Gabby Jonker

Joseph Huyser

Jordan Kramer

The authors begin by discussing that Bigg’s killer whales spend more than 30% of their adult lives as post-reproductive females. There is evidence that these animals disperse from their mothers around the age of maturity. Because of this, the authors are looking into how the relationships between mother and offspring change overtime, and the opportunity for mothers to help their offspring. Nielsen examines the opportunities for females to gain inclusive fitness benefits and the potential role of kin selection in driving the evolution of post-reproductive life in Bigg’s killer whales. Nielsen et al. studies the population of Bigg’s that ranges from southeastern Alaska to northern California. The collection of photo-identification and life-history on the whales was taken from 1972 to 2020. Each whale was identified by their dorsal fins and unique markings. Sex was determined by morphological differences or genetic testing. The authors concluded that there are social associations between mother and offspring however, strength of the connection depends on the sex and age of the offspring. Sons have a stronger bond than daughters, and mothers tend to help their sons raise offspring. This increases the fitness of the mother and survival of the grandchildren. Some important conclusions are that smaller groups tend to engage in more cooperation than larger groups. This paper is important for understanding how post-reproductive life has evolved. 

In the article “Grandmothering and cognitive resources are required for the emergence of menopause and extensive post-reproductive lifespan”, the authors begin by discussing the difference in PRLs (post reproductive lifespans) between male and females of different species, specifically in humans and killer whales. They discuss multiple theories on how this came to be, such as the Grandmother Hypothesis and Embodied capital model. The article then goes deeper into how post-reproductive lives in females allows for them to help future generations grow up and raise children, and this also causes increased fertility for animals still at child-bearing age. The study used 200 simulated populations of an initial size of 1000 to deduce the effects of ecological parameters on Post-reproductive lifespans, such as how these parameters can maximize PRLs, and testing the previously mentioned Grandmother hypothesis and  embodied capital model  to see if they resulted in emergence of menopause and extended post reproductive lifespans. They found that investing in neural development promotes accumulation of skills and experience throughout life, which is beneficial to both the menopausal individual and the young.

​The article "The Evolution of Senescence and Post-Reproductive Lifespan in Guppies (Poecilia reticulata)" investigates how varying predation pressures influence the lifespan and reproductive patterns of guppy populations. In high predation areas guppies are more likely to be eaten, especially at younger ages. In low predation areas guppies have lower risk from predators, especially in early life. Researchers compared guppies from high-predation environments with those from low-predation areas, focusing on three life stages: before reproduction stage, during the reproduction stage, and the post-reproduction stage. The authors revealed that guppies in high-predation zones matured earlier and had longer reproductive lifespans, contributing to an overall increased lifespan. However, there was no significant difference in post-reproductive lifespan between the groups, suggesting that natural selection primarily affects the reproductive phase of life. This research gives evidence supporting theories that post-reproductive lifespan may be non-adaptive in species lacking social structures where post-reproductive individuals enhance the fitness of relatives.

In addition to the nonhuman primates, toothed whales, and guppies, this paper provides evidence to suggest menopause existing in honeybee societies. It begins with describing how, in queenless honeybee societies, workers can activate their own ovaries and lay unfertilized eggs. Some workers remain sterile and do not activate ovaries due to genetic and environmental conditions. Physiological age also plays a part, as activating ovaries is metabolically costly. In this study, they tested whether older workers cease reproduction by comparing ovarian development from different age cohorts as well as same-age cohorts but with a shortened life expectancy due to injury. They first indicated that the workers in different age and treatment groups had different lifespans, then focused on hypopharyngeal glands (HPGs), which produce brood food. In the control group, gland size decreased with age, but this correlation was not found in the injured group likely because they were all at least 15 days old, the age when many already would have transitioned to foraging, which leads to gland degeneration. They then focused on the number of ovarioles and ovary activation and found that older bees and injured workers showed less ovary activation. Workers with a shorter life expectancy (older and injured workers) have a higher probability of dying before their ovaries start to produce eggs, so it is possible they invest energy in helping relatives rather than reproducing themselves. As such, it is proposed that they experience a kind of menopause.

-Introduction: This will introduce our topic and provide information to allow the reader a better understanding. A video will likely be included.

-Body: This will be divided between two group members. Both will focus on providing examples of animals who experience menopause and one person will explain why most animals don't experience it while the other will focus on how it relates to cooperation.

-Conclusion: A short summary will be provided and what further directions can be made with our research found. The importance of this topic will be emphasized, and a video will also likely be added.

Menopause has developed in other species of toothed whales such as: narwhals, belugas, and short-finned pilot whales. It is theorized that toothed whales have developed menopause because of their close and lengthy contact with members of their family, however none of these species live quite as long as female orcas.

According to Aime et al. (2017), in simulations where menopause had previously developed, having an increased Post-Reproductive Lifespan leads to higher survival of grandchildren and fertility of children.

Most animals don’t go through menopause. So why do these whales? : Short Wave. (2024, March 22). NPR. https://www.npr.org/2024/03/22/1198909539/menopause-humans-whales-evolution