In Borneo, a ‘hybrid monkey’ worries researchers

An unidentified monkey seen in Borneo is likely the offspring of a proboscis monkey and a silver langur, according to a new study. These two species, which share the same habitat, are genetically distant. Researchers are concerned that this type of forced hybridization is multiplying in this region where human activities are taking up more and more space.

Interspecific hybridization in primates is common. For example, the northern pig-tailed monkeys (leonine monkey) and southern braids (nemestrine monkey) occasionally cross in parts of Thailand. However, these species involved are generally similar and belong to the same evolutionary group or genus.

As part of a study published in the International Journal of Primatology, a team of researchers presents several pieces of evidence that attest to a possible hybridization event In between nasalis larvatus (proboscis) and Trachypithecus cristatus (Silver Langur) at Lower Kinabatangan Wildlife Sanctuary, Sabah. However, these two species do not belong to the same genus.

A rare event in nature

Researchers rely solely on photographic evidence. In these photos, a mature female seen as a young three years earlier was carrying a baby. The hybrid monkey was reportedly seen near the Kinabatanga River in Borneo, where populations of proboscis monkeys and silver langurs overlap.

As a rule, these matings do not produce viable offspring, hence the interest of these observations. It is possible that this mother was breastfeeding (taking care of another female’s baby), but the photos show swollen breasts (associated with lactation), indicating that the offspring were really yours.

Physically, the two species differ widely. Adult proboscis monkeys have pink faces with elongated noses, while adult silver langurs display black faces with shorter, flattened noses. The first ones are also bigger. A male proboscis can actually measure up to 76 cm long and regret from 20 to 24kgwhile the langurs do not exceed the 56cm long and the 7kg on the scale. However, the macaca here presents characteristics of these two species.

A family of proboscis monkeys in a tree in Borneo. Credits: USE
A group of silver langurs. Credits: Anup Shah

Proboscis monkeys in the process of imposing themselves?

Both species live in groups consisting of a dominant male. The others are thus forced to leave once mature to create or take over another group. However, the decline of its habitat limits your scatter abilities.

Based on these photographic observations, the researchers believe that male proboscis monkeys mate with female silver langurs. These males could actually use their larger size to kick out smaller competitors and thus take control of the langur groups. The researchers suspect the presence of several mixed groups in the area.

As fascinating as this discovery is, the researchers are concerned about it. It is truly tragic that these two species are finally forced to jostle together to share increasingly narrow stretches of forest surrounded by oil palm plantations. Feeding and mating opportunities are increasingly scarce today, which could ultimately harm both species.

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