Hybrid 'Mystery Monkey' Discovered in Borneo

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

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

Researchers began analyzing pictures of the monkey in a bid to determine what it was and found something extremely rare.

Findings suggest that the monkey is a cross between a proboscis monkey and a silvery langur. While 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, the study said. It is also only the second time intergeneric hybridization in wild primates has been recorded.

Hybridization between closely related species is not unheard of, however the offspring of two distantly related species is "rarely observed in the wild."

Proboscis monkeys and silvery langurs are not even part of the same genus—the two monkeys physically look very different from each other. Proboscis monkeys are larger than silvery langurs. They also have a light-colored face and large noses, while silvery 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 malfunctions in the chromosomes. However, a newer photograph suggest this female hybrid is fertile. The photograph show the hybrid monkey in 2020 with an infant and "swollen breasts," suggesting she was lactating.

Despite her apparent fertility, scientists are still concerned about what the hybridization could mean.

Co-author of the report and senior lecturer at the University of Science in Malaysia, Nadine Ruppert, told Newsweek that discovering the hybrid was alarming.

"Seeing this putative hybrid is per se not of concern to the balance of the ecosystem or the two species, however it is an alarming symptom of an ecosystem that already seems out of balance," she said.

Ruppert said the males of both species will usually disperse from their families upon adolescence to find mating opportunities. And, it seems that these mating opportunities have been "impeded" due to the fragmentation of their habitats, she said. This could explain how the hybrid came to be.

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

"In the long-run, one of these two threatened primate species may be displaced by the other from the area, whereby proboscis monkeys seem to be more dominant than the silver langurs," she said. "If habitat connectivity and dispersal opportunities will not be restored, it is also possible to see another hybrid soon, as mating between the two species seems to occur commonly in the area. But maybe this also was just a one-off random event, it's hard to tell without further in-depth studies and long-term monitoring."