Hybrid ‘Mystery Monkey’ discovered in Borneo

A hybrid “mystery monkey” has been discovered in Borneo, a new study in the International Journal of Primatology shows.

The rare primate was first spotted near the Kinabatangan River in Malaysian Borneo in 2017, when it was a baby.

The researchers began analyzing images of the monkey in an attempt to determine what it was and found something extremely rare.

The findings suggest that the monkey is a cross between a proboscis monkey and a silvery langur. Although these two species inhabit the same forest, they have very different characteristics and are distantly related.

This is the first time a hybrid of the two species has been recorded, according to the study. It is also only the second time intergeneric hybridization has been recorded in wild primates.

Hybridization between closely related species is not unknown, however the offspring of two distantly related species is “rarely observed in nature”.

Proboscis monkeys and silver langurs aren’t even part of the same genus: the two monkeys look very different from each other physically. Proboscis monkeys are larger than silver langurs. They also have a light-colored face and large noses, while silver langurs are black, with smaller noses; the hybrid monkey has characteristics of both.

Hybridization can often cause infertility, particularly with distantly related species, as it causes chromosome failures. However, a more recent photograph suggests that this female hybrid is fertile. The photograph shows the hybrid monkey in 2020 with a baby and “swollen breasts”, suggesting that it was nursing.

Despite its apparent fertility, scientists are still concerned about what hybridization might mean.

Report co-author and Senior Lecturer at the University of Science Malaysia, Nadine Ruppert, said news week that discovering the hybrid was alarming.

“Seeing this putative hybrid in itself is not a cause for concern for the balance of the ecosystem or the two species, however it is an alarming symptom of an ecosystem that already appears unbalanced,” he said.

Ruppert said that males of both species typically disperse from their families in adolescence to find mating opportunities. And it appears that these mating opportunities have been “prevented” due to the fragmentation of their habitats, she said. This could explain how the hybrid came to be.

Habitat fragmentation in this area has been largely caused by “anthropogenic development and agriculture,” Ruppert said, referring to human influence on the environment.

“In the long term, one of these two threatened primate species may be displaced by the other from the area, so proboscis monkeys appear to be more dominant than silver langurs,” he said. “If habitat connectivity and dispersal opportunities are not restored, it is also possible to see another hybrid soon, as mating between the two species seems to occur commonly in the area. But perhaps this too was just a single random event, It’s hard to say without more in-depth studies and long-term follow-up.”