common pattern that has emerged from genomic studies is that the discovery of new TSD‐associated genes does not appear to be independent of epigenetic mechanisms. For instance, the DNA methylation dynamics of the Dmrt1 promoter region are tightly correlated with temperature and could mediate the impact of temperature on sex determination (Ge et al., 2018). In T. scripta, Ge et al. ( 2018) demonstrated how the epigenetic regulator Kdm6b demethylates the histone H3 lysine 27 ( H3K27) at the Dmrt1 promoter region, in a process that results in male sex determination. It appeared though that Kdm6b is not in itself responsive to temperature, and as such, the fundamental thermal trigger of this pathway remains unknown. Similarly, Jarid2 is a component of the master chromatin modifier polycomb repressive complex 2, and the mammalian sex‐determining factor Sry is directly regulated by an independent but closely related Jumonji family member (Deveson et al., 2017). The authors proposed that the alteration of Jarid2/ Jmjd3 function by intron retention alters the epigenetic landscape to override chromosomal sex‐determining cues, triggering sex reversal at extreme temperatures (Deveson et al., 2017).

It is difficult to predict the nature of selection exerted by global warming, as directional selection would be expected under a constant increase in temperature, but a predicted increased frequency of extreme events should result in fluctuating selection. When selection is constrained, then phenotypic plasticity may allow species to respond to their environment (Chevin et al., 2010). Indeed, while epigenetics, as mechanisms of phenotypic plasticity, may appear distant to practical conservation, their relevance has recently been framed in the light of management decisions (Rey et al., 2020). Altogether, understanding the mechanisms underlying phenotypic plasticity is a valuable direction of research in conservation management. In particular, here we suggest that increased consideration of endocrinology and sex steroid hormones would benefit the conservation of TSD species.

5. PLASTICITY AND SEX STEROID HORMONES IN TSD SPECIES

Physiological plasticity includes a series of mechanisms by which organisms can match their phenotypes to their environmental conditions, for instance via the endocrine system and hormone regulation (Chevin et al., 2010; Gienapp et al., 2008; Merilä & Hendry, 2014). In the specific context of phenotype-environment matching, evolutionary theory suggests that the populations demonstrating the greatest levels of plasticity in beneficial traits might have the highest potential of persisting in the face of climate change (Meyers & Bull, 2002). This is because if the cost of plasticity is low, it will reduce the range of conditions under which extinction is inevitable (Chevin et al., 2010; Sanford & Kelly, 2011). Plasticity could thus maintain populations until adaptive evolution emerges and improves the phenotype-environment match (Lande, 2009; Reusch, 2014).

Sex steroid hormones, such as oestrogens and their precursors, androgens, interact with the molecular pathways that control gonad differentiation and are fundamental for regulating gonad development across a wide variety of taxa (spanning amphibian (Ko et al., 2008), bird (Nakabayashi et al., 1998), fish (Wang et al., 2007), mammals (Uhlenhaut et al., 2009) and reptiles (Barske & Capel, 2010)). Oestrogens repress Sox9 expression, preventing the differentiation of male gonad‐specific Sertoli cells in both GSD (mouse, Uhlenhaut et al., 2009) and TSD species ( T. scripta, Barske & Capel, 2010). Conversely, the development of the müllerian ducts, which provide the structure for female gonads, correlates with changes in oestrogens in mammals, birds and reptiles (Dodd & Wibbels, 2008). In TSD species, the oestrogen 17β‐oestradiol replicates the effect of temperature in instigating demethylation of histone H3 lysine 27 ( H3K27) at the Dmrt1 promoter region, resulting in female gonad development (Ge et al., 2018). Moderating embryonic exposure to sex steroid hormones is thus likely to be an effective mechanism for conferring plasticity to the TSD thermal response curve (Bowden et al., 2000; Carter et al., 2017).

The influence of androgens and oestrogens on embryonic sex independently of temperature in TSD species has been extensively reviewed (Bowden & Paitz, 2018; Elf, 2003). To date, research exploring the relationship between steroid hormones and TSD pathways has largely focused on oestradiol, testosterone and the enzyme aromatase (Box 1). Studies began with in vitro manipulation experiments which showed that exogenous application of oestradiol produced female offspring at male‐producing temperatures (Crews et al., 1989, 1991; Wibbels et al., 1991). At the same time, the application of aromatase inhibitors such as fadrozole, which prevent the synthesis of oestradiol, has repeatedly resulted in male offspring (Rhen & Lang, 1995; Warner et al., 2017; Wibbels & Crews, 1994). Patterns of gonad development in response to exogenous hormone application have not, however, always been predictable and negative results have been reported, along with incidences where exogenous application of oestradiol unexpectedly produced male offspring (Janes et al., 2007; Warner et al., 2014).

BOX 1

Aromatase is an enzyme encoded by the Cyp19a1 gene (Strauss & FitzGerald, 2018), which is part of the cytochrome P450 superfamily. This protein is the only known enzyme to catalyse the conversion of androgens to oestrogens, a process that occurs throughout all vertebrate taxa. The P450 superfamily is an ancient lineage of genes that diverged early in the evolution of vertebrates (Boon & Simpson, 2012; Nelson et al., 2013; Simpson, 2004), with gonadal synthesis of oestrogens originating 500 mya (Lange et al., 2002). Cyp19a1 is highly conserved (Conley & Hinshelwood, 2001). In fish and reptiles, there are two aromatase isomorphs encoded by the Cyp19a1 and Cyp19b1 genes and expressed in the gonads and brain, respectively (Boon & Simpson, 2012). For most species, the majority of oestrogen biosynthesis occurs in the gonads, with biosynthesis in the brain associated with behaviour (Simpson, 2004). In comparison, a single gene encodes human aromatase, with tissue‐specific promoter regions found on exon 1 of this gene, enabling its biosynthesis to occur in a greater range of tissues (Bulun et al., 2004; Sebastian & Bulun, 2001). The upregulation of Cyp19a1 in the gonads is required for ovarian differentiation in fish (Guiguen et al., 2010), birds (Smith et al., 1997) and reptiles (Jeyasuria & Place, 1998), but not in mammals, where the knockout of Cyp19a1 does not prevent ovaries from developing (Fisher et al., 1998).

The apparent inconsistencies that are reported both between in vitro experiments and across species can be partially explained by interactions between exogenous hormones and temperature. Oestradiol and temperature produced more female embryos than would be expected by each treatment alone near the pivotal temperature of the red‐eared slider turtle T. scripta (Wibbels et al., 1991). Under extreme natural incubation temperatures (>2 °C above the 75‐year nesting site average), exogenous application of oestradiol and fadrozole had no effect on painted turtle sex ratios (Warner et al., 2017). Yet, under average seasonal conditions exogenous oestradiol produced more female offspring, and fadrozole more male offspring, than controls (Warner et al., 2017). These results suggest that temperature and hormones may have a dose‐dependent and interactive effect on sex determination pathways (Wibbels et al., 1991).

In oviparous species, a principal conduit of hormone transfer from mother to offspring is the egg yolk (Radder, 2007; Schwabl, 1993). It provides material with which to prime the reactions associated with the molecular cascades that trigger gonad differentiation. In European sea bass Dicentrarchus labrax, exposure to male‐producing temperatures results in methylation of the Cyp19a1 gene and lower aromatase expression (Navarro‐Martín et al., 2011). Similar methylation patterns are also seen in red‐eared slider turtles T. scripta (Matsumoto et al., 2016). High levels of aromatase expression will increase the biosynthesis of oestradiol from testosterone, if this substrate is available and the reaction is not inhibited (Boon & Simpson, 2012). Interestingly, the oestradiol: testosterone ratio within egg yolks at oviposition (i.e. before synthesis has occurred) varies across reptile species, having been recorded as both above and below 1, but rarely spanning an equal ratio (Radder, 2007), suggesting species‐specific regulation. Depending on species, endogenous oestradiol in yolks could act on female‐producing pathways directly, or indirectly through the aromatase synthesis of endogenous testosterone, to produce female hatchlings (Figure ). However, in loggerhead sea turtles, the ratio of oestradiol: testosterone in egg yolks can favour either hormone, or be equal (Lockley et al., 2020). In a natural experiment where temperatures were controlled among nests, equal, low concentration, oestradiol: testosterone ratios produced male offspring, which the authors theorize is due to product‐feedback inhibition of aromatase (Figure , Lockley et al., 2020). Such reactions will be occurring within the yolk of eggs used for exogenous application studies. The interference with natural oestradiol: testosterone ratios that could occur in these experiments might thus explain those occasions where exogenous oestradiol application has produced male offspring (Janes et al., 2007; Warner et al., 2014).

A fundamental constraint of our knowledge generated by exogenous application studies is therefore that the biological relevance of results within natural systems is extremely limited (Bowden & Paitz, 2018). Field studies are invaluable for elucidating how this mechanism interacts with environment. When clutches of painted turtles were incubated at constant temperatures of 28°C, the endogenous oestradiol: testosterone ratio within egg yolks correlated with a seasonal shift in sex ratio from 72% male to 76% female (Bowden et al., 2002). This relationship resulted in thermal reaction curves systematically changing across a nesting season, in a manner that allowed sex‐specific phenotypic matching, enhancing the production of female offspring under warm conditions (Carter et al., 2017). Such a mechanism fits directly with the Charnov-Bull differential fitness hypothesis, allowing nesting females to maximize female offspring production under temperatures that could be most beneficial to them. In addition, it is consistent with the "Mighty Males" hypothesis, favouring the production of female offspring under warm conditions that may increase mortality rates. This mechanism, however, could accelerate the rate of female production as temperatures rise and may therefore represent an example of evolutionary suicide (Bowden et al., 2000).

6. TEMPERATURE‐DEPENDENT SEX DETERMINATION AND SEA TURTLES

We have considered the many molecular pathways that contribute to the formation of gonads in TSD species, and outlined how sex steroid hormones can interact with temperature (Figure ). We now focus on applying this gained knowledge to sea turtles and their management, in the light of global warming. Sea turtles are type Ia TSD species (Yntema & Mrosovsky, 1982), and thus, thermal projections across the coming century suggest that offspring sex ratios will become increasingly feminized (Hawkes, Broderick, Coyne, et al., 2007; Hawkes, Broderick, Godfrey, et al., 2007; Hawkes et al., 2009; Laloë et al., 2014; Tanner et al., 2019; Witt et al., 2010; Yntema & Mrosovsky, 1982). These projections, however, do not generally account for the adaptive potential of populations (Santidrián Tomillo & Spotila, 2020).

Sea turtles demonstrate a high degree of natal philopatry to their nesting sites, often with high female fidelity and male‐mediated gene flow among mating sites (Bowen & Karl, 2007; Lee et al., 2007; Levasseur et al., 2020; Meylan et al., 1990; Stiebens et al., 2013). This strong female philopatry creates genetic structure within a rookery that is prone to the evolution of local adaptation (Baltazar‐Soares et al., 2020; Stiebens et al., 2013). Female turtles return to nest at intervals ranging from 1 to 4 years, while males return more frequently and can even remain resident to the mating grounds (Arendt et al., 2012; Hays et al., 2010; Schofield et al., 2010). Different remigration intervals between males and females result in different operational sex ratios (the ratio of sexually active males to females at the nesting site a given time) than that of adult sex ratios, which are likely to be less female‐biased than offspring sex ratios (Hays et al., 2014). While the operational sex ratio and even mating strategies (e.g. Lee & Hays, 2004) may alleviate offspring sex ratio bias, a reduction in the total number of males can have implications for populations: it can lead to reduced genetic diversity (Frankham, 2005), increase potential for inbreeding and genetic drift (Hedrick & Kalinowski, 2000) and ultimately reduce a population's fitness and its adaptive potential (Reed & Frankham, 2003).

7. TSD IN SEA TURTLES: THE BARRIERS

Little is known about TSD in sea turtles as, historically, sexing individuals has required sacrifice and histological examination of gonads (e.g. Fuentes et al., 2017; Hamann et al., 2010; Wyneken et al., 2007). As most sea turtle populations are listed on the IUCN red list, the sacrifice of hatchlings is often restricted by local authorities. Over the years, several protocols have been developed to overcome this challenge, such as quantifying the oestradiol: testosterone ratio in hatchling plasma (green sea turtle: 96.7% overall accuracy, n = 30, Xia et al., 2011, loggerhead sea turtle: 94% accuracy for males and 100% accuracy for females, n = 28, Gross et al., 1995). Along the same approach, the expression of Anti‐Müllerian Hormone ( AMH) seems to also effectively identify the sex of loggerhead sea turtle hatchlings, being expressed only in males ( n = 59, Tezak et al., 2020). These protocols will now need to be upscaled to reach a high throughput, to lead a new era of research in the study of TSD and management of sea turtles.

Until large‐scale sexing techniques are possible, our overall knowledge of TSD thermal response curves in sea turtles is limited to laboratory incubation studies with small sample sizes (Godfrey et al., 1999; Mrosovsky, 1988; Mrosovsky et al., 1992; Rimblot et al., 1985). These studies mostly identified the pivotal temperature of sea turtle populations to lie around 29°C (but see McCoy et al., 1983; Wibbels et al., 1998). In more recent years, sophisticated modelling approaches have been used to refine the characteristics of thermal response curves (Abreu‐Grobois et al., 2020), and have also quantified variation among populations (Bentley et al., 2020). However, prior to these advances, 29°C was often used as an approximate pivotal temperature to estimate sex ratios of sea turtle populations in cases where sacrificing hatchlings was not possible, using mean nest temperature during the middle third of incubation as a proxy (see Table for illustrative cases). Alternatively, studies have used the thermal response curves described specifically for the population of interest or a nearby neighbour, if these values have been reported (Table ).

TABLE 1

Species

Location

T piv (°C)

Source of T piv

Loggerhead (Laloë et al., 2014)

Cabo Verde

29, 28.8 and 29.2

Mathematical modelling-Fit three different T piv and kept 29°C

The approach of using a pivotal temperature proxy during the middle third of incubation is now widely regarded to be too oversimplified, as the thermosensitive period is dependent on development rates, which are not linearly related to temperature, particularly under variable thermal environments (Georges et al., 2005; Massey et al., 2019). Importantly, it also does not account for individual variation in, or the adaptive potential of the pivotal temperature. Other measures that correlate with sex ratio, such as incubation duration, have also been used, but estimates tend to vary dependent on the proxy used (Fuentes et al., 2017). For instance, Fuentes et al. ( 2017) demonstrated that estimating the sex ratio of natural nests using the constant temperature equivalent (which converts natural fluctuating incubation temperatures into a constant value to be compared to temperatures produced under lab conditions (Georges et al., 2005)) during the middle third of incubation, and assuming a pivotal temperature of 29.12 ° C, predicted an average sex ratio of 5.99% (95% CI: <0.1%-37%) male. This estimate increased to 9.97% (95% CI: <0.1%-86.20%) male when using incubation duration as a proxy for the same nests. While the use of proxies has contributed to our general understanding of sex ratio distributions, their reliance on pre‐existing thermal response curves makes them unable to detect real‐time deviation from such curves that might originate from different elements of the adaptive potential of sea turtles-conceivably with major consequences to past and future management decisions.

8. TSD IN SEA TURTLES: ADAPTIVE POTENTIAL

To date, attention on the impact of global warming on the sex ratios of sea turtles has largely focused on how plastic behaviours can avoid extreme sex ratio biases. Such behaviours include nest site selection (Patrício et al., 2017; Reneker & Kamel, 2016), nest depth (Refsnider, Bodensteiner, et al., 2013; Refsnider, Jeanine, et al., 2013) and phenological shifts (Mazaris et al., 2013). For instance, with rising temperatures there is evidence that nesting seasons start earlier and can be more protracted for loggerhead turtles nesting in North Carolina and Greece (Hawkes, Broderick, Coyne, et al., 2007; Hawkes, Broderick, Godfrey, et al., 2007; Mazaris et al., 2013; Patel et al., 2016; Weishampel et al., 2004). From a global perspective, there is a significant negative relationship between the dates of first nesting for populations of loggerhead sea turtles across their nesting distribution, and the sea surface temperature at the beginning of the nesting season (Mazaris et al., 2013). Despite evidence of phenological variation, the sole extent of such shifts is unlikely to be sufficient to keep up with the rate of contemporary climate change (Monsinjon et al., 2019; Telemeco et al., 2013).

Consequently, mechanisms other than behavioural adjustments may prove vitally important for sea turtles to respond to climate change. Local adaptation, which, in the case of TSD, would involve populations adjusting thermal response curves to match the changing thermal environment of their nesting sites, could be a fundamental part of this process. Patterns of local adaptation have been shown to evolve from the philopatric nature of sea turtles, as previously demonstrated for immune genes (Stiebens et al., 2013) and even feeding strategies (Cameron et al., 2019). For instance, green sea turtle hatchlings from dark sand (high temperature) beaches on Ascension Island grow faster and have higher levels of hatching success than those from nearby white sand (cool) beaches when exposed to hot artificial incubation environments (Weber et al., 2012). Interestingly, no fine‐scale adaptation of the pivotal temperature was found between turtles nesting on these two beaches in a later study, showing the context dependence of the results (Tilley et al., 2019). On the other hand, flatback turtle Natator depressus eggs at tropical latitudes in Australia have high levels of tolerance to prolonged warming exposure up to 35 °C during incubation, despite these temperatures often being lethal to other populations (Howard et al., 2015; Maulany et al., 2012). The pivotal temperatures of three genetically distinct flatback turtle populations also vary by 1.5°C, being highest in the population nesting under the warmest conditions (Bentley et al., 2020). These records of adaptation to local thermal environments provide evidence that the temperature sensitive triggers of the molecular pathways controlling sex determination can evolve (e.g. Ewert et al., 2005).

There is very little information on whether maternally derived sex steroid hormones can contribute to local adaptation, or whether they can introduce plasticity to the sea turtle TSD mechanism. This lack of attention to the evolvability of the endocrine system is unwarranted given the evidence from other TSD species (Bowden et al., 2000; Ewert et al., 2005). Experimental oestradiol treatment of olive ridley turtle eggs at male‐producing temperatures can feminize gonads (Merchant‐Larios et al., 1997), disrupt testis differentiation (Díaz‐Hernández et al., 2015), reduce cell proliferation (Díaz‐Hernández et al., 2017), delay Sox9 inhibition and delay the upregulation of FoxL2 and aromatase (Díaz‐Hernández et al., 2015). Furthermore, emerging research from a natural, in situ experiment that controlled for temperature found that the ratio of maternally derived oestradiol: testosterone in the yolk of loggerhead sea turtle eggs correlated with the sex ratio of nests independently of temperature (Lockley et al., 2020). Research that aims to evaluate the elements of the TSD mechanism that can evolve and locally adapt will be fundamental for revealing the adaptive potential of the TSD mechanism in sea turtles.

9. IMPLICATIONS FOR CONSERVATION MANAGEMENT

Global efforts dedicated to the conservation of sea turtles are extensive, with hundreds of grassroot, national and international projects working to stop the decline of populations and promote their persistence. Such work frequently focuses on the protection of nesting beaches (Fuentes et al., 2012; Hamann et al., 2010). Along with the benefits of accessibility, logistical advantages and low‐cost options, protection at this point in the life cycle can reduce threats from, for example, poaching of eggs and adult turtles (Senko et al., 2014; Tomillo et al., 2008), tidal inundation (Varela et al., 2019) and coastal development (Kaska et al., 2013; Von Holle et al., 2019).

A common conservation approach to mitigate the effects of human‐induced stressors such as coastal development and poaching is to relocate egg clutches into in situ hatcheries, where nests are protected and monitored (Mrosovsky, 2006, 2008; Pfaller et al., 2009; Pike, 2008; Tuttle & Rostal, 2010). However, these relocations should not be performed lightly, as shading, substrate properties and depth can be different from the nesting beach, and can all substantially alter the local thermal regimes (DeGregorio & Williard, 2011; Morreale et al., 1982; Tuttle & Rostal, 2010). The differences between temperatures in hatcheries and in situ sea turtle nests vary between locations. For instance, no difference in temperature was recorded during the thermosensitive period between relocated and in situ loggerhead sea turtle nests in North Carolina, but over the entire incubation period nests in the hatchery were exposed to higher overall temperatures, and hatchlings from these nests emerged sooner (DeGregorio & Williard, 2011). However, this was not observed in Georgia, where there were no significant differences in temperatures, size or incubation duration between relocated and in situ nests, but there was reduced survival in the nests that had been relocated (Tuttle & Rostal, 2010). If nest relocation is undertaken, then continuous evaluation of incubation temperatures, durations and the effects on hatchling development and fitness should always be conducted.

Crucially, if done incorrectly, relocation may interfere with natural selection for traits that will help sea turtles adjust to new temperature regimes, or reduce the effectiveness of natural buffering mechanisms, as climate change progresses (Mrosovsky, 2006; Pfaller et al., 2009). This effect may be particularly strong for these highly philopatric species, as they are the ones predicted to have evolved the strongest signature of local adaptation (Baltazar‐Soares et al., 2020; Stiebens et al., 2013). Specifically, human manipulation of nest temperatures might dampen the effects of natural selection on developing embryos, by reducing selection on the genomic mechanisms that confer thermal tolerance and a higher pivotal temperature. Alternatively, if plastic phenotype-environment matching were occurring, either in the form of maternal hormone transfer or nesting behaviour, intentionally modifying incubation conditions would cause a human‐induced thermal mismatch between the clutch and its optimal conditions.

It is thus important that if nest relocation is necessary to protect from stressors such as inundation or predation, this is done in a manner that matches the thermal environment that embryos would have experienced had eggs remained in situ. This includes taking all possible care to relocate nests to similar substrates in the vicinity of the nesting beach, in a nest cavity of the same depth and shape as originally dug by the female, with similar hydric properties. By doing this, conservationists will ensure that any behaviour is accounted for, while ensuring that unseen physiological plasticity such as hormone transfer will act in the direction of natural selection. In addition, in light of our current lack of knowledge on accurate sex ratios and adaptive potential, relocating nests with the direct intention of manipulating temperature regimes (in an attempt to mitigate against global warming itself) risks preventing populations from adapting to conditions naturally. This leaves conservationists in a position where leaving egg clutches exposed to increasing temperatures is not viable, but altering incubation conditions by reducing temperatures may also have long‐term negative consequences, whereby local adaptation is prevented or reduced. For scientists interested in TSD, focusing on developing nonlethal sexing methods that can be applied at a large scale would be extremely useful to guide such future conservation decisions.

10. CONCLUSIONS

Sea turtle conservation managers and scientists face difficult management choices as global warming progresses, and tools are still missing to make fully informed decisions about mitigation strategies. Barriers to determining neonate sex have limited our understanding of primary sex ratios in this taxon, and this knowledge gap must rapidly be overcome. It is likely that sea turtles have evolved heritable mechanisms, whether behavioural, genetic, epigenetic or physiological, to respond to climate change, but these are not currently quantified.

To inform future decisions, we must accept it is not sufficient to estimate sex ratios based on theoretical pivotal temperatures from distant populations. We must begin to monitor sex ratios in a high throughput manner to quantify the adaptive potential of these species. This will enable us to assess the thermal response curves of populations and nesting aggregations, along with their variation across time and space. How this variation is maintained is an important question in the light of climate change and the underlying mechanisms will need to be clarified.

CONFLICT OF INTEREST

The authors declare no conflicts of interest.

ACKNOWLEDGEMENTS

The authors would like to thank the NGOs they work with for sharing their concerns and asking for converting academic discussions into practical conservation recommendations. Specifically, we are grateful for our trustful interactions with Biosfera I, Caretta Caretta, Foundation Biodiversity Maio, Institute for Ocean (iMar), Projecto Vito Fogo, Projecto Vito Porto Novo, Project Biodiversity and Turtle Foundation. This work is supported by a Natural Environment Research Council grant to CE (NE/V001469/1) and Queen Mary University of London. The authors would like to thank the London NERC DTP for a studentship to ECL which primed the work reviewed here (NE/L002485/1).

Notes

Lockley EC, Eizaguirre C. Effects of global warming on species with temperature‐dependent sex determination: Bridging the gap between empirical research and management. Evol Appl. 2021;14:2361-2377. 10.1111/eva.13226 [[ PubMed] [ CrossRef] PMC free article] [ Google Scholar]

DATA AVAILABILITY STATEMENT

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

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Articles from Evolutionary Applications are provided here courtesy of Wiley-Blackwell

# data[].attributes.attachment_link.title
Effects of global warming on species with temperature‐dependent sex determination: Bridging the gap between empirical research and management

# data[].attributes.attachment_link.description
Global warming could threaten over 400 species with temperature‐dependent sex determination (TSD) worldwide, including all species of sea turtle. During embryonic development, rising temperatures might lead to the overproduction of one sex and, ...

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In his 1882 work "Going to the Theatre in the Year 2000", French illustrator Albert Robida, a pioneering sci-fi artist, envisioned a future in which the air would be filled with all manner of flying machines.

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Metropolis is a film made almost a hundred years ago, for which the director accurately predicted the state of the human world in a hundred years' time, a biting satire on the modern social environment, and for which he designed and built on the ground a modernist metropolis. We are looking at human differentiation as a result of climate change, and in doing so we are making predictions about future human existence, which may be hierarchically differentiated, based on the criterion of how future humans will procreate.

The Y chromosome is a chromosome unique to the human male, and it determines a person's sex. However, the Y chromosome has always been relatively small compared to other chromosomes and lacks mechanisms for gene repair and recombination, making it more prone to mutations and shortening. Scientists have found that in the many shortenings since human evolution, there has been a gradual decrease in the number of genes on the Y chromosome, including some genes related to reproductive and fertility functions. Could climate change be responsible for this factor.

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研究显示气候变化导致生育意愿下降。

照片：afp via getty images / ADEK BERRY

英国一个研究指出，人类因为担心气候变化而影响生育计划。

研究由伦敦大学学院（University College London）进行，分析了13个从2012到2022年的相关调查。当中涉及超过一万位来自美国、加拿大、新西兰及欧洲国家的受访者。

研究指出， 对气候变化的担心令受访者生育意愿下降， 或是打算生较少孩子。

研究分析的13个调查中， 两个于加拿大安大略省的结果都显示类似结果。 另一个于不列颠·哥伦比亚省（卑诗省）进行的定性研究， 年龄在18到25岁的七位受访女性中， 有六位指气候变化 已经 或 可能 影响她们的生育打算。

但研究亦发现，生育计划非单单与气候变化挂钩。 首席研究员迪拉斯通（Hope Dillarstone）指，人们不单担心气候变化下孩子的未来， 他们也会因生小孩对环境带来压力、家庭养育能力及政治环境等影响生育决定。

她说： 制订公共政策时， 理解大众如何因气候变化而改变生育计划将会变得十分重要。

(The Guardian, Damien Gayle, adaptation en chinois par Donna Chan)

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研究显示气候变化导致减少生育 | RCI

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研究指出， 对气候变化的担心令受访者生育意愿下降， 或是打算生较少孩子。

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The relationship between temperature and birth ratesGlobal warming has the potential to directly affect birth rates in two ways.

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The relationship between temperature and birth ratesGlobal warming has the potential to directly affect birth rates in two ways.

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First: higher temperatures may affect human sexual behaviour. After all, the higher the temperature, the more physically demanding and difficult it is for humans to perform sexual acts.

Second: Warmer temperatures can negatively affect human reproductive health, such as male sperm viability and female menstruation. This has been demonstrated on many trials and studies on mammals.

It is these two aspects that make us think that perhaps global warming may actually be a threat to human reproduction. This idea is yet to be thoroughly researched by governments and scientists.

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气候变化会影响人类的生育能力吗？|界面新闻 · 天下

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气温升高可能影响人类的性行为，也可能会对人类生殖健康产生负面影响。

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1.The key message of the film is that 'humanity must move towards a fair distribution of wealth', exploring the importance of individual initiative in driving political change critical of both capitalism and socialism.

2. The director said that the vertical cell tower "represents the inhuman indifference of the vertical self-management centre."

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This sense of sequence in playing cards fits in with the notion of time and class that we are trying to express in the story we might put on playing cards.

Playing cards it is sequential, up and down. ace is the origin, from this to 10 represents the orderly world line; JQK is the humanoid card represents the result of human's eventual survival and expresses the class high and low through the sequence.

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Impact of ambient temperature on ovarian reserve

# data[].attributes.subject
Impact of ambient temperature on ovarian reserve

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气温升高影响女性卵巢的储存能力。

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Objective

To examine the association between ambient temperature and antral follicle count (AFC), a standard measure of ovarian reserve.

Design

Prospective cohort study.

Setting

Fertility center at an academic hospital in the northeastern United States.

Patient(s)

631 women attending the Massachusetts General Hospital Fertility Center (2005-2015) who participated in the Environment and Reproductive Health Study.

Intervention(s)

Daily temperature at the women's residential address was estimated for the 90 days before their antral follicle scan using a spatially refined gridded climate data set. We evaluated the associations between temperature and AFC using Poisson regression with robust standard errors, adjusting for relative humidity, fine particulate matter exposure, age, education, smoking status, year and month of AFC, and diagnosis of diminished ovarian reserve and ovulation disorders.

Main Outcome Measure(s)

Antral follicle count as measured with transvaginal ultrasonography.

Result(s)

A 1°C increase in average maximum temperature during the 90 days before ovarian reserve testing was associated with a −1.6% (95% confidence interval [CI], −2.8, −0.4) lower AFC. Associations remained negative, but were attenuated, for average maximum temperature exposure in the 30 days (−0.9%, 95% CI, −1.8, 0.1) and 14 days (−0.8%, 95% CI, −1.6, 0.0) before AFC. The negative association between average maximum temperature and AFC was stronger in November through June than during the summer months, suggesting that timing of heat exposure and acclimatization to heat may be important factors to consider in future research.

Conclusion(s)

Exposure to higher temperatures was associated with lower ovarian reserve. These results raise concern that rising ambient temperatures worldwide may result in accelerated reproductive aging among women.

Impacto de la temperatura ambiente en la reserva ovárica.

Objetivo

Examinar la asociación entre la temperatura ambiente y el recuento de folículos antrales (AFC), un medidor estándar de reserva ovárica.

Diseño

Estudio de cohorte prospectiva.

Lugar

Centro de fertilidad en un hospital académico del noreste de Estados Unidos.

Paciente(s)

631 mujeres que acudieron al Centro de Fertilidad del Hospital General de Massachusetts (2005-20015) las cuales participaron en el estudio de Ambiente y Salud Reproductiva.

Intervención(es)

Se estimó la temperatura diaria en la dirección de residencia de las pacientes 90 días antes de la foliculometría utilizando una base de datos climática reticulada espacialmente depurada. Se evaluaron las asociaciones entre la temperatura y el AFC utilizando la regresión de Poisson con errores estándar robustos y ajustando a la humedad relativa, a la exposición a partículas finas, a la edad, al nivel educativo, al tabaquismo, al año y al mes del AFC y al diagnóstico de reserva ovárica disminuida y de alteraciones ovulatorias.

Medida(s) de resultado principal

Recuento de folículos antrales medidos mediante ecografía transvaginal.

Resultados

Un incremento de 1 °C en la temperatura máxima promedio durante los 90 días previos a la medición de la reserva ovárica se asoció con un AFC de -1.6% (intervalo de confianza del 95% [CI], -2.8,-0.4) menor. Las asociaciones permanecieron negativas, pero se atenuaron con la exposición a la temperatura máxima promedio en los 30 días (-0.9%, 95%CI, -1.8,-0.1) y 14 días (-0.8%, 95%CI, -1.6, 0.0) previos al AFC. La asociación negativa entre la temperatura máxima promedio y el AFC fue mayor de noviembre a junio que durante los meses de verano, sugiriendo que el tiempo de exposición al calor y la adaptación al calor pueden ser factores importantes a considerar en investigaciones futuras.

Conclusiones

La exposición a temperaturas más altas se asoció con una reserva ovárica menor. De estos resultados surge la preocupación relativa a que el aumento de la temperatura ambiente global pueda generar en una aceleración del envejecimiento reproductivo en las mujeres.

# data[].attributes.attachment_link.title
Impact of ambient temperature on ovarian reserve

# data[].attributes.attachment_link.description
Impacto de la temperatura ambiente en la reserva ovárica.Examinar la asociación entre la temperatura ambiente y el recuento de folículos antrales (AFC...