Rhesus Macaque (Macaca mulatta)

Characteristics

The Rhesus Macaque is brown or grey in colour and has a pink face, which is bereft of fur. Its tail is of medium length and averages between 20.7 and 22.9 cm (8.1 and 9.0 in). Adult males measure approximately 53 cm (21 in) on average and weigh about 7.7 kg (17 lb). Females are smaller, averaging 47 cm (19 in) in length and 5.3 kg (12 lb) in weight. Rhesus Macaques have on average 50 vertebrae. Their intermembral index (ratio of arms to legs) is 89%. They have dorsal scapulae and a wide rib cage. The Rhesus Macaque has 32 teeth with a dental formula of 2.1.2.3/2.1.2.3 and bilophodont molars. The upper molars have four cusps: paracone, metacone, protocone and hypocone. The lower molars also have four cusps: metaconid, protoconid, hypoconid and entoconid.

Distribution and Habitat

Rhesus Macaques are native to Northern India, Bangladesh, Pakistan, Nepal, Burma, Thailand, Afghanistan, Vietnam, Puerto Rico, southern China, and some neighbouring areas. They have the widest geographic ranges of any non human primate, occupying a great diversity of altitudes throughout Central, South and Southeast Asia. Inhabiting arid, open areas, Rhesus Macaques may be found in grasslands, woodlands and in mountainous regions up to 2,500 m (8,200 ft) in elevation. They are regular swimmers. Babies as young as a few days old can swim, and adults are known to swim over a half mile between islands, but are often found drowned in small groups where their drinking waters lie. Rhesus Macaques are noted for their tendency to move from rural to urban areas, coming to rely on handouts or refuse from humans.
The Southern and the Northern distributional limits for Rhesus and Bonnet Macaques, respectively, currently run parallel to each other in the western part of India, are separated by a large gap in the centre, and converge on the eastern coast of the peninsula to form a distribution overlap zone. This overlap region is characterized by the presence of mixed-species troops, with pure troops of both species sometimes occurring even in close proximity to one another. The range extension of Rhesus Macaque – a natural process in some areas and a direct consequence of introduction by humans in other regions – poses grave implications for the endemic and declining populations of Bonnet Macaques in southern India.

Distribution of subspecies and populations

The name "rhesus" is reminiscent of the Greek mythological king Rhesus. However, the French naturalist Jean-Baptist Audient, who applied the name to the species, stated it had no meaning.

According to Zimmermann’s first description of 1780, the Rhesus Macaque is distributed in Eastern Afghanistan, Bangladesh, Bhutan, as far east as the Brahmaputra Valley in peninsular India, Nepal and northern Pakistan. Today, this is known as the Indian rhesus macaque M. m. mulatta, which includes the morphologically similar M. rhesus villosus described by True in 1894 from Kashmir and M. m. mcmahoni described by Pocock in 1932 from Kootai, Pakistan. Several Chinese subspecies of Rhesus Macaques have been described between 1867 and 1917. The molecular differences identified among populations, however, are alone not consistent enough to conclusively define any subspecies.

The Chinese subspecies can be divided in:
M. m. mulatta is found in western and central China, in the south of Yunnan and southwest of Guangxi;M. m. lasiota (Gray, 1868), the west Chinese Rhesus Macaque, is distributed in the west of Sichuan, northwest of Yunnan, and southeast of Qinghai;[7] it is possibly synonymous with M. m. sanctijohannis (Swinhoe, 1867), if not with M. m. mulatta.
M. m. tcheliensis (Milne-Edwards, 1870), the North Chinese Rhesus Macaque, lives in the north of Henan, south of Shanxi and near Beijing. Some consider it as the most endangered subspecies.Others consider it possibly synonymous with M. m. sanctijohannis, if not with M. m. mulatta.M. m. vestita (Milne-Edwards, 1892), the Tibetan Rhesus Macaque, lives in the southeast of Tibet, northwest of Yunnan (Deqing, and perhaps including Yushu;it is possibly synonymous with M. m. sanctijohannis, if not with M. m. mulatta.
M. m. littoralis (Elliot, 1909), the South Chinese Rhesus Macaque, lives in Fujian, Zhejiang, Anhui, Jiangxi, Hunan, Hubei, Guizhou, northwest of Guangdong, north of Guangxi, northeast of Yunnan, east of Sichuan and south of Shaanxi; it is possibly synonymous with M. m. sanctijohannis, if not with M. m. mulatta.M. m. brevicaudus, also referred to as Pithecus brevicaudus (Elliot, 1913), lives on the Hainan Island and Wanshan Islands in Guangdong, and the islands near Hong Kong; it may be synonymous with M. m. mulatta.
M. m. siamica (Kloss, 1917), the Indochinese Rhesus Macaque, is distributed in Myanmar, in the North of Thailand and Vietnam, in Laos and in the Chinese provinces of Anhui, northwest Guangxi, Guizhou, Hubei, Hunan, central and eastern Sichuan, and western and south-central Yunnan; possibly synonymous with M. m. sanctijohannis, if not with M. m. mulatta.


Around the spring of 1938, a colony of Rhesus Macaques was released in the Silver River State Park in Florida by a tour boat operator known locally as "Colonel Tooey" to enhance his "Jungle Cruise". A traditional story that the monkeys were released for scenery enhancement in the Tarzan movies that were filmed at that location is false, as the only Tarzan movie filmed in the area, 1939's Tarzan Finds a Son! does not contain rhesus macaques. In addition, various colonies of Rhesus and other monkey species are speculated to be the result of zoos and wildlife parks destroyed in hurricanes, most notably Hurricane Andrew.

A notable colony of Rhesus Macaques on Morgan Island, one of the Sea Islands in the South Carolina Low country, was imported in the 1970s for use in local labs and are by all accounts thriving.

Ecology and behaviour

A roadside band of Rhesus Macaque in Rishikesh, Uttarakhand, India: Although they are infamous as urban pests, which are quick to steal not only food, but also household items, it is not certain if the pair of jeans draped over the wall on the right is their handiwork.

Rhesus Macaques are diurnal animals, and both arboreal and terrestrial. They are quadrupedal and, when on the ground, they walk digitigrade and plantigrade. They are mostly herbivorous, feeding on mainly fruit, but also eating seeds, roots, buds, bark, and cereals. They are estimated to consume around 99 different plant species in 46 families. During the monsoon season, they get much of their water from ripe and succulent fruit. Macaques living far from water sources lick dewdrops from leaves and drink rainwater accumulated in tree hollows. They have also been observed eating termites, grasshoppers, ants and beetles.When food is abundant, they are distributed in patches and forage throughout the day in their home ranges. They drink water when foraging and gather around streams and rivers. Rhesus Macaques have specialized pouch-like cheeks, allowing them to temporarily hoard their food.

In psychological research, Rhesus Macaques have demonstrated a variety of complex cognitive abilities, including the ability to make same-different judgments, understand simple rules, and monitor their own mental states. They have even been shown to demonstrate self-agency, an important type of self-awareness.


Group structure

Like other Macaques, Rhesus troops comprise a mixture of 20–200 males and females. Females may outnumber the males by a ratio of 4:1. Males and females both have separate hierarchies. Females have highly stable matrilineal hierarchies in which a female’s rank is dependent on the rank of her mother. In addition, a single group may have multiple matrilineal lines existing in a hierarchy, and a female outranks any unrelated females that rank lower than her mother. Rhesus Macaques are unusual in that the youngest females tend to outrank their older sisters. This is likely because young females are more fit and fertile. Mothers seem to prevent the older daughters from forming coalitions against her. The youngest daughter is the most dependent on the mother, and would have nothing to gain from helping her siblings in overthrowing their mother. Since each daughter had a high rank in her early years, rebelling against her mother is discouraged. Juvenile male Macaques also exist in matrilineal lines, but once they reach four to five years of age, they are driven out of their natal groups by the dominant male. Thus, adult males gain dominance by age and experience. In the group, macaques position themselves based on rank. The "central male subgroup" contains the two or three oldest and most dominant males which are codominant, along with females, their infants and juveniles. This subgroup occupies the centre of the group and determines the movements, foraging and other routines. The females of this subgroup are also the most dominant of the entire group. The farther to the periphery a subgroup is, the less dominant it is. Subgroups on the periphery of the central group are run by one dominant male which ranks lower than the central males, and maintains order in the group and communicates messages between the central and peripheral males. A subgroup of subordinate, often sub adult males occupy the very edge of the groups and have the responsibility of communicating with other macaque groups and making alarm calls.

Communication

Rhesus Macaques interact using a variety of facial expressive, vocalizations and body postures, and gestures. Perhaps the most common facial expression the Macaque makes is the "silent bared teeth" face. This is made between individuals of different social ranks with the lower ranking one giving the expression to its superior. A less dominant individual will also make a "fear grimace" accompanied by a scream to appease or redirect aggression. Another submissive behavior is the "present rump", where an individual raises its tail and exposes its genitals to the dominant one. A dominant individual will threaten another individual standing quadrupedally making a silent "open mouth stare" accompanied by the tail sticking straight. During movements, macaques will make "coos" and "grunts". These are also made during affiliative interactions and approaches before grooming. When they find rare food of high quality, Macaques will emit "warbles," "harmonic arches", or "chirps." When in threatening situations, macaques will emit a single loud, high-pitched sound called a "shrill bark" Screeches," "screams", "squeaks", "pant-threats", "growls", and "barks" are used during aggressive interactions. Infants make "geckers" during weaning conflicts.

Reproduction

Adult male Macaques try to maximize their reproductive success by entering into consort pairs with females, both in and outside the breeding period. Females prefer to mate with males that will increase the survival of their young. Thus, a consort male provides resources for his female and protects her from predators. Larger, more dominant males are more likely to provide for the females. The breeding period can last up to 11 days, and a female usually mates with four males during that time. Male Rhesus Macaques have not been observed to fight for access to sexually receptive females, although they suffer more wounds during the mating season. Female Macaques first breed when they are four years old, and reach menopause at around 25 years of age. Male Macaques generally play no role in raising the young, but do have peaceful relationships with the offspring of their consort pairs. Mothers with one or more immature daughters in addition to their infants are in contact with their infants less than those with no older immature daughters, because the mothers may pass the parenting responsibilities to her daughters. High-ranking mothers with older immature daughters also reject their infants significantly more than those without older daughters, and tend to begin mating earlier in the mating season than expected based on their dates of parturition the preceding birth season. Infants farther from the centre of the groups are more vulnerable to infanticide from outside groups. Some mothers abuse their infants, which is believed to be the result of controlling parenting styles.his adaptable species is highly promiscuous and both males and females mate with as many members of the opposite sex as possible. They travel in groups of between 8 and 180 individuals, usually with two to four times as many females as males. Breeding takes place whenever the seasons permit, with no defined period in non-seasonal areas. Females undergo a regular oestrus cycle of 26 – 29 days, but unlike many other Macaques, the genital region swells and darkens in colour only slightly during the fertile period, and only in younger adult females. Gestation lasts around 165 days, and females give birth to a single young or, rarely, twins. The young is fed milk for a year, first clinging to the mother’s belly, but riding on her back when older. After weaning, female juveniles may remain with the same group whereas males often disperse to another. Females become sexually mature between 2.5 and 4 years and males between 4.5 and 7 years. Females who reach ages of more than 25 years go through the menopause, eventually becoming infertile.

In science

The Rhesus Macaque is well known to science. Due to its relatively easy upkeep in captivity, wide availability and closeness to humans anatomically and physiologically, it has been used extensively in medical and biological research on human and animal health-related topics. It has given its name to the rhesus factor, one of the elements of a person's blood group, by the discoverers of the factor, Karl Landsteiner and Alexander Wiener. The Rhesus Macaque was also used in the well-known experiments on maternal deprivation carried out in the 1950s by controversial comparative psychologist Harry Harlow. Other medical breakthroughs facilitated by the use of the Rhesus Macaque include: development of the rabies, smallpox, and polio vaccines creation of drugs to manage HIV/AIDS understanding of the female reproductive cycle and development of the embryo and the propagation of embryonic stem cells.
The U.S. Army, the U.S. Air Force, and NASA launched Rhesus Macaques into outer space during the 1950s and '60s, and the Soviet/Russian space program launched them into space as recently as 1997 on the Bion missions. One of these primates ("Able"), which was launched on a suborbital spaceflight in 1959, was one of the two first living beings (along with "Miss Baker" on the same mission) to travel in space and return alive.

In January 2000, the Rhesus Macaque became the first cloned primate with the birth of Tetra. January 2001 saw the birth of ANDi, the first transgenic primate; ANDi carries foreign genes originally from a jellyfish.

Though most studies of the Rhesus Macaque are from various locations in Northern India, some knowledge of the natural behavior of the species comes from studies carried out on a colony established by the Caribbean Primate Research Centre of the University of Puerto Rico on the island of Cayo Santiago, off Puerto RicoThere are no predators on the island, and humans are not permitted to land except as part of the research programmes. The colony is provisioned to some extent, but about 50% of its food comes from natural foraging. In other more controlled settings, these macaques often enjoy Fig Newtons, and are particularly keen on "pouching" large quantities of marshmallows

Threats

Whilst the Rhesus Macaque is threatened in the wild, a large captive population is maintained around the world for use in biological, psychological and medicinal research, especially for studies into perception, learning and behaviour. In the wild, the Rhesus Macaque is a generalist with great adaptability, allowing it to make the most of changes in land use. In India they are known for crop-raiding but their status as sacred animals in the Hindu religion prevents persecution by humans . Interspecies breeding is known to occur but appears to have no effect on the offspring’s fertility, as other interspecies crosses usually do .

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