Silvery Lutung
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The silvery lutung (''Trachypithecus cristatus''), also known as the silvered leaf monkey or the silvery langur, is an
Old World monkey Old World monkeys are primates in the family Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (genus '' Papio''), red colobus (genus '' Piliocolob ...
. It is
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
, living in coastal,
mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...
, and riverine forests in
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
,
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
,
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
, as well as in parts of the southwestern
Malay Peninsula The Malay Peninsula is located in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The area contains Peninsular Malaysia, Southern Tha ...
, the
Natuna Islands Natuna Regency is an islands regency located in the northernmost part of the Province of Riau Islands, Indonesia. It contains at least 154 islands, of which 127 of them are reported as uninhabited. This archipelago, with a land area of 1,978.4 ...
, and other nearby islands. It is the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
of its
species group In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
.


Description

The silvery lutung is a medium-sized
monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, co ...
with a long, non-
prehensile Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origin ...
tail. It has grey-tipped, dark brown or black fur, giving it a uniform silvery appearance. Unlike some related species, there are no paler markings on the face or body, except for a patch of whitish hair on the groin of females. A crest of fur runs along the top of the head, and the hair on the cheeks is long, often obscuring the ears. The hands and feet are hairless, with dark-coloured skin, and have opposable thumbs and toes. Females range from in head-body length, with an average weight of and a tail length of . Males are slightly larger, from in length, with an average weight of and a tail length of . Like other langurs, the silvery lutung has a large three-chambered
stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
to digest the
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...
found in its
herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...
diet. This allows for
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
of food, and has some similarities with the stomach of
ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...
s. The
intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...
is unusually long, even compared to those of other langurs, and has several pouches along its length, which carry out further fermentation of plant matter. The teeth have grinding ridges and other modifications to allow the more efficient processing of tough leaves.


Distribution and habitat

The silvery lutung is found across
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
,
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
, and Java, as well as in parts of the southwestern
Malay Peninsula The Malay Peninsula is located in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The area contains Peninsular Malaysia, Southern Tha ...
, the
Natuna Islands Natuna Regency is an islands regency located in the northernmost part of the Province of Riau Islands, Indonesia. It contains at least 154 islands, of which 127 of them are reported as uninhabited. This archipelago, with a land area of 1,978.4 ...
, and other nearby islands. It inhabits
mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...
swamps and nearby forest regions and generally avoids travelling far from coasts or rivers.


Taxonomy

The number and identity of subspecies of the silvery lutung is currently debated. A 2008 analysis confirms the presence of only two subspecies: * ''Trachypithecus cristatus cristatus'' - Borneo, Sumatra, Natuna Islands * ''Trachypithecus cristatus selangorensis'' - Malay Peninsula The Malay Peninsula form has been subsequently elevated to a separate species, the Selangor silvered langur ''T. selangorensis'' However, some sources distinguish the silvery lutungs of the Natuna Islands as a separate subspecies, ''T. c. vigilans''.


Evolution

Genetic analysis has shown that the silvery lutung probably first evolved during a rapid speciation event that occurred between 0.95 and 1.25 million years ago, during which all the living species of the ''T. cristatus'' species group evolved. Because of the relative speed and diversity of this event, the species of the
group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...
are difficult to distinguish genetically, and there is some uncertainty as to which represents genuinely distinct species. However, the closest living relative of the silvery lutung may be the Javan lutung, although silvery lutungs have also been reported to produce hybrids with
Phayre's leaf monkey Phayre's leaf monkey (''Trachypithecus phayrei''), also known as Phayre's langur, is a species of Old World monkey native to South Asia and Southeast Asia, namely India, Bangladesh, and Myanmar. Populations from further east are now thought to b ...
, generally considered to belong to a different species group. Fossils of the species are known from the late
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
onwards and occupy the same geographic range as today. Some of these fossils had significantly larger cheek teeth than living animals, although they have not been assigned to a distinct subspecies.


Hybridization

In
Sabah Sabah () is a States and federal territories of Malaysia, state of Malaysia located in northern Borneo, in the region of East Malaysia. Sabah has land borders with the Malaysian state of Sarawak to the southwest and Indonesia's North Kalima ...
, Malaysia, silvery lutungs have been observed in mixed-
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
groups with
proboscis monkey The proboscis monkey or long-nosed monkey (''Nasalis larvatus'') is an arboreal Old World monkey with an unusually large nose (or proboscis), a reddish-brown skin color and a long tail. It is endemic to the southeast Asian island of Borneo an ...
s, and interspecific mating and a possible hybrid has been observed. The suspected hybrid was first sighted when it was a juvenile near the
Kinabatangan River The Kinabatangan River () is a river in Sandakan Division, in eastern Sabah, Malaysia. It is the second longest river in Malaysia, with a length of from its headwaters in the mountains of southwest Sabah to its outlet at the Sulu Sea, east of ...
in Malaysian Borneo. Researchers began monitoring the animal and analyzing photos of it as it matured which led to the conclusion it was an extremely rare phenomenon. Researchers say hybridization between closely related species is not unheard of, however, the offspring of two distantly related species is rarely observed in the wild, going on to say this particular hybrid is only the second time intergeneric hybridization (offspring resulting from the matings between different
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
) has been recorded in wild primates. Hybrid animals are often infertile, particularly with distantly related species, because it causes malfunctions in the
chromosomes A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most importa ...
. However, a photo of the animal as an adult showed her holding an infant that she appeared to be nursing. Researchers believe this may be a result of the two species being confined to a small patch of riverine forest due to
deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...
to plant
oil palm ''Elaeis'' () is a genus of palms, called oil palms, containing two species, native to Africa and the Americas. They are used in commercial agriculture in the production of palm oil. Description Mature palms are single-stemmed, and can gro ...
trees, a form of
habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...
, that created a segregated population of both species.


Behaviour and ecology

Silvery lutungs are diurnal, and travel in groups of around 9-40 individuals with one adult male and many adult females communally caring for infants. They rarely leave the trees, which provide them protection from ground-dwelling predators, and rapidly flee if threatened. Each group occupies a home range of , although these may overlap with those of neighbouring groups. During the day, individuals may travel up to through the forest, with some forming all-female subgroups that separate from the group containing the male. The entire group shelters in a single tree at night. The social structure of silvery lutungs is
matrilineal Matrilineality, at times called matriliny, is the tracing of kinship through the female line. It may also correlate with a social system in which people identify with their matriline, their mother's lineage, and which can involve the inheritan ...
and
harem A harem is a domestic space that is reserved for the women of the house in a Muslim family. A harem may house a man's wife or wives, their pre-pubescent male children, unmarried daughters, female domestic Domestic worker, servants, and other un ...
based. Females remain in the group for life, while males leave shortly after reaching adulthood, living in small groups of their own until they can take over an established harem. Within the group, males dominate the females, and females with young dominate those without. However, there is relatively little aggression within the group compared with some related species. Because group ranges often overlap, different groups frequently come into contact with one another. The adult male protects his group and territory from competing males, communicating his dominance to other males via vocalizations and fighting. In the absence of males, however, females from different groups are more likely to interact peacefully. The most serious conflicts occur when a male intrudes directly on the territory of another male, which may result in the intruder displacing the resident and taking control of the group. In many other primates, such a displacement would normally be followed by the male-killing any infants sired by his predecessor; although this may occur in silvery lutungs, it has not been directly observed and may be less common than in some other species. Although less vocal than other closely related species, silvery lutungs make at least thirteen different vocalisations, with the most common being used by adult males defending their territory. Other vocalisations express fear, anger, excitement, and satisfaction, in addition to various calls made by infants.


Diet

The silvery lutung is a specialist
folivore In zoology, a folivore is a herbivore that specializes in eating leaves. Mature leaves contain a high proportion of hard-to-digest cellulose, less energy than other types of foods, and often toxic compounds.Jones, S., Martin, R., & Pilbeam, D. (1 ...
, including a higher proportion of leaves in its diet than any other colobine monkey. Although it does also eat fruit, and some seeds and flowers, these comprise only 9% of the diet, and it is also able to feed on tougher and more mature leaves than any of its close relatives. Because of these differences, silvery lutungs do not normally live in the same parts of the forest as other monkeys. Where other species are found in the same area, silvery lutungs are more commonly found in the middle canopy of the forest, leaving the higher branches to monkeys with a more
frugivorous A frugivore ( ) is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance ...
diet.


Reproduction

Silvery lutungs breed year round, with no clear breeding season, although each female typically gives birth no more than once every 18 to 24 months. The female attracts the male by making side-to-side motions with her head, and copulation may occur several times during an encounter. Unusually, females have been reported to reach
menopause Menopause, also known as the climacteric, is the time when Menstruation, menstrual periods permanently stop, marking the end of the Human reproduction, reproductive stage for the female human. It typically occurs between the ages of 45 and 5 ...
in the wild and may survive up to nine years after giving birth. The female gives birth to a single young after a
gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...
period of 181 to 200 days. The young weigh about , measure about and are well developed, with a strong grip for holding onto the mother. Silvery lutungs are born with orange fur and with white hairless skin on the face, hands, and feet. The skin rapidly changes to the dark adult colour, but the fur does not reach the adult pattern for three to five months after birth. The young are cared for by females communally and are not
weaned Weaning is the process of gradually introducing an infant human or other mammal to what will be its adult diet while withdrawing the supply of its mother's milk. In the UK, weaning primarily refers to the introduction of solid foods at 6 mont ...
for 18 months, even though the biological mother stops lactating after just 12 months. The young are sexually mature almost as soon as they finish weaning, and, on average, females first give birth at 35 months of age. Silvery lutungs have lived up to 31 years in captivity.


Predators

Local predators able to feed on silvery lutungs include
leopard The leopard (''Panthera pardus'') is one of the five extant cat species in the genus ''Panthera''. It has a pale yellowish to dark golden fur with dark spots grouped in rosettes. Its body is slender and muscular reaching a length of with a ...
s,
tiger The tiger (''Panthera tigris'') is a large Felidae, cat and a member of the genus ''Panthera'' native to Asia. It has a powerful, muscular body with a large head and paws, a long tail and orange fur with black, mostly vertical stripes. It is ...
s, dholes, and some large snakes.
Binturong The binturong (''Arctictis binturong'') (, ), also known as the bearcat, is a viverridae, viverrid native to South Asia, South and Southeast Asia. It is uncommon in much of its range, and has been assessed as Vulnerable species, Vulnerable on th ...
s, and various other small carnivores are probably able to feed on infants.


Diseases

Silvery lutungs are unusually susceptible to human diseases, including
AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
, and have therefore been widely used in medical research.


Conservation

The silvery lutung is classified as Vulnerable on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
and is listed in Appendix II of
CITES CITES (shorter acronym for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of inte ...
. Its habitat is heavily threatened throughout its range by
logging Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidder, skidding, on-site processing, and loading of trees or trunk (botany), logs onto logging truck, trucksplantation Plantations are farms specializing in cash crops, usually mainly planting a single crop, with perhaps ancillary areas for vegetables for eating and so on. Plantations, centered on a plantation house, grow crops including cotton, cannabis, tob ...
s. It is also threatened by hunting for meat and by capture for the pet trade.


References


External links


BBC: Silvered Langur
*
Lotong Kelabu
{{Taxonbar, from=Q368754 silvery lutung Primates of Southeast Asia Mammals of Indonesia Mammals of Malaysia Primates of Borneo Near threatened animals Near threatened biota of Asia silvery lutung Taxa named by Thomas Stamford Raffles