Macaca fascicularis, variously known by common names such as crab-eating macaque, long-tailed macaque, or cynomolgus monkey, is a macaque species native to Southeast Asia. As a synanthropic species, the crab-eating macaque thrives near human settlements and in secondary forests. The crab-eating macaque has developed a variety of cultural perceptions, from being smart and adaptive, to being sacred, to even being pests in some cases.
The crab-eating macaque is omnivorous and frugivorous. It lives in matrilineal groups ranging from 10 to 85 individuals, with groups exhibiting female philopatry and males emigrating from natal group at puberty. The crab-eating macaque is the only old-world monkey known to use stone tools in their daily foraging, and it engages in a robbing and bartering behavior in some tourist locations.
The crab-eating macaque is the most traded primate species and also the most popular species used in scientific research. Due to these threats, the crab-eating macaque was listed as Endangered on the IUCN Red List in 2022.
Etymology Macaca comes from the Portuguese word , which was derived from makaku, a word in Ibinda, a language of Central Africa (kaku means monkey in Ibinda). The specific epithet fascicularis is Latin for a small band or stripe. Sir Thomas Raffles, who gave the animal its scientific name in 1821, did not specify what he meant by the use of this word.
In Indonesia and Malaysia, the crab-eating macaque and other macaque species are known generically as kera.
The crab-eating macaque has several common names. It is often referred to as the long-tailed macaque due to its tail, which is the length of their body and head combined. The name crab-eating macaque refers to it being seen foraging beaches for crabs. Another common name for M. fascicularis, often used in laboratory settings, is the cynomolgus monkey which derives from Greek Kynamolgoi meaning "dog milkers". It has also been suggested that cynomolgus refers to a race of humans with long hair and handsome beards who used dogs for hunting according to Aristophanes of Byzantium, who seemingly derived the etymology of the word cynomolgus from the Greek κύων, cyon 'dog' (gen. cyno-s) and the verb , 'to milk' (adj. amolg-os), by claiming that they milked female dogs.Aristophanes of Byzantium, Tῶν Ἀριστοτέλους περί ζώων ἐπιτομή. ΑΠΑΝΤΑ Ι, 2.59. ΚΑΚΤΟΣ 1998.
Perceptions and terminology The crab-eating macaque is understood and perceived in many ways: smart, pestiferous, exploited, sacred, vermin, invasive.
In 2000 the crab-eating macaque was placed on the list of 100 most invasive species. For example, it is considered an invasive alien species (IAS) on Mauritius, articles argue for long-tailed macaques spreading seeds of invasive plants, competing with native species like the Mauritian flying fox, and having a detrimental impact on native threatened species. Several authors pointed out that the present evidence indicates that predation on birds by monkeys may have been overestimated. Some address these accusations and they point out the crab-eating macaques do not prefer primary forest thus it is unlikely that Mauritius macaques were ever a major source of indigenous forest destruction. The primary driver of bird extinction has been habitat destruction by humans. Sussman and Tattersall mention that the Dutch abandoned the island in 1710–1712 due to monkeys and rats destroying plantations, they point out that the human population was low at this time and the crab-eating macaques would have had plenty of primary forest to exploit, yet they chose to brave the dangers of raiding plantations. They do not deny that macaques on Mauritius prey on bird eggs and disseminate seeds of exotic plants yet the major loss of species on Mauritius is due to habitat loss caused by humans – macaques are successful because they prefer secondary forest and disturbed habitats. This is significant because the perception of crab-eating macaques being invasive and destructive to "native" biodiversity are used as a justification for use in biomedical research.
"Weed" and "non-weed" species are distinguished based on that species ability to thrive in close proximity and association with human settlements. This label was not intentionally proposed to disparage crab-eating macaques but this term, like pest and invasive, can affect how people perceive this species and can trigger negative perceptions.
Taxonomy Ten subspecies of the crab-eating macaque were proposed: M. f. fascicularis – Indonesia, Malaysia, Philippines, Thailand, Cambodia, Singapore, Vietnam M. f. aurea – Myanmar, Laos, western and southern Thailand near Myanmar border M. f. antriceps – Kram Yai Island, Thailand M. f. condorensis – Con Son Island, Hon Ba Island, Vietnam M. f. karimondjiwae – Karimunjawa Islands, Indonesia M. f. umbrosa – Nicobar Islands, India M. f. fusca – Simeulue Island, Indonesia M. f. lasiae – Lasia Island, Indonesia M. f. tua – Maratua Island, Indonesia M. f. philippinensis is under dispute and included with M.f. fascicularis.
M. f. fascicularis has the largest range, followed by M. f. aurea. The other seven subspecies are isolated on small shallow-water fringe-islands and deep-water fringing-islands.
Evolution The macaque originated in northeastern Africa some 7 million years ago and spread through most of continental Asia by , and subdivided into four groups (sylvanus, sinica, silenus, and fascicularis). The earliest split in the genus Macaca likely occurred ~4.5 mya between an ancestor of the silenus group and a fascicularis-like ancestor from which non-silenus species later evolved. The species of the fascicularis group (which include m. fascicularis, m. mulatta, and m. fuscata) share a common ancestor that lived 2.5 mya. It is suggested that M. fascicularis are the most plesiomorphic (ancestral) taxon in the fascicularis clade, thus it is argued that M. mulatta evolved from a fascicularis-like ancestor that reached mainland from its homeland in Indonesia around 1 mya.
A phylogenetic analysis found evidence that the fascicularis group originated from an ancient hybridization between the sinica and silenus groups ~3.45–3.56 mya, soon after the initial separation of two parent lineages (proto-sinica and proto-silenus) ~3.86 mya. This divergence and subsequent hybridization occurred during rapid glacial-eustatic fluctuations in the early Pleistocene: high sea levels may have led to the initial separation of proto-sinica and proto-silenus while the subsequent lowering of sea levels facilitated the secondary contact needed for hybridization.
Known fossils indicate that crab-eating macaques inhabited the Sunda Shelf since at least early Pleistocene, ~1mya. It is likely that crab-eating macaques were introduced to Timor and Flores (both on the east side of the Wallace line), by humans around 4,000–5,000 years ago. Crab-eating macaques are the only species on both sides of the Wallace line.
The possible stages of crab-eating macaque evolution and dispersal were proposed:
Stage 1: more than , crab-eating dispersed into the Sunda Shelf area. Earliest fossil record of crab-eating macaques was found in Java (this collection included H. erectus and leaf monkey species). They probably reached Java by dry land during a period of glacial advance and low sea levels Stage 2: around 160 thousand years ago, dispersal and isolation of progenitors of the strongly differentiated deep water fringing island populations occurred. These include M.f. umbrosa, M.f. fusca, M.f., tua [fooden includes M.f. philippinensis but their subspecies status is currently under debate]. It is thought that the progenitors of these subspecies reached deep water habitats during the penultimate glacial maximum when sea levels were lower than present. These populations became isolated during the interglacial period around 120 kya Stage 3: more than 18 thousand years ago, the differentiation of progenitors of populations of the Indochinese peninsula and northern part of the isthmus of Kra occurred. These subspecies include M.f. aurea and M.f. fascicularis. These two subspecies became differentiated before the last glacial maximum Stage 4: 18 thousand years ago, the dispersal and isolation of progenitors of weakly differentiated deep water fringing island populations occurred (M. f. fascicularis) Stage 5: less than 18 thousand years ago, the isolation of the progenitors of shallow water fringing island populations and populations in Penida and Lombok (deep water) occurred. These subspecies include M.f. karimondjawae, M.f. atriceps, M.f. condorensis, M.f. fascicularis Stage 6: 4.5 thousand years ago, the dispersal and isolation of progenitors of populations in eastern lesser Sunda islands (deep water), occurred (M.f. fascicularis).
Characteristics The crab-eating macaque is sexually dimorphic, with males weighing between and females weighing . The height of an adult male is between and for adult females. Its tail is the length of its head and body combined. Dorsal pelage is generally greyish or brownish with a white underbelly with black and white highlights around the crown and face. The face skin is brownish to pinkish except for the eyelids which are white. Adults are usually bearded on and around the face, except for around the snout and eyes. Older females have the fullest beards, with males' being more whisker like. Subspecies on islands seem to have black coloration of their pelage, and large island and mainland subspecies are lighter.
Genetics
Along the northern part of its range, the crab-eating macaque hybridizes with the rhesus macaque (M. mulatta). It also has been known to hybridize with the southern pig-tailed macaque (M. nemestrina). Hybrids also occur across subspecies too. Rhesus and crab-eating macaques hybridize within a contact zone where their ranges overlap, which has been proposed to lie between 15 and 20 degrees north and includes Thailand, Myanmar, Laos, Vietnam. Their offspring are fertile, and they continue to mate which leads to a broad range of admixture proportions. Introgression from rhesus to crab-eating macaque populations extends beyond Indochina and the Kra Isthmus, whereas introgression from crab-eating to rhesus macaques is more restricted. There seems to be a rhesus biased and male biased gene flow between rhesus and crab-eating macaque populations which has led to different degrees of genetic admixture in these two species.
Distribution and habitat The crab-eating macaque's native range encompasses most of mainland Southeast Asia, through the Malay Peninsula and Singapore, the Maritime Southeast Asia islands of Sumatra, Java, and Borneo, offshore islands, the islands of the Philippines, and the Nicobar Islands in the Bay of Bengal. This primate is a rare example of a terrestrial mammal that violates the Wallace line, being found out across the Lesser Sunda Islands. It lives in a wide variety of habitats, including primary lowland rainforests, disturbed and secondary rainforests, shrubland, and riverine and coastal forests of nipa palm and mangrove. It also easily adjusts to human settlements and is considered sacred at some Hindu temples and on some small islands, but as a pest around farms and villages. Typically, it prefers disturbed habitats and forest periphery.
Introduction to other regions Humans have transported crab-eating macaques to at least five islands: Mauritius, Western New Guinea, Ngeaur, Tinjil Island near Java, and Kabaena Island off of Sulawesi, and to Kowloon Hills of Hong Kong.