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Dusky Leaf Monkey
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Cercopithecidae
Genus: Trachypithecus
Species:
T. obscurus
Binomial name
Trachypithecus obscurus
(Reid, 1837)

Dusky leaf monkey

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The dusky leaf monkey, spectacled langur, or spectacled leaf monkey (Trachypithecus obscurus) is a species of primate in the family Cercopithecidae. It is found in Peninsular Malaysia, Myanmar and Thailand,[1] and can occasionally be found in Singapore.[2] During the day, these small, folivorous primates divide in sub-groups and scavenge for vegetation and fruit throughout the tropical forests[3][4]. According to the IUCN, the dusky leaf monkey's population is declining due to habitat loss, poaching, and anthropogenic land use, which prompted the IUCN to classify the species as endangered in 2015.[1]

While the dusky leaf monkey's fur can evolve into shades of grey, brown, or black, they are born with an orange coating.

Article Draft

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Taxonomy

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Within the Cercopithecidae family, the dusky leaf monkey is a member of the lutung genus. Although most researchers agree with this classification, others believe that this primate should be categorized under the genus Presbytis.[5][6] Researchers have also disputed the number of subspecies that exist, with some claiming that there are 11,[7] while others claim there are seven. Currently, the following seven subspecies are officially recognized:[3][8][9]

  • Trachypithecus obscurus obscurus
  • Trachypithecus obscurus flavicauda
  • Trachypithecus obscurus halonifer
  • Trachypithecus obscurus carbo
  • Trachypithecus obscurus styx
  • Trachypithecus obscurus seimundi
  • Trachypithecus obscurus sanctorum[9][8][3]

Description

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The dusky leaf monkey can appear in different colour variations, depending on the sub-species. While dusky leaf monkeys are born with an orange coating, the colour of their fur evolves as they mature into adulthood.[2] Along the abdominal area, their fur is often several shades lighter than that of their dorsal area, which can develop in shades of brown, black, or grey. Surrounding their eyes are circular patterns of bright white fur.[7][10][11][12]

The dusky leaf monkey is a rather small primate. In a study conducted by G. J Burton, the average weight of the 25 male dusky leaf monkeys that were sampled was 7.39 kilograms, while that of the 44 female dusky leaf monkeys that were sampled was 6.47 kilograms. These results suggest that dusky leaf monkeys are sexually dimorphic species, as the females were found to be, on average, 12% smaller than the males sampled. Burton's study also revealed that, among the 25 male primates, there was a direct correlation with the weight of one testicle with the weight of the other, suggesting that one testicle may be used to estimate the weight of the other. However, the female ovaries were found to not be statistically significant enough to predict the weight of one ovary with the other.[13]

Distribution

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The dusky leaf monkey can be found across Malaysia, Myanmar, and Thailand, where they inhabit tropical forests.[1] However, these primates have occasionally been spotted in Singapore. Research conducted within the country between 2019 and 2020 revealed that three dusky leaf monkey individuals were located in August of 2019 within the northern region of the island, near the body of water that borders Singapore and Malaysia. While dusky leaf monkeys are not native to the region, researchers speculate that they are able to swim to the country. Researchers are concerned about these migratory patterns because these foreign primates can increase competition for resources, such as vegetation, and transfer diseases and pathogens to other native species that are not equipped to recover from them.[2]

Behaviour and Diet

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Dusky leaf monkeys feed in the emergent and canopy layers.

Numerous activity budgets have been conducted Across Malaysia to study the behavioural patterns of the dusky leaf monkey. For instance, one activity budget conducted in 2016 with 12,480 primates in Teluk Bahang, Malaysia found that, within the eight month period, dusky leaf monkeys spent 40% of their time positioning, 33% of their time feeding, and 20% of their day moving. The sampled primates also allocated their time allo-grooming (4%), playing (2%), and foraging (1%).[14] Ten years prior, another activity budget with 18 dusky leaf monkeys was conducted at the Penang Botanical Garden, which is also located in Malaysia. Researchers at the University of Kebangsaan concluded that, within 18 days, the dusky leaf monkeys that were sampled spent 40% of their day eating, almost 24% of their day resting, and approximately 22.5% of their time moving. The dusky leaf monkeys also allocated time for autogrooming (6.52%) and allo-grooming (1.33%), among other behaviours.[10] However, a more recent study conducted in Malaysia from November 2017 to February 2018 in Bukit Soga Perdana, a forested area that is heavily influenced by industrial activity, concluded that the dusky leaf monkeys sampled spent the majority of their days moving, although these results were skewed due to unfavorable weather conditions that occured during observations.[7]

Dusky leaf monkeys live in troops that separate into sub-groups while scavenging for food. They tend to consume leaves growing at higher elevations in the forest canopy. They often rest at these high elevations to feed on their foraged vegetation.[15][7] Fruit availability is season-dependent, and although research suggests that the dusky leaf monkey consumes more vegetation that fruit, it prefers to eat fruit when it is available.[4]

Research suggests that hostile behaviour within troops does not occur often. A study conducted in 1996 by researchers at the University of St. Andrews revealed that, after a group of dusky leaf monkeys engage in aggressive behaviour, conflict resolution occurs more frequently and much faster afterwards than within other primate species. In fact, reconciliation among dusky leaf monkeys can occur as quickly as 60 seconds after fighting, and can be instigated by either the aggressor or the receiver through gestures such as embracing.[16]

Mating

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In another study conducted by Burton, 44 male dusky leaf-monkeys were sampled and the seminiferous tubules within each gonadal were observed. Burton concluded that the seminiferous tubules within each gonadal remained the same size throughout the year, and that there was no evidence of seasonal variation in testicular weight. This reveals that the male dusky leaf monkey does not have a seasonal mating period and are able to reproduce throughout the year. Burton suggests that this may be the case due to the continuous, warm climates experienced within Southeast Asia, as the mating period for many seasonal breeders occurs during warming climates.[17]

The IUCN declared the dusky leaf monkey as an endangered species.

Status and Conservation

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As of 2015, the dusky leaf monkey is listed as an endangered species in the IUCN Red List. Notably, anthropogenic land-use within Southeast Asian forests have resulted in the endangerment of the dusky leaf monkey's natural habitat, resulting in noticeable population declines.[18][7] However, the dusky leaf monkey also faces other threats brought on through anthropogenic activities and the introduction of predators within their habitat. Notably, domesticated dog packs have been reported to hunt and kill the dusky leaf monkey. [19] The construction of roads within tropical forests has led to a large increase in road mortality among dusky leaf monkeys, and is seen to be one of the more prominent threats to the dusky leafy monkey's survival, along with habitat loss, habitat degradation, and poaching.[20][18] While the dusky leaf monkey is often killed for their meat,[1] there are other incentives to poach them as well, as they are considered agricultural pests across Southeast Asia. [3] In the 1960s, this prompted Malaysian business owners to shoot them as they were feeding on leaves within rubber plantations.[17] Infant dusky leaf monkeys are also hunted and sold as pets internationally. However, when owners attempt to domesticate these primates, they are often not properly cared for and die as a result.[2]

Collective action is being taken to help conserve the dusky leaf monkey. In 1977, the dusky leaf-monkey had been introduced and listed under appendix II in the CITES legislation.[21] Species under appendix II are considered to be near threatened or endangered. The trade of appendix II species is heavily regulated, and often illegal.[22]

References

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  1. ^ a b c d IUCN (2015-11-23). "Trachypithecus obscurus: Boonratana, R., Ang, A., Traeholt, C. & Thant, N.M.L.: The IUCN Red List of Threatened Species 2020: e.T22039A17960562". doi:10.2305/iucn.uk.2020-2.rlts.t22039a17960562.en. {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ a b c d Ang, A., Jabbar, S., & Khoo, M (2020). "Dusky Langurs Trachypithecus obscurus (Reid, 1837) (Primates: Cercopithecidae) in Singapore: potential origin and conflicts with native primate species". Journal of Threatened Taxa. 12: 15967–15974 – via Platinum Open Access.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ a b c d Rahman Aifat, Nor. (2020). "Taxonomic Revision and Evolutionary Phylogeography of Dusky Langur(Trachypithecus obscurus) in Peninsular Malaysia". Zoological Studies. 59: 2–11 – via ResearchGate.
  4. ^ a b Ruslin, Farhani; Matsuda, Ikki; Md-Zain, Badrul Munir (2019-01-01). "The feeding ecology and dietary overlap in two sympatric primate species, the long-tailed macaque (Macaca fascicularis) and dusky langur (Trachypithecus obscurus obscurus), in Malaysia". Primates. 60 (1): 41–50. doi:10.1007/s10329-018-00705-w. ISSN 1610-7365.
  5. ^ Napier, John Russell & Napier, P. H. (1967). A handbook of living primates: morphology, ecology and behaviour of nonhuman primates,. P. H. Napier. London,: Academic P. ISBN 0-12-513850-4. OCLC 255860.{{cite book}}: CS1 maint: extra punctuation (link)
  6. ^ Thongnetr, Weera; Sangpakdee, Wiwat; Tanomtong, Alongklod; Nie, Wenhui; Raso, Sayam; Pinthong, Krit (2021-11-27). "The chromosomal homology between dusky langur (Trachypithecus obscurus Ried, 1837) and human (Homo sapiens) revealed by chromosome painting". The Nucleus. doi:10.1007/s13237-021-00381-0. ISSN 0976-7975.
  7. ^ a b c d e Siti-Kauthar, M.; Najmuddin, M. F.; Md-Zain, B. M.; Abdul-Latiff, M. A. B. (2019). PrimaTourism: preliminary study on activity budget of dusky leaf monkey Trachypithecus obscurus obscurus in Bukit Soga Perdana, Batu Pahat, Johor. IOP Conference: Series Earth and Environmental Science. Vol. 269. doi:10.1088/1755-1315/269/1/012045.
  8. ^ a b Don E. Wilson, & DeeAnn M., Reeder (2005). Mammal species of the world : a taxonomic and geographic reference (3rd ed.). Baltimore: Johns Hopkins University Press. ISBN 0-8018-8221-4.
  9. ^ a b "Trachypithecus obscurus". Integrated Taxonomic Information System. Retrieved 2 November 2021.
  10. ^ a b Md-Zain, B.M. (2011). "The Activity Patterns of a Group of Cantor's Dusky Leaf Monkeys" (PDF). International Journal of Zoological Research. 7: 59–67.
  11. ^ Groves, Colin (2001). Primate Taxonomy. Washington, DC: Smithsonian Books. ISBN 978-1560988724.
  12. ^ Roos, C., R. Boonratana, J. Supriatna, J.R. Fellowes, C.P. Groves, S.D. Nash, A.B. Rylands and Mittermeier, R.A. (2014). "4. An updated taxonomy and conservation status review of Asian primates" (PDF). Asian Primates Journal. 4.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ Burton, G.J. (1981). "The Relationship Between Body and Gonadal Weights of the Dusky Leaf Monkey (Presbytis obscura)". International Journal of Primatology. 2 (4): 351–368.
  14. ^ Yap, J.; Ruppert, N.; Fadzly, N. (2016). Activity patterns and diet of a group of wild dusky leaf monkeys (Trachypithecus obscurus) in Penang, Malaysia. Seminar Ekologi Malaysia.
  15. ^ The ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. G. Gene Montgomery. Washington, D.C.: Smithsonian Institution Press. 1978. ISBN 0-87474-646-9. OCLC 4004986.{{cite book}}: CS1 maint: others (link)
  16. ^ Arnold, K, & Barton, R (2000). "Postconflict Behavior of Spectacled Leaf Monkeys (Trachypithecus obscurus). I. Reconciliation". International Journal of Primatology,. 22: 243–266 – via ResearchGate.{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  17. ^ a b Burton, G. J. (1984). "Testicular histology of the dusky leaf monkey (presbytis obscura) as it relates to birth pattern in Peninsular Malaysia". International Journal of Primatology. 5 (2): 183–195. doi:10.1007/BF02735740. ISSN 0164-0291.
  18. ^ a b Boonratana, Ramesh. "Of road kills and dead langurs. Malaysian Naturalist". CAB Reviews Perspectives in Agriculture Veterinary Science Nutrition and Natural Resources.
  19. ^ MOHD FAUDZIR, N., Haris, H., Atiqah Norazlimi, N., & Munir Md Zain, B. "PREDATION OF DOMESTIC DOGS (Canis lupus familiaris) ON SCHLEGEL'S BANDED LANGUR (Presbytis neglectus) AND CRESTED HAWK-EAGLE(Nisaetus cirrhatus) ON DUSKY LEAF MONKEY (Trachypithecus obscurus)IN MALAYSIA" (PDF). Journal of Sustainability Science and Management. Volume 14 Number 6: 43. {{cite journal}}: |volume= has extra text (help)CS1 maint: multiple names: authors list (link)
  20. ^ Lappan, Susan. "Primate Research And Conservation In Malaysia" (PDF). CAB Reviews Perspectives in Agriculture Veterinary Science Nutrition and Natural Resources: 5.
  21. ^ "Species+". speciesplus.net. Retrieved 2022-04-11.
  22. ^ "Convention on International Trade in Endangered Species of Wild Fauna and Flora | CITES". cites.org. Retrieved 2022-04-11.
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