Squirrel monkey

Last updated • 10 min readFrom Wikipedia, The Free Encyclopedia

Squirrel monkeys [1]
Temporal range: Miocene (Laventan to recent
13.8–0  Ma
Saimiri sciureus-1 Luc Viatour.jpg
Common squirrel monkey
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Cebidae
Subfamily: Saimiriinae
Miller, 1912 (1900)
Genus: Saimiri
Voigt, 1831
Type species
Simia sciurea
Species
Synonyms
  • LaventianaRosenberger, 1991 [2]
  • NeosaimiriStirton, 1951 [2]
Squirrel monkey in Yacuma Park, Bolivia Wild-57.jpg
Squirrel monkey in Yacuma Park, Bolivia

Squirrel monkeys are New World monkeys of the genus Saimiri. Saimiri is the only genus in the subfamily Saimiriinae. The name of the genus is of Tupi origin (sai-mirím or çai-mbirín, with sai meaning 'monkey' and mirím meaning 'small') [3] and was also used as an English name by early researchers. [4] [5]

Contents

Squirrel monkeys live in the tropical forests of Central and South America in the canopy layer. Most species have parapatric or allopatric ranges in the Amazon, while S. oerstedii is found disjunctly in Costa Rica and Panama.

There are two main groups of squirrel monkeys recognized. They are differentiated based on the shape of the white coloration above the eyes. In total there are five recognized species. [6] [7] Squirrel monkeys have short and close fur colored black at the shoulders, yellow or orange fur along the back and extremities, and white on the face. [8]

Squirrel monkeys have determined breeding seasons which involve large fluctuations in hormones and there is evidence of sexual dimorphism between males and females. [9]

Squirrel monkeys can only sweat through the palms of their hands and feet. This can have the effect of making their hands and feet feel damp to the touch. Squirrel monkeys must make use of other thermoregulation techniques such as behavioral changes and urine washing. [10] These monkeys live in habitats of high temperatures and high humidity, making it essential for them to maintain proper osmoregulation if conditions pass certain thresholds. [11] Color vision studies have also been performed on squirrel monkeys for the purpose of better understanding vision ailments in humans. [12]

The common squirrel monkey is commonly captured for the pet trade and for medical research, [13] but it is not threatened. Two squirrel monkey species are endangered: the Central American squirrel monkey and the black squirrel monkey are listed as vulnerable by the IUCN. [6] [14]

Evolutionary history

Miss Baker, an 'astronaut' squirrel monkey, rode into space as part of the United States space program, and returned safely. Miss Baker, the squirrel monkey.jpg
Miss Baker, an 'astronaut' squirrel monkey, rode into space as part of the United States space program, and returned safely.

Taxonomy

Until 1984, all South American squirrel monkeys were considered part of a single widespread species, and many zoologists considered the Central American squirrel monkey to be a member of that single species as well. [1] [7] The two main groups currently recognized can be separated by the white above the eyes; it is shaped as a Gothic ("pointed") arch in the S. sciureus group, while it is shaped as a Roman ("rounded") arch in the S. boliviensis group. [15] Mammal Species of the World (2005) recognized five species. [1]

Subsequent taxonomic research has recognized Saimiri sciureus cassiquiarensis as a separate species Saimiri cassiquiarensis , and also recognized an additional species, Collins' squirrel monkey Saimiri collinsi that had previously been considered to be within S. sciureus. [16] Some more recent taxonomies also recognize Saimiri sciureus macrodon as a separate species Saimiri macrodon, but others recognize S. macrodon to be a synonym of Saimiri cassiquiarensis. [17] [18] [19] [20]

Evolution

The crown group of the extant squirrel monkeys appears to have diverged around 1.5 million years ago. [21] Diversification of squirrel monkey species appears to have occurred during the Pleistocene Epoch, likely due to climatic changes associated with interglacial periods in South America at the time. The origin of squirrel monkeys in Central America is unclear, but a possible hypothesis is human transport. More genetic work needs to be done on the subject to reveal a true answer. [21] S. boliviensis appears to be the first diverging species in the group. S. oerstedii and S. s. sciureus, are sister species. S. s. macrodon is the sister species to the S. oerstedii / S. s. sciureus clade.[ clarification needed ]

Description

A squirrel monkey's fur is short and close, coloured black at the shoulders and yellowish orange on its back and extremities. The upper parts of their heads are hairy. This black-and-white face gives them the name "death's head monkey" in several Germanic languages (e.g., German Totenkopfaffen, Swedish dödskalleapor, Dutch doodshoofdaapjes) and Slovenian (smrtoglavka).

Squirrel monkeys grow from 25 to 35 centimetres (9.8 to 13.8 in) long, plus a 35 to 42 centimetres (14 to 17 in) tail. Male squirrel monkeys weigh 750 to 1,100 grams (26 to 39 oz). Females weigh 500 to 750 grams (18 to 26 oz). Both males and females are equipped with long and hairy tails, flat nails, and pointed claws. [8]

Female squirrel monkeys have pseudo-penises, which they use to display dominance over smaller monkeys, in much the same way that the male squirrel monkeys display their dominance.[ citation needed ]

Behaviour, ecology, and physiology

Like most of their New World monkey relatives, squirrel monkeys are diurnal and arboreal. Unlike other New World monkeys, their tail is not used for climbing but as a kind of "balancing pole" and also as a tool. Their movements in the branches can be very rapid.

Squirrel monkeys live together in multi-male/multi-female groups with up to 500 members. These large groups, however, can occasionally break into smaller troupes. The groups have a number of vocal calls, including warning sounds to protect the group from large falcons, which are a natural threat. Their small body size also makes them susceptible to predators such as snakes and felids. For marking territory, squirrel monkeys rub their tail and their skin with their own urine.

Squirrel monkeys are omnivores, eating primarily fruits and insects. Occasionally, they also eat seeds, leaves, flowers, buds, nuts, and eggs.

Sexual dimorphism in squirrel monkeys: larger adult male. Spotted in Piedras Blancas National Park, Golfo Dulce, Costa Rica Large Male Squirrel Monkey.jpg
Sexual dimorphism in squirrel monkeys: larger adult male. Spotted in Piedras Blancas National Park, Golfo Dulce, Costa Rica

Reproduction

Squirrel monkey mating is subject to seasonal influences. Squirrel monkeys reach sexual maturity at ages of 2–2.5 years for females and age 3.5–4 years for males. Females give birth to young during the rainy season, after a 150- to 170-day gestation. Only the mothers care for the young. Saimiri oerstedti are weaned by 4 months of age, while S. boliviensis are not fully weaned until 18 months old. Squirrel monkeys live to about 15 years old in the wild, and over 20 years in captivity. Menopause in females probably occurs in the mid-teens. [22] Studies show that Saimiri collinsi time the weaning of their young with the period of time when there will be maximum fruit availability in the environment. This reduces the energetic struggles that newly weaned juveniles will face when transitioning from a milk diet where they are dependent on their mother for food to a more diverse diet where they have to forage for food. [23] There is evidence that squirrel monkeys show sexual dimorphism during the breeding season. In the months leading up to breeding and in the months of breeding, sexually mature adult males have been recorded to increase in size by significant amounts relative to females. These size changes are caused by seasonal fluctuations in androgen hormones synthesized in the hypothalamus, pituitary, adrenal and gonadal axes. The fluctuations include increases in the concentrations of testosterone, androstenedione, and dehydroepiandrosterone levels in sexually mature males during the breeding season, peaking in January. Following the breeding season, these androgen concentrations drop. [9] The evolutionary reasoning for these size changes in sexually mature males is suggested to be both intra-sexual selections among males and also female choice selection, as the larger males are more likely to be preferred by females and partake in more copulations. There is not clear evidence yet as to why females choose larger males, but a leading hypothesis is that the larger males are more likely to have better vigilance for their young. [24]

Thermoregulation

Squirrel monkeys can only sweat through the palms of their hands and the soles of their feet. Sweating in these areas alone does not provide enough cooling for the monkeys to survive in the high temperature environments of South and Central America, requiring them to use other methods to thermoregulate. They will use behavioral tactics such as seeking out shaded areas sheltered from the sun and also make use of postural changes to better dissipate heat from their body. They will also make use of a technique to maximize evaporative cooling known as urine washing. The monkeys will urinate on their hands and rub the urine over the soles of their feet. The urine is then evaporated off the body in a cooling process. Studies have shown this behavior to be maximized during times of high temperature, highlighting its importance as a thermoregulatory behavior. [10]

Osmoregulation

Squirrel monkeys are subject to both high temperatures and high humidity in their natural habitat. The humidity can range from 70% saturation in the 'dry' season up to 90% in the 'wet' season. Squirrel monkeys are able to tolerate up to 75% humidity with small adjustments in behavior and physiology that increase in significance as the humidity goes up. When reaching approximately 95% humidity, the monkeys have more drastic changes in osmoregulation in order to maintain homeostasis. As evaporative water loss decreases at these high levels of saturation, the monkeys will take in less water and create a more concentrated urine in order to maintain proper ion and water levels inside the body. [11]

Cooperation Studies

Cooperation is largely evident in human primates. Squirrel monkeys do not often display cooperation in the wild, while many other nonhuman primates do. Studies have been done to suggest that female squirrel monkeys show disadvantageous inequity aversion as it pertains to food rewards. However, the same could not be said for male squirrel monkeys. More studies need to be done on squirrel monkey behavior to determine why squirrel monkeys rarely show cooperation, and whether disadvantageous inequity aversion is a relevant factor. [25]

Colour vision

Colour vision in squirrel monkeys has been extensively studied as a stand-in for human ailments. [12] In humans, two genes for colour vision are found on the X chromosome. Typically, one gene (OPN1LW) produces a pigment that is most sensitive to the 564 nm wavelength, while the other gene (OPN1MW) produces a pigment most sensitive to 534 nm. In squirrel monkeys, there is only one gene on the X chromosome but it exists in three varieties: one is most sensitive to 538 nm, one to 551 nm, and one to 561 nm. Since males have only one X chromosome, they are dichromatic, although with different sensitivities. Females have two X chromosomes, so some of them can have copies of two different alleles. The three alleles seem to be equally common, leading to one-third of females being dichromatic, while two-thirds are trichromatic. [26] Recently, gene therapy has given the human OPN1LW gene to adult male squirrel monkeys, producing behaviour consistent with trichromatic colour vision. [12]

Related Research Articles

<span class="mw-page-title-main">Cebidae</span> Family of New World monkeys

The Cebidae are one of the five families of New World monkeys now recognised. Extant members are the capuchin and squirrel monkeys. These species are found throughout tropical and subtropical South and Central America.

<span class="mw-page-title-main">Panamanian white-faced capuchin</span> Species of primate

The Panamanian white-faced capuchin, also known as the Panamanian white-headed capuchin or Central American white-faced capuchin, is a medium-sized New World monkey of the family Cebidae, subfamily Cebinae. Native to the forests of Central America, the white-faced capuchin is important to rainforest ecology for its role in dispersing seeds and pollen.

<span class="mw-page-title-main">Common marmoset</span> Species of New World monkey

The common marmoset, also called white-tufted marmoset or white-tufted-ear marmoset, is a New World monkey. It originally lived on the northeastern coast of Brazil, in the states of Piauí, Paraíba, Ceará, Rio Grande do Norte, Pernambuco, Alagoas, and Bahia. Through release of captive individuals, it has expanded its range since the 1920s to Southeast Brazil, where it became an invasive species, raising concerns about genetic pollution of similar species, such as the buffy-tufted marmoset, and predation upon bird nestlings and eggs.

<span class="mw-page-title-main">Common squirrel monkey</span> Common name for multiple mammal species

Common squirrel monkey is the traditional common name for several small squirrel monkey species native to the tropical areas of South America. The term common squirrel monkey had been used as the common name for Saimiri sciureus before genetic research by Jessica Lynch Alfaro and others indicated S. scuireus covered at least three and possibly four species: the Guianan squirrel monkey, Humboldt's squirrel monkey and Collins' squirrel monkey. The Ecuadorian squirrel monkey, generally regarded as a subspecies of Humboldt's squirrel monkey, had also been sometimes proposed as a separate species that had originally been included within the term "common squirrel monkey."

<span class="mw-page-title-main">Black squirrel monkey</span> Species of New World monkey

The black squirrel monkey, also known as the blackish squirrel monkey or black-headed squirrel monkey, is a small New World primate, endemic to the central Amazon in Brazil. It largely resembles the female of the far more common Bolivian squirrel monkey, though the latter lacks the black central back.

<span class="mw-page-title-main">Black-capped squirrel monkey</span> Species of New World monkey

The black-capped squirrel monkey is a species of New-World monkey native to the upper Amazon basin in Bolivia, western Brazil and eastern Peru. They weigh between 365 and 1,135 g and measure, from the head to the base of the tail, between 225 and 370 mm. Black-capped squirrel monkeys are primarily tree-dwelling and are found in both native and plantation forests as well as some farmed areas near running water. Their diet is omnivorous and mostly consists of flowers, fruit, leaves, nuts, seeds, insects, arachnids, eggs and small vertebrates. They mostly live in female-dominated troops of around 40 to 75 monkeys, with males having been observed to disperse to live in all-male troops after reaching sexual maturation. Their current conservation status according to the IUCN is 'Least Concern'. The species belongs to the genus Saimiri and has two subspecies, S. b. boliviensis and S. b. peruviensis.

<span class="mw-page-title-main">White-eared titi monkey</span> Species of New World monkey

The white-eared titi monkey also known as the Bolivian titi or Bolivian gray titi, is a species of titi monkey, a type of New World monkey, from eastern Bolivia and an area of western Brazil. The species has a range that extends east from the Manique River in Beni Department, Bolivia to southern Rondônia in Brazil. The southern end of its range includes forests around the city of Santa Cruz de la Sierra.

<span class="mw-page-title-main">Central American squirrel monkey</span> Species of New World monkey

The Central American squirrel monkey, also known as the red-backed squirrel monkey, is a squirrel monkey species from the Pacific coast of Costa Rica and Panama. It is restricted to the northwestern tip of Panama near the border with Costa Rica, and the central and southern Pacific coast of Costa Rica, primarily in Manuel Antonio and Corcovado National Parks.

Manfred Maurus was a German scientist, an assistant professor at the Ludwig Maximilian University of Munich, researcher, and head of the Department of Behavioral Physiology at the Max Planck Institute of Psychiatry. Maurus was a pioneer in neuroethology, commencing his work with Dr. Detlev Ploog. He specialized in investigating the neural basis of behavior in freely behaving squirrel monkeys, using radio-controlled electrical brain stimulation. Among his coworkers were Helmut Pruscha, Birgit Kühlmorgen, Paul Müller-Preuss, and Uwe Jürgens.

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<span class="mw-page-title-main">Sexual dimorphism in non-human primates</span> Sexual differences in primates

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<span class="mw-page-title-main">Black-crowned Central American squirrel monkey</span> Subspecies of New World monkey

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<span class="mw-page-title-main">Grey-crowned Central American squirrel monkey</span> Subspecies of New World monkey

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<span class="mw-page-title-main">Humboldt's squirrel monkey</span> Species of New World monkey

Humboldt's squirrel monkey is a species of squirrel monkey from Brazil, Colombia, Ecuador, Peru and Venezuela. It had previously been considered a subspecies of the common squirrel monkey, S. scuireus, but was elevated to full species status based on a genetic study by Carretero-Pinzón in 2009. A genetic study by Jessica Lynch Alfaro, et al indicated that the Ecuadorian squirrel monkey may be synonymous with Saimiri cassiquiarensis. As of 2018, the Ecuadorian squirrel monkey is generally regarded as a subspecies of Humboldt's squirrel monkey, S. cassiquiarensis macrodon.

<span class="mw-page-title-main">Guianan squirrel monkey</span> Species of New World monkey

The Guianan squirrel monkey is a species of squirrel monkey from Guiana, Venezuela and Brazil. S. sciureus formerly applied to Humboldt's squirrel monkey and Collins' squirrel monkey, but genetic research in 2009 and 2015 revealed that these are distinct species.

<span class="mw-page-title-main">Collins' squirrel monkey</span> Species of New World monkey

Collins' squirrel monkey is a species of squirrel monkey endemic to Brazil. It had been considered a subspecies of the common squirrel monkey until a genetic study by Jessica Lynch Alfaro et al. elevated it to species status.

<span class="mw-page-title-main">Ecuadorian squirrel monkey</span> Subspecies of New World monkey

The Ecuadorian squirrel monkey is a type of squirrel monkey. It had been considered a subspecies of the Guianan squirrel monkey, Saimiri sciureus, but was elevated to a full species, S. macrodon, based on a 2009 study by Carretero-Pinzón, et al. Based on subsequent genetic research by Jessica Lynch Alfaro, et al it was again reclassified as a subspecies of Humboldt's squirrel monkey.

References

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  2. 1 2 3 4 Saimiri – Paleobiology Database
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  12. 1 2 3 Mancuso, Katherine; Hauswirth, William W.; Li, Qiuhong; Connor, Thomas B.; Kuchenbecker, James A.; Mauck, Matthew C.; Neitz, Jay; Neitz, Maureen (2009-09-16). "Gene therapy for red–green colour blindness in adult primates". Nature. 461 (7265): 784–787. Bibcode:2009Natur.461..784M. doi:10.1038/nature08401. ISSN   0028-0836. PMC   2782927 . PMID   19759534.
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  14. ↑ Wong, G.; Cuarón, A.D.; Rodriguez-Luna, E. & de Grammont, P.C. (2008). "Saimiri oerstedii". IUCN Red List of Threatened Species . 2008: e.T19836A9022609. doi: 10.2305/IUCN.UK.2008.RLTS.T19836A9022609.en .
  15. ↑ Rowe, N. (1996). The Pictorial Guide to the Living Primates . Pogonia Press, Charlestown, Rhode Island. ISBN   978-0-9648825-0-8.
  16. ↑ Merces, Michelle P.; Lynch Alfaro, Jessica W.; et al. (January 2015). "Morphology and mitochondrial phylogenetics reveal that the Amazon River separates two eastern squirrel monkey species: Saimiri sciureus and S. collinsi". Molecular Phylogenetics and Evolution. 82 (B): 426–435. Bibcode:2015MolPE..82..426M. doi:10.1016/j.ympev.2014.09.020. PMID   25451802.
  17. ↑ Lynch Alfaro, J.W.; et al. (2015). "Biogeography of squirrel monkeys (genus Saimiri): South-central Amazon origin and rapid pan-Amazonian diversification of a lowland primate". Molecular Phylogenetics and Evolution. 82: 436–454. Bibcode:2015MolPE..82..436L. doi: 10.1016/j.ympev.2014.09.004 . PMID   25305518.
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  23. ↑ Stone, Anita I.; Ruivo, Luana V. P. (2020). "Synchronization of weaning time with peak fruit availability in squirrel monkeys (Saimiri collinsi) living in Amazonian Brazil". American Journal of Primatology. 82 (7): e23139. doi:10.1002/ajp.23139. ISSN   1098-2345. PMID   32333419.
  24. ↑ Boinski, S. (1987). "Mating Patterns in Squirrel Monkeys (Saimiri oerstedi): Implications for Seasonal Sexual Dimorphism". Behavioral Ecology and Sociobiology. 21 (1): 13–21. Bibcode:1987BEcoS..21...13B. doi:10.1007/BF00324430. ISSN   0340-5443. JSTOR   4600051. S2CID   23241941.
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