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Bengal slow loris

TheBengal slow loris(Nycticebus bengalensis) ornorthern slow lorisis astrepsirrhineprimateand aspeciesofslow lorisnative to theIndian subcontinentandIndochina.Its geographic range is larger than that of any other slow loris species. Considered asubspeciesof theSunda slow loris(N. coucang) until 2001,phylogeneticanalysis suggests that the Bengal slow loris is most closely related to the Sunda slow loris. However, some individuals in both species havemitochondrial DNAsequences that resemble those of the other species, due tointrogressive hybridization.It is the largest species of slow loris, measuring 26 to 38 cm (10 to 15 in) from head to tail and weighing between 1 and 2.1 kg (2.2 and 4.6 lb). Like other slow lorises, it has a wet nose (rhinarium), a round head, flat face, large eyes, small ears, avestigialtail, and dense, woolly fur. The toxin it secretes from its brachial gland (ascent glandin its arm) differs chemically from that of other slow loris species and may be used to communicate information about sex, age, health, and social status.

Bengal slow loris[1]
CITESAppendix I(CITES)[3]
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Strepsirrhini
Family: Lorisidae
Genus: Nycticebus
Species:
N. bengalensis
Binomial name
Nycticebus bengalensis
(Lacépède,1800)
Range of the Bengal slow loris
Synonyms[4][5]
  • Lori bengalensisLacépède, 1800
  • Nycticebus cinereusMilne-Edwards,1867
  • Nycticebus tardigradus typicusLydekker,1905
  • Nycticebus tenasserimensisElliot,1913
  • Nycticebus incanusThomas,1921

The Bengal slow loris isnocturnalandarboreal,occurring in bothevergreenanddeciduous forests.It prefers rainforests with densecanopies,and its presence in its native habitat indicates a healthy ecosystem. It is aseed disperserand pollinator, as well as a prey item for carnivores. Its diet primarily consists of fruit, but also includes insects, tree gum, snails, and smallvertebrates.In winter, it relies on plant exudates, such as sap and treegum.The species lives in small family groups,marks its territorywith urine, and sleeps during the day by curling up in dense vegetation or in tree holes. It is aseasonal breeder,reproducing once every 12–18 months and usually giving birth to a single offspring. For the first three months, mothers carry their offspring, which reachsexual maturityat around 20 months. The Bengal slow loris can live up to 20 years.

The species is listed as endangered on theIUCN Red List,and is threatened with extinction due to growing demand in theexotic pettrade andtraditional medicine.It is one of the most common animals sold in local animal markets. In traditional medicine, it is primarily used by wealthy to middle-class, urban women following childbirth, but also to treat stomach problems, broken bones, and sexually transmitted diseases. It is also hunted for food and suffers fromhabitat loss.Wild populations have declined severely, and it islocally extinctin several regions. It is found within manyprotected areasthroughout its range, but this does not protect them from rampantpoachingandillegal logging.Critical conservation issues for this species include enhancing protection measures, stricter enforcement of wildlife protection laws, and increased connectivity between fragmented protected areas.

Taxonomy and phylogeny

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The Bengal slow loris was long considered a subspecies until it was recognized as a distinct species in 2001.

Nycticebus bengalensis,commonlyknown as the Bengal slow loris or northern slow loris,[6]is a strepsirrhine primate in theslow lorisgenus,Nycticebus.Formerly considered asubspeciesof theSunda slow loris(N. coucang), it was recognized as a distinct species in 2001 by taxonomist and primatologistColin Groves.[1]It is difficult to distinguish from the other species in its genus.[6]

To help clarify species and subspecies boundaries, and to establish whethermorphology-based classifications were consistent with evolutionary relationships, thephylogeneticrelationships within the genusNycticebushave been investigated usingDNA sequencesderived from themitochondrialmarkersD loopandcytochromeb.Although most of the recognized lineages ofNycticebus(includingN. pygmaeus,N. menagensis,andN. javanicus) were shown to be genetically distinct—the analysis suggested that DNA sequences from some individuals ofN. coucangandN. bengalensisapparently share a closer evolutionary relationship with each other than with members of their own species. The authors suggest that this result may be explained byintrogressive hybridization,as the tested individuals of these two taxa originated from a region ofsympatryin southern Thailand. The precise origin of one of theN. coucangindividuals was not known.[7]This hypothesis was corroborated by a 2007 study that compared the variations in mitochondrial DNA sequences betweenN. bengalensisandN. coucang,and suggested that there has beengene flowbetween the two species.[8]

Anatomy and physiology

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The Bengal slow loris has large eyes, a round head, and short ears, as shown in this illustration from the mid-19th century.

The Bengal slow loris is the largest species of slow loris, weighing 1 to 2.1 kg (2.2 to 4.6 lb),[9]and measuring between 26 and 38 cm (10 and 15 in) from head to tail. It has a skull length of more than 62 mm (2.4 in).[5]It has dense, woolly, brown-gray fur on its back and white fur on its underside.[6]It also has a clear dark stripe that runs up to the top of its head, but does not extend laterally towards the ears. Its forearm and hand are almost white. The limbs of thepelvisvary in color from brown to nearly white, and the feet are always pale.Moultingmay cause seasonal variations in the color of the dorsal surface.[10]Like other slow lorises, its tail isvestigialand it has a round head and short ears.[6][11]It has arhinarium(the moist, naked surface around the nostrils of the nose) and a broad, flat face with large eyes.[12]Its eyes reflect a bright orangeeye shine.[13]On its front feet, the second digit is smaller than the rest; the big toe on its hind footopposesthe other toes, which enhances its gripping power. Its second toe on the hindfoot has a curved "toilet-claw"that the animal uses for scratching and grooming, while the other nails are straight.[12]

In addition to being smaller than the Bengal slow loris, the sympatricSunda slow lorisalso differs in its coloring: it does not have the pale areas of the head,nape,and shoulders, and its overall color is atawny- or golden-brown.[10]Thepygmy slow loris(N. pygmaeus) is much smaller, with a skull length less than 55 mm (2.2 in).[5]It also lacks the dark dorsal stripe of the Bengal slow loris,[14]has dark brown fur, and longer ears.[15]

The Bengal slow loris has a small swelling on the ventral side of its elbow called the brachial gland, which secretes a pungent, clear oily toxin that the animal uses defensively by wiping it on itstoothcomb.[16]The oil has been analyzed usinggas chromatography coupled to mass spectrometry,and it has been shown that almost half of the several dozenvolatileor semi-volatile chemicals present do not occur in the closely related pygmy slow loris. The most predominant component was thephenoliccompoundm-cresol.[17]The authors of the study suggest that the chemically complex oils may help the lorises communicate with each other, allowing them to transmit by scent information about sex, age, health and nutritional status, anddominance.[18]

Behavior and ecology

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The Bengal slow loris will gouge the bark of thebastard myrobalatree to obtain exudates, an important food source—especially in winter seasons.

The preferred habitats of the Bengal slow loris range acrosstropicalandsubtropicalregions, and includeevergreenand semi-evergreen rainforests with forest edges and continuous, densecanopies.[6]It can also be found in bamboo groves.[19]It prefers habitats with larger diameter, tall trees with a large crown depth (defined as the length along the main axis from the tree tip to the base of thecrown); these areas are typically associated with greater food abundance, and decreased risk of predation.[20]Because of its preference for dense forests, it acts as a good indicator of the ecosystem's health.[6]

The species acts as an importantseed disperserand pollinator, as well as a prey item for several carnivores. The Bengal slow loris feeds on plant exudates such assap,gums,resins,andlatexes,particularly those from the familyFabaceae.Even though the species does not have keeled nails, it will scrape the plant, actively breaking its surface; this behavior resembles that ofmarmosetsand thefork-marked lemurs.[21]Exudates are also obtained by gouging holes in the bark. The winter food supply consists almost entirely of plant exudates. Thebastard myrobala(Terminalia belerica), a deciduous tree common in Southeast Asia, is a preferred source for exudates,[22]but it has also been observed taking plant exudates from a number offamilies:Moraceae(Artocarpus),Magnoliaceae(Manglietia), Fabaceae (Acacia,Bauhinia),Lecythidaceae(Careya arborea), andSterculiaceae(Pterospermum).[9]Although it will feed on large insects (such askatydidsand crickets),[23]gum, snails, small birds, and reptiles, it is primarilyfrugivorous.[6]Lianasof the flowering plant genusBauhiniaare a commonly-used food source.[20]

A nocturnal animal, the Bengal slow loris has excellentnight vision,enhanced by atapetum lucidum—a layer of tissue in the eye that reflects visible light back through the retina. It sleeps during the day curled up in a ball in dense vegetation or in tree holes. Males and females mark theirterritorywith urine.[23]The species is known to live in small family groups.[6]Animals may practicesocial grooming.[23]

Reproduction

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The Bengal slow loris is not aseasonal breeder,unlike the pygmy slow loris.[8]Females in anestrous cycleattract males with a loud whistle. Females reproduce every 12–18 months and have a six-monthgestation.[23]Because they are not seasonal breeders, females could become pregnant when their offspring are approximately 6 months old, making possible for females to produce two offspring per year.[8]Females typically give birth to a single offspring, although twins rarely occur.[23]This differs from the sympatric pygmy slow loris, which commonly has twins.[8]The mother carries her young about three months before they become independent, although they may be temporarily left on branches while the mother searches for food.[23]Sexual maturityis reached at approximately 20 months of age.[6]The species is known to live up to 20 years.[6]

Distribution

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The species has the largest geographic range of all slow loris species[13]and is native toBangladesh,Northeast India,andIndochina(Cambodia,Laos,Burma,Vietnam,southernChina,andThailand).[6]It is the only nocturnal primate found in the northeast Indian states,[24]which includeAssam,Mizoram,Nagaland,Meghalaya,Manipur,andTripura.It is found in parts ofYunnanand in southwestGuangxiin China, and has been recorded in theChittagong Hill Tractsin Bangladesh. It is known from 24 protected areas in Vietnam, and is distributed across most of Thailand. In Burma, it has been reported fromBhamo,Sumprabum,Kindat,Chin Hills,Pathein,Thaungdaung,andPegu;populations in Laos have been recorded in the north, central, and southern portions of the country.[6]

The Bengal slow loris issympatric(shares its range) with the pygmy slow loris in the southeast of China, Vietnam, and Laos. The Bengal slow loris is also sympatric with the Sunda slow loris on thesouthern peninsula of Thailand.In 2001, Groves reported the existence ofhybridsbetween these two species in this region.[8]

Conservation

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See also:Conservation of slow lorises

Listed as "Data Deficient"as recently as 2006 on theIUCN Red List,the Bengal slow loris was evaluated in 2020 by theInternational Union for Conservation of Nature(IUCN) as endangered-a decision based solely on habitat loss due to lack of sufficient field data.[2][25]It is found within numerousprotected areaswithin its range. However,poachingandillegal loggingare rampant while conservation measures are not species-specific. The species can be found in at least 43 protected areas in Northeast India, 14 conservation areas in Laos, and 24 protected areas in Vietnam. It can be found atLawachara National Parkin Bangladesh, and 80% of its range in China is protected.[6]The species has been listed in Schedule I of the IndianWildlife Protection Act of 1972,[13][24]and in June 2007, it was transferred, along with all other slow loris species, toCITES Appendix I,which forbids international commercial trade.[26]

The most severe threats facing the species are thewildlife trade(trapping forexotic petsand use intraditional medicine) anddeforestation.Slash and burnagriculture has also resulted in the destruction of its habitat, and road construction is another factor in its decline. Hunting has been found to be most severe when nearby urban human populations increase.[6]Enhancing protection measures, enforcing current wildlife protection laws, and improving the connectivity between protected areas are factors considered critical to ensure the survival of this species.[11][27]

The species is commonly sold as a pet and to zoos throughout Southeast Asia. In Cambodia, it was reported in 2006 as one of the most common mammals found in shops and stalls, found in the hundreds and selling for US$0.85 to US$6.25. In the same year, it was found selling for US$2.50 to US$6.30 at bazaars in China (Mengla CountyinYunnan Province) and US$70 in Thailand. The Bengal slow loris is used in traditional medicine in all of these countries, selling for US$15 in Vietnam, and is also eaten in Vietnam.[6]The animal is predominantly used to prepare treatments for women after childbirth, stomach problems, healing wounds and broken bones, and in the treatment of sexually transmitted diseases. Primary users are wealthy to middle-class women in urban areas.[28]

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Throughout its geographic range, slow lorises are in serious decline. Their habitat has been seriously degraded, and growing human populations will add increasing pressure. In countries like Bangladesh, only 9% of the original forest cover was still present in 2000. In northeastern Cambodia, forests are being cleared at an increasing rate, with a loss of 6% of the natural forest between 1999 and 2000. Within those same years, Myanmar and Thailand lost 14% and 26% of their natural forest, respectively. In Vietnam, only 30% of the original forest cover remains due to the deforestation caused by theVietnam War,and only 10% of that includes closed-canopy forests. Habitat destruction remains rampant, and all slow loris populations within its borders are significantly depleted. Populations have been declaredlocally extinctin southernQuảng Nam Provinceand parts of the highlands, and the same is expected inSong ThanhandKon Cha Rangnature reserves.[6]

In India, dense forest canopy has been depleted by as much as 55% in some areas and is rapidly disappearing. As early as 1987, the Indo-China region had reportedly lost 75% of the natural habitat for slow lorises. In 1992, the population size was estimated between 16,000 and 17,000 individuals, based on available habitat; however, recent publications report that few individuals remain due to a reduced geographic range. The Bengal slow loris may be restricted to a few isolated populations and is in serious threat of becoming locally extinct in parts ofAssamandMeghalaya.InArunachal Pradesh,its population is declining and under threat.[6][25]

Population densityhas been estimated between 0.03 and 0.33 individuals per km2in Assam, India, according to a study published in 2006.[6][13]A survey in 2007 at theThrisna Wildlife SanctuaryandSipahijola Wildlife Sanctuaryin Tripura, India, yielded an encounter rate of 0.22 individuals/km, with seven of nine sightings occurring within 1.71 km2(0.66 sq mi) and most of the animals found at a height of 8–15 m (26–49 ft) and near the interior of wet, deciduous forest.[13]In 2008, thespecies abundancewas measured at 0.18 individuals/km atGibbon Wildlife Sanctuaryin Assam.[25]

Since the 1990s, China's forests have declined significantly. InYunnanandGuangxiprovinces,primary forestsare few and isolated, andsecondary forestshave been severely degraded. Yunnan has lost 42% of its forests and 2,000 or less slow lorises remain. In Guangxi, the Bengal slow loris is nearly extinct. It has been extirpated inNingming Countyand only a few individuals are left inJingxi,Longzhou,andPingxiang.[6]

References

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  1. ^abGroves 2005,pp. 122–123.
  2. ^abNekaris, K.A.I.; Al-Razi, H.; Blair, M.; Das, N.; Ni, Q.; Samun, E.; Streicher, U.; Xue-long, J.; Yongcheng, L. (2020)."Nycticebus bengalensis".IUCN Red List of Threatened Species.2020:e.T39758A179045340.doi:10.2305/IUCN.UK.2020-2.RLTS.T39758A179045340.en.Retrieved19 November2021.
  3. ^UNEP-WCMC."CITES species database:Nycticebus bengalensis".UNEP-WCMC Species Database.Retrieved3 February2011.[permanent dead link]
  4. ^Groves 2005,p. 122.
  5. ^abcGroves 2001,p. 99.
  6. ^abcdefghijklmnopqrsManagement Authority of Cambodia (3–15 June 2007).Notification to Parties: Consideration of Proposals for Amendment of Appendices I and II(PDF).Netherlands: CITES. p. 31. Archived fromthe original(PDF)on 28 February 2011.Retrieved9 January2011.
  7. ^Chen et al. 2006,pp. 1197–1198.
  8. ^abcdePan, D.; Chen, J. H.; Groves, C.; Wang, Y. X.; Narushima, E.; Fitch-Snyder, H.; Crow, P.; Jinggong, X.; et al. (2007). "Mitochondrial control region and population genetic patterns ofNycticebus bengalensisandN. pygmaeus".International Journal of Primatology.28(4): 791–799.doi:10.1007/s10764-007-9157-1.S2CID35725257.
  9. ^abNekaris et al. 2010,p. 157.
  10. ^abOsman Hill 1953,p. 160.
  11. ^abRadhakrishna, S.; Goswami, A. B.; Sinha, A. (2006). "Distribution and conservation ofNycticebus bengalensisin northeastern India ".International Journal of Primatology.27(4): 971–982.doi:10.1007/s10764-006-9057-9.S2CID6679294.
  12. ^abSmith et al. 2008,pp. 159–160.
  13. ^abcdeSwapna, N.; Gupta, Atul; Radhakrishna, Sindhu (2008)."Distribution survey of Bengal Slow LorisNycticebus bengalensisin Tripura, northeastern India "(PDF).Asian Primates Journal.1(1): 37–40. Archived fromthe original(PDF)on 2011-07-27.
  14. ^Smith et al. 2008,p. 159.
  15. ^Osman Hill 1953,p. 162–163.
  16. ^Hagey, Fry & Fitch-Snyder 2007,p. 253.
  17. ^Hagey, Fry & Fitch-Snyder 2007,p. 263.
  18. ^Hagey, Fry & Fitch-Snyder 2007,p. 269.
  19. ^Francis 2008,p. 261.
  20. ^abPliosungnoen, M.; Gale, G.; Savini, T. (2010). "Density and microhabitat use of Bengal slow loris in primary forest and non-native plantation forest".American Journal of Primatology.72(12): 1108–1117.doi:10.1002/ajp.20875.PMID20938966.S2CID31261833.
  21. ^Nekaris et al. 2010.
  22. ^Swapna, N.; Radhakrishna, S.; Gupta, A.K.; Kumar, A. (2010). "Exudativory in the Bengal slow loris (Nycticebus bengalensis) in Trishna Wildlife Sanctuary, Tripura, northeast India ".American Journal of Primatology.72(2): 113–121.doi:10.1002/ajp.20760.PMID19937974.S2CID23726143.
  23. ^abcdefSmith et al. 2008,p. 160.
  24. ^abNandini, Rajamani; Kakati, Kashmira; Ved, Nimesh (2009)."Occurrence records of the Bengal Slow Loris (Nycticebus bengalensis) in northeastern India "(PDF).Asian Primates Journal.1(2): 12–18. Archived fromthe original(PDF)on 2012-03-03.
  25. ^abcDas, Nabajit; Biswas, J; Das, J.; Ray, P. C.; Sangma, A.; Bhattacharjee, P. C. (2009)."Status of Bengal Slow LorisNycticebus bengalensis(Primates: Lorisidae) in Gibbon Wildlife Sanctuary, Assam, India ".Journal of Threatened Taxa.1(11): 558–561.doi:10.11609/jott.o2219.558-61.ISSN0974-7907.
  26. ^Nekaris, K.A.I.; Jaffe, S. (2007)."Unexpected diversity of slow lorises (Nycticebus spp.) within the Javan pet trade: implications for slow loris taxonomy ".Contributions to Zoology.76(3): 187–196.doi:10.1163/18759866-07603004.S2CID45718454.Archived fromthe originalon 24 July 2011.Retrieved9 January2011.
  27. ^Karanth, Krithi K.; Nichols, James D.; Hines, James E. (2010). "Occurrence and distribution of Indian primates".Biological Conservation.143(12): 2891–2899.doi:10.1016/j.biocon.2010.02.011.
  28. ^Starr, C.; Nekaris, K. A. I.; Streicher, U.; Leung, L. (2010)."Traditional use of slow lorisesNycticebus bengalensisandN. pygmaeusin Cambodia: an impediment to their conservation "(PDF).Endangered Species Research.12(1): 17–23.doi:10.3354/esr00285.Archived(PDF)from the original on 2020-12-02.Retrieved2020-01-27.

Literature cited

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