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The rhesus macaque ( Macaca mulatta), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies split between two groups, the Chinese-derived and the Indian-derived. Generally brown or grey in colour, it is in length with a tail and weighs . It is native to South Asia, Central Asia, and Southeast Asia and has the widest geographic range of all non-human , occupying a great diversity of altitudes and habitats.
The rhesus macaque is diurnality, arboreal, and terrestrial. It is mostly herbivorous, feeding mainly on fruit, but also eating , , buds, bark, and . Rhesus macaques living in cities also eat human food and trash. They are gregarious, with troops comprising 20–200 individuals. The social groups are matrilineal. Individuals communicate with a variety of facial expressions, vocalisations, body postures, and gestures.
As a result of the rhesus macaque's relatively easy upkeep, wide availability, and closeness to humans anatomically and physiologically, it has been used extensively in medical and biological research. It has facilitated many scientific breakthroughs including vaccines for rabies, smallpox, polio and antiretroviral medication to treat HIV/AIDS. A rhesus macaque became the first primate astronaut in 1948.
The rhesus is listed as Least Concern in the IUCN Red List.
The Chinese subspecies can be divided as follows:
The rhesus macaque has a dental formula of and bilophodont molar teeth.
The southern and the northern distributional limits for rhesus and , respectively, currently run parallel to each other in the western part of India, are separated by a large gap in the center, 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.
Kumar et al (2013) provides a summary of population distribution and habitat in India. It states that there were sightings of rhesus macaques in all surveyed habitats except semi-evergreen forests.
Around the spring of 1938, a colony of rhesus macaques was released in and around Silver Springs in Florida by a tour boat operator known locally as "Colonel Tooey" to enhance his "Jungle Cruise". Tooey had been hoping to profit from the boom in jungle adventure stories in film and print media, buying the monkeys to be attractions at his river boat tour. Tooey apparently hadn't been aware of rhesus macaques being proficient swimmers, meaning his original plan to keep the monkeys isolated to an island inside the river didn't work. The macaques nevertheless remained in the region thanks to daily feedings by Tooey and the boat tours. Tooey subsequently released additional monkeys to add to the gene pool and avoid inbreeding. The 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. Whilst this was the first colony established and the longest lasting, other colonies have since been established intentionally or accidentally. A population in Titusville, Florida, was featured at the now defunct Tropical Wonderland theme park, which coincidentally was at one time endorsed by Johnny Weissmuller, who had portrayed Tarzan in the aforementioned films. This association might have contributed to the misconception the monkeys were associated directly with the Tarzan films. This colony either escaped or was intentionally released, roaming the woods of the area for a decade. In the 1980s a trapper captured several monkeys from the Titusville population and released them in the Silver Springs area to join that population. The last printed records of monkeys in the Titusville area occurred in early 1990s, but sightings continue to this day.
Various colonies of rhesus macaque are speculated to be the result of zoos and wildlife parks destroyed in hurricanes, most notably Hurricane Andrew. A 2020 estimate put the number at 550–600 rhesus macaques living in the state; officials have caught more than 1,000 of the monkeys in the past decade. Most of the captured monkeys tested positive for herpes B virus, which leads wildlife officials to consider the animals a public health hazard. Of the three monkey species to have had any lasting presence in Florida, the other two being African and South American , the Rhesus macaques have endured the longest and are the only ones to show continual population growth. The species' adaptable nature, generalized diet, and larger size as to reduce the chance of cold stress or predator attack are thought to be reasons for their success.
Despite the risks, the macaques have continued to enjoy long-standing support from residents in Florida, strongly disagreeing with their removal. The Silver Springs colony has continued to grow in size and range, being commonly sighted in both the park grounds, the nearby city of Ocala, Florida, and the neighboring Ocala National Forest. Individuals likely originating from this colony have been seen hundreds of kilometers away, in St. Augustine, Florida and St. Petersburg, Florida. One infamous individual, named the "Mystery Monkey of Tampa Bay", evaded capture for years, inspiring social media posts and a song.
Exogenous colonies have also resulted from research activities. There is a colony of rhesus macaques on Morgan Island, one of the Sea Islands in the South Carolina Lowcountry. They were imported in the 1970s for use in the local labs. The State | Homepage Another research colony was established by the Caribbean Primate Research Center of the University of Puerto Rico on the island of Cayo Santiago, (1986). 9780887061356, State University of New York Press. ISBN 9780887061356 off of Puerto Rico. There are no predators on the island, and humans are not permitted to land, except as part of the research program. Another Puerto Rico research colony was released into the Desecheo National Wildlife Refuge in 1966. they are continuing to do ecological harm, damage crops amounting to $300,000/year and cost $1,000,000/year to manage.
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. In 2014, onlookers at a train station in Kanpur, India, documented a rhesus monkey, knocked unconscious by overhead power lines, that was revived by another rhesus that systematically administered a series of resuscitative actions.
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 center 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, of a rank lower than the central males, and he maintains order in the group, and communicates messages between the central and peripheral males. A subgroup of subordinate, often subadult, males occupy the very edge of the groups, and have the responsibility of communicating with other macaque groups and making alarm calls. Rhesus social behaviour has been described as despotic, in that high-ranking individuals often show little tolerance, and frequently become aggressive towards non-kin. Top-ranking female rhesus monkeys are known to sexually coerce unreceptive males and also physically injure them, biting off digits and damaging their genitals.
Rhesus macaques have been observed engaging in interspecies grooming with and with Sambar deer.
Manson and Parry found that free-ranging rhesus macaques avoid inbreeding. Adult females were never observed to copulate with males of their own matrilineage during their fertile periods.
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 their 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 center 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.
Conflict between rhesus macaques and humans is at all-time high, with areas once forested habitat being converted to industrial agriculture. In Nepal, the expansion of monocultures, increased forest fragmentation, degradation of natural habitats and changing agricultural practices have led to a significant increase in the frequency of human-macaque conflict. Crop raiding is one of the biggest visible effects of human-rhesus conflict. The estimated financial cost to individual farmer households of macaque corn and rice raiding is approximately US$14.9 or 4.2% of their yearly income. This has resulted in farmers and other members of the population viewing macaques inhabiting agricultural landscapes as serious crop pests. Nepal is a significant study area with almost 44% of Nepal's land area containing suitable habitat for rhesus macaques but only having 8% of such suitable area being protected national parks. Rhesus macaques are rated as one of the top ten crop-raiding wildlife species in Nepal, which adds to their negative perception.
Suggestions to mitigate conflict include "prioritizing forest restoration programs, strategic management plans designed to connect isolated forest fragments with high rhesus macaque population densities, creating government programs that compensate farmers for income lost due to crop-raiding, and educational outreach that informs local villagers of the importance of conservation and protecting biodiversity". Mitigation strategies offers the most effective solutions to reduce conflict occurring between rhesus macaques and humans in Nepal.
India is another country that is seeing the rise of human-macaque conflict. Macaque-human conflict particularly occurs in the twin hill-states of Uttarakhand and Himachal Pradesh with such conflict being a source of contentious debate in political scenarios, resentment and polarization amongst agriculturalists and wildlife conservationists. In India, crop raiding by rhesus macaques has been identified as the main cause of conflict. In urban areas, rhesus macaques damage property and injure people in house raids to access food and provisions; in agricultural areas, they cause financial losses to farmers due to crop depredation. The estimated extent of crop damages in Himachal Pradesh ranges from 10–100% to 40–80% of all crop losses. The financial implications of such damage is estimated at approximately USD$200,000 in agriculture and USD$150,000 in horticulture. Quantification of crop and financial loses is challenging. Farmers' negative views of macaques may cause them to perceive higher than actual losses. This has led to harsh actions against rhesus macaque communities. Other factors in rhesus perception include economic status, farmer economic stability, cultural attitudes towards the given species and the frequency and intensity of wildlife conflicts. All of the above have resulted in changes in conservation and management with legal rhesus macaque culling issued in 2010.
Human-macaque conflict is also occurring in China, specifically in the area of Longyang District, Baoshan City, Yunnan Province. The peak period of conflict occurs from August–October. Factors associated with accessibility and availability of food and shelter appear to be the key drivers of human-macaque conflict, with an overall increase between the years of 2012 and 2021.
One key factor of conflict that directly affects the human-macaque relationship is visibility. Visibility of rhesus macaques in agroecosystem-dominated areas largely impacts conflict between humans and rhesus macaques. The conspicuous presence of rhesus macaques in and around farms results in farmers believing that macaques cause heavy crop depredations which, in turn, have led to negative perceptions and actions against the species. Whereas visibility in urban areas can result in a positive relationship, areas include around temples, and tourist areas where their dietary needs are largely met by food provisioning.
Towards the end of March 2018, it was reported that a monkey had entered a house in the village of Talabasta, Odisha, India and kidnapped a baby. The baby was later found dead in a well. Though monkeys are known to attack people, enter homes and damage property, this reported behaviour was unusual.
In areas of tourism, human behaviour change is necessary to prevent conflict. One method is to introduce public education programs as well as restrict visitors to specific viewing platforms, with the goal to minimize physical proximity. An important aspect is enforcing no feed regulations that only allow provisioning by trained staff at scheduled times. Regulating visitor behaviours that provoke aggressive responses from macaques, including noise regulation, greatly benefits conflict reduction. Replacing food-conditioned behaviours established by human visitors and further human education will greatly aid in returning co-existence between rhesus macaques and humans.
Another method of population management is translocation. Translocation of problem macaques in urban rhesus communities in India has been employed as a non-lethal solution to human–macaque conflicts. Translocation can be seen as a short-term fix, as macaques may return or other rhesus groups may take their place. Translocation is also hampered by a lack of suitable alternate locations.
Another tool of population management is sterilisation and/or contraceptive programmes. Fertility control looks to be a feasible management tool for reducing human–macaque conflict because it avoids the extermination of the animals and avoids costs and problems associated with translocation. Although there is potential for sterilization and general fertility control to be positive, there is limited research and understanding of the long-term effects of sterilization programs and its effectiveness.
The U.S. Army, the U.S. Air Force, and NASA launched rhesus macaques into outer space during the 1950s and 1960s, and the Soviet/Russian space program launched them into space as recently as 1997 on the Bion program. Albert II became the first primate and first mammal in space during a U.S. V-2 rocket suborbital flight on 14 June 1949, and died on impact when a parachute failed.
Another rhesus monkey, Able, was launched on a suborbital spaceflight in 1959, and was among the first living beings (along with Miss Baker, a squirrel monkey on the same mission) to travel in space and return alive.
On 25 October 1999, the rhesus macaque became the first cloning primate with the birth of Tetra. January 2001 had the birth of ANDi, the first transgenic primate; ANDi carries foreign 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 Center of the University of Puerto Rico on the island of Cayo Santiago, off Puerto Rico, where approximately 1800 of the monkeys live. No predators are 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 half of its food comes from natural foraging.
Rhesus macaques, like many macaques, carry the herpes B virus. This virus does not typically harm the monkey, but is very dangerous to humans in the rare event that it zoonosis, for example in the 1997 death of Yerkes National Primate Research Center researcher Elizabeth Griffin.
Comparison of rhesus macaques, chimpanzees, and humans revealed the structure of ancestral primate genomes, positive selection pressure and lineage-specific expansions, and contractions of gene families. "The goal is to reconstruct the history of every gene in the human genome," said Evan Eichler, University of Washington, Seattle. DNA from different branches of the primate tree will allow us "to trace back the evolutionary changes that occurred at various time points, leading from the common ancestors of the primate clade to Homo sapiens," said Bruce Lahn, University of Chicago.
After the human and chimpanzee genomes were sequenced and compared, it was usually impossible to tell whether differences were the result of the human or chimpanzee gene changing from the common ancestor. After the rhesus macaque genome was sequenced, three genes could be compared. If two genes were the same, they were presumed to be the original gene.
The chimpanzee and human genome diverged 6 million years ago. They have 98% identity and many conserved regulatory regions. Comparing the macaque and human genomes, further identified evolutionary pressure and gene function. Like the chimpanzee, changes were on the level of gene rearrangements rather than single mutations. Frequent insertions, deletions, changes in the order and number of genes, and segmental duplications near gaps, centromeres and telomeres occurred. So, macaque, chimpanzee, and human chromosomes are mosaics of each other.
Some normal gene sequences in healthy macaques and chimpanzees cause profound disease in humans. For example, the normal sequence of phenylalanine hydroxylase in macaques and chimpanzees is the mutated sequence responsible for phenylketonuria in humans. So, humans must have been under evolutionary pressure to adopt a different mechanism. Some gene families are conserved or under evolutionary pressure and expansion in all three primate species, while some are under expansion uniquely in human, chimpanzee, or macaque. For example, cholesterol pathways are conserved in all three species (and other primate species). In all three species, immune response genes are under positive selection, and genes of T cell-mediated immunity, signal transduction, cell adhesion, and membrane proteins generally. Genes for keratin, which produce hair shafts, were rapidly evolving in all three species, possibly because of climate change or mate selection. The X chromosome has three times more rearrangements than other chromosomes. The macaque gained 1,358 genes by duplication. Triangulation of human, chimpanzee, and macaque sequences showed expansion of gene families in each species.
The PKFP gene, important in sugar (fructose) metabolism, is expanded in macaques, possibly because of their high-fruit diet. So are genes for the olfactory receptor, cytochrome P450 (which degrades toxins), and CCL3L1-CCL4 (associated in humans with HIV susceptibility). Immune genes are expanded in macaques, relative to all four great ape species. The macaque genome has 33 major histocompatibility genes, three times those of human. This has clinical significance because the macaque is used as an experimental model of the human immune system.
In humans, the preferentially expressed antigen of melanoma (PRAME) gene family is expanded. It is actively expressed in cancers, but normally is testis-specific, possibly involved in spermatogenesis. The PRAME family has 26 members on human chromosome 1. In the macaque, it has eight, and has been very simple and stable for millions of years. The PRAME family arose in translocations in the common mouse-primate ancestor 85 million years ago, and is expanded on mouse chromosome 4.
DNA microarrays are used in macaque research. For example, Michael Katze of University of Washington, Seattle, infected macaques with 1918 and modern influenzas. The DNA microarray showed the macaque genomic response to human influenza on a cellular level in each tissue. Both viruses stimulated innate immune system inflammation, but the 1918 flu stimulated stronger and more persistent inflammation, causing extensive tissue damage, and it did not stimulate the interferon-1 pathway. The DNA response showed a transition from innate to adaptive immune response over seven days.
The full sequence and annotation of the macaque genome is available on the Ensembl genome browser.
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