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Hola, mis amigos.

Soy Rhesus Macaque or some humans also call me, Rhesus Monkey.

I'm also the Old World nonhuman primates in the diverse Cercopithecidae family.

I have a significant history with humans and have aided a great deal in medical and scientific research.

Rhesus antigens found in my blood enabled doctors to identify the different human blood groups.

There are more, humans utilized me in the study of the effects of space travel on humans, as well as being the first cloned and transgenic primate.

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My scientific name is Macaca mulatta.

Here's the taxonomic hierarchy:

Kingdom: Animalia
Subkingdom: Bilateria
Infrakingdom: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostamata
Superclass: Tetrapoda
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Order: Primates
Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Cercopithecoidea
Family: Cercopithecidae
Subfamily: Cercopithecinae
Tribe: Papionini
Genus: Macaca
Species: Macaca mulatta

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Prenatal development: 5.5 months

Gestation – Gestation lasts approximately 5.5 months in rhesus macaques (146 – 180 days);

Maternal health – Infant development is significantly influenced by the health of the mother. Pregnant women who experience stress or poor health may give birth to children who exhibit permanent developmental and behavioral abnormalities.

Infancy: 0-12 months

Birth – Typically a single infant is born, usually at night. Infant weight at birth is 0.4 – 0.55 kg.

1 hour – Infant begins to suckle.

2 weeks – Mother begins introducing solid foods into the diet.

4 weeks – Infant weight is ~0.65 kg.

6 weeks – Infant is able to move independently and starts to explore away from the mother.

1 to 3.5 months – Milk composition is 4.6% fat, 1.8% protein and 7.6% sugar. Breast milk contains a higher energy density for male infants than for female infants.

4 months – Nutritional weaning begins gradually.

5 months – Infant weight is ~1 kg.

Yearlings and juveniles: 12-36 months

12 months – Yearlings weigh ~1.3 kg.

12-14 months – Nutritional weaning is complete.

Infants shouldn't be permanently weaned (from their mothers) before they are 10 to 14 months old. Early mother separation causes developmental abnormalities in infants, which can have a lifelong impact and make these animals less suitable as research models.

18 months – Juveniles usually remain close to their mother until the birth of a sibling ~1 – <2 years. Juveniles develop social skills, through sex-specific patterns of play. Their diet now resembles that of adults.

Adolescence and sexual maturity: 3-8 years

3 years – Females reach sexual maturity. Maturity may be reached sooner in captivity.

4 years – Males reach sexual maturity.

Sexual maturity – Increases in sex hormones influence secondary sexual characteristics and behavior.

Female estrous cycle is 26-29 days. Accompanied by reddening of the sexual skin on the rump and face. Peak fertility (ovulation) occurs 11-14 days after the onset of menstruation.

Males may become more aggressive and begin exploring away from the natal group.

Females may reproduce from 3-4 years of age.

Adulthood

~8 years – Males reach full body size.

Breeding – Seasonal breeders, rhesus macaques give birth in the wild at the end of the rainy season or when there is the greatest abundance of food. The timing and duration of the breeding season vary from place to place and over time (for instance, the rhesus macaque mating season on Cayo Santiago in the middle of the 1980s lasted from July to December; today, the season runs from January to June, with variations from year to year).

Mating – Macaques have numerous partners. During the breeding season, male macaques' testicles can grow up to twice as large as they normally do.

Birth – Between the ages of three and twenty, single young are born roughly every two years; higher-ranked females reproduce more frequently, earlier, and have higher infant survival rates. Birth typically takes place at night and is signalled by behavioural behaviours like touching the vagina, squatting, body trembling, tail wagging, and shifting positions frequently. One to three hours are spent during labour.

Senescence

Old age – Geriatric illnesses are rarely seen in wild populations. However, geriatric captive macaques show signs of diseases like arthritis, atherosclerosis, cataracts, gum disease, cancer, diabetes, and obesity.

<15 years – Median lifespan in the wild; <5% reach 25 years.

>25 years – Median lifespan in captivity; maximum recorded is 40 years. Females >25 years of age go through menopause.

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And now, my appearance.

General morphology:

Range in color from dusty brown to auburn with little to no fur found on our reddish-pink faces.

The hairs on the lateral sides of us are gray to brown.

The inside of the arms and legs, and the belly color pale beige to white.

Each finger and toe, five on each hand and foot, possesses a nail (unguis).

The palms of the hands and the soles of the feet are keratinized showing epidermal ridges.

The face, including the ears, has very few hairs and therefore a pinkish appearance.

We have, on average, 50 vertebrae and a wide rib cage.

Females♀ possess a pair of pectoral mammary glands.

The skin covering and surrounding the genitals is also devoid of hairs.

In males♂, the scrotum is non-pendulous and contains a pair of testes that measure 4 cm in length.

The penis♂  is normally retracted within the preputium, only extracted during mating.

Males and females are sexually dimorphic.

Our birth weight is 450 g.

Males♂ body length (without tail) is 480-635 mm, adult tail length is 203-305 mm, and weigh, on average, 7.70 kg.

Females♀ body length (without tail) is 470-531 mm, adult tail length is 189-284 mm, and an average weight of 5.34 kg.

We are quadrupedal.

Depending on the type of habitat in which we are found, can be predominantly arboreal or predominantly terrestrial.

Additionally adept swimmers, we have been seen traversing waterways as wide as one kilometer (.621 mi). We are typically found in the water when we are looking for food, fleeing from danger, maintaining body temperature, or having fun. Infants as young as two days old can already swim.

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1. Bernacky, B.J. et al.(2002) “Nonhuman primates,” Laboratory Animal Medicine, pp. 675–791. Available at: https://doi.org/10.1016/b978-012263951-7/50019-3.

2. Casteleyn, C. and Bakker, J. (2021) Anatomy of the rhesus monkey (macaca mulatta): The essentials for the biomedical researcher, IntechOpen. IntechOpen. Available at: https://www.intechopen.com/chapters/78564 (Accessed: April 16, 2023).

3. Cooper, E.B. et al. (2022) The natural history of model organisms: The rhesus macaque as a success story of the anthropocene, eLife. eLife Sciences Publications, Ltd. Available at: https://elifesciences.org/articles/78169#abstract (Accessed: April 16, 2023).

4. Itis - report: Primates (n.d.). Available at: https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180089 (Accessed: April 16, 2023).

5. Life history (n.d.) Macaques. Available at: https://macaques.nc3rs.org.uk/about-macaques/life-history (Accessed: April 16, 2023).

6. PubChem. Macaca mulatta. PubChem. https://pubchem.ncbi.nlm.nih.gov/taxonomy/9544

7. Rhesus macaque (n.d.) Wisconsin National Primate Research Center. Available at: https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-rhesus-macaque/ (Accessed: April 16, 2023).

8. Rhesus Monkey | National Geographic. Animals. 1)      https://www.nationalgeographic.com/animals/mammals/facts/rhesus-macaque#:~:text=Common%20Name%3A%20Rhesus%20Macaque,Scientific%20Name%3A%20Macaca%20mulatta

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In the late 1800s, as the theory of evolution gained more support, there was a rise in interest in studying non-human primates to learn more about human biology. The first rhesus macaque (Macaca mulatta) scientific studies were conducted during this time.

A paper on behavioural cognitive experiments was published in 1902 (Kinnaman, 1902), and the first paper was written in 1893 (Hart and Gulland, 1893) and described the "anatomy of advanced pregnancy" in rhesus macaques.

However, the Carnegie Science Institute established a breeding population of rhesus macaques in 1925 to study embryology and fertility in a species related to humans. This is when the rhesus macaque really rose to the top of non-human primate research (Wilson, 2012).

Rhesus macaques were discovered to be fairly simple to maintain and breed in captivity. They were also widely available at the time via export from colonial India. All of this increased interest in rhesus macaques as research subjects.

In 1938, the American primatologist Clarence Ray Carpenter released 409 Indian-origin rhesus macaques onto Cayo Santiago, a small island off the coast of Puerto Rico, for behavioral research (Rawlins and Kessler, 1986).

With the exception of humans, this free-ranging population of more than a thousand individuals has generated a wealth of research on the psychology and behavior of rhesus macaques that is probably unmatched by any other primate species.

Rhesus macaques are the most studied non-human primate globally and currently makeup 65% of non-human primate research subjects in the United States (Feister, 2018). Many rhesus macaque populations appear to be thriving within their natural range. The Anthropocene epoch doesn't seem to be a factor in their success, though it may be. Over the past century or so, human intervention has caused rapid changes in the rhesus macaque habitat's agricultural and urban landscape.

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We are the most common nonhuman primates used in biomedical research.

Our ancestors assisted in the discovery of the red blood cell Rh factor in 1937.

They served as the lab animals used to investigate, develop, and produce the polio vaccine in the 1950s.

They evolved into the preferred primate models for drug safety and efficacy studies in the 1970s and 1980s. The preferred model for studying the mechanisms of immunodeficiency diseases at the moment is us.

We are useful in HIV research because of our sensitivity to SIV and homology to the human MHC class I, II, and TCR genes.

We are currently the models of choice for HIV/AIDS vaccine development and study. The simian-human immunodeficiency virus (SHIV), a recombinant virus, is also widely used in research involving us.

Improved MHC typing methods and the breeding of genetically defined rhesus monkeys for use in immunological research on potential AIDS vaccine candidates are both required by these studies.

Aging, atherosclerosis, alcoholism, diabetes, cancer, and myocarditis have also been studied on us.