A recent study revealed a troubling trend among the wild monkey population in Bangladesh’s northeastern forests. The study, conducted by the German Primate Centre, unveiled a concerning tendency of hybridization between Phayre’s langurs (Trachypithecus phayrei) and capped langurs (Trachypithecus pileatus), listed as critically endangered and endangered, respectively, within Bangladesh by IUCN.
This hybridization of the endangered primates, which researchers of the study say is caused by habitat loss due to deforestation and other human interferences, could push them to extinction in a few generations.
“Bangladesh’s langur populations are small and isolated, limiting gene flow. This hybridization in restricted populations heightens their extinction risk. Furthermore, our laws primarily protect pure langurs, leaving hybrids unprotected. If hybrids persist into future generations, we’ll face tough decisions about their role in our ecosystem,” Tanvir Ahmed, the study’s lead researcher, told Mongabay.
Monirul H. Khan, a professor at Jahangirnagar University’s Zoology Department, agreed with Tanvir and said that the significance of interbreeding is that these langurs don’t survive for a long time.
“They are usually born infertile. So the population of langur will gradually decrease,” he said.
The study, published in the International Journal of Primatology, recently found that out of 98 langur groups observed, eight comprised both Phayre’s and capped langurs.
“We analyzed genetic samples of the species in the lab and confirmed one case of hybridization. This langur had a capped langur mother and a Phayre’s langur father. Another female with a hybrid appearance showed signs of motherhood, indicating that at least female hybrids are fertile and give birth to young,” Tanvir said.
“The genetic characteristics of a distinct species tend to become most threatened when their hybrid females can reproduce. Fertile hybrid females threaten to bring the two species closer together as the offsprings begin to mix characteristics. That is exactly what could be happening to them,” he said.
The research shows that the ‘spectacled’ Phayre’s langurs and the capped langurs, with their distinctive shock of black fur on their heads, are under threat of losing their distinct genetic makeup to hybridization.
Researchers conducted the study over five years, between 2018 and 2023, in six forests in northeastern Bangladesh — Lawachara National Park, Satchari National Park, Rema-Kalenga Wildlife Sanctuary, Rajkandi Reserve Forest, Patharia Hill Reserve Forest and Atora Hill Reserve Forest.
The study involved field surveys for 92 days between March 2018 and April 2019 and from July to December 2022, employing three trained local eco-guides to monitor the mixed-species groups until October 2023.
Why hybridization is a concern
The study shows that, although it’s relatively rare, hybridization among primates is an escalating concern worldwide, often driven by habitat loss and fragmentation. It serves as a stark reminder of the significant impacts of human activity on biodiversity. The situation in Bangladesh gradually becoming more common emphasizes the urgent need for strong conservation efforts.
The study mentions how hybridization is a vital indicator of ecological change, raising serious concerns about species’ genetic health. Tanvir added that this study is groundbreaking, as it documents the first hybridization incidents among these langurs in Bangladesh and their entire distribution range.
Hybrids being fertile could lead to the extinction of the parent species. “Additionally, mixing species can enable the spread of diseases between previously unconnected populations, posing risks to both wildlife and human health, since these animals are often hunted and traded,” said Sabit Hasan, a researcher of the study.
The study blamed human activities such as deforestation, habitat fragmentation, hunting and trapping of primates as some of the causes that can increase the risk of such hybridization.
“The existence of fertile hybrids is particularly alarming because it suggests that gene flow between these two endangered species could irreversibly affect their future genetic composition,” Tanvir said.
Primates of Bangladesh
Ten of the 121 mammal species found in Bangladesh are primates. According to the hybridization study, Bangladesh is home to less than 500 Phayre’s langurs and 600 capped langurs.
The Phayre’s langur has a brown to grey-brown back, white fur on its belly and face, and a “spectacled” appearance due to wide white rings around its eyes. Its face and extremities are black, and it has long hair on its head that points backward. Additionally, its tail is longer than its body and has a tuft of dark hair at the tip.
The capped langur is known for its distinctive crown of long, erect hairs on its head. It has a black face, grey to blackish-grey fur on top, and brownish-yellow or orange fur below, with the distal half of its tail being blackish.
The study suggested the government prioritize habitat preservation and create corridors to connect isolated primate populations, facilitating natural langur dispersal.
“If we don’t take action now, we risk losing not just two monkey species but also a vital part of Bangladesh’s biodiversity,” Tanvir said.
Citation:
Ahmed, T., Hasan, S., Nath, S., Biswas, S. … Roos, C. (2024). Mixed-Species Groups and Genetically Confirmed Hybridization Between Sympatric Phayre’s Langur (Trachypithecus phayrei) and Capped Langur (T. pileatus) in Northeast Bangladesh. International Journal of Primatology. doi:10.1007/s10764-024-00459-x
This article by Mohammad Al-Masum Molla was first published by Mongaby.com on 25 October 2024. Lead Image: The genetically confirmed hybrid (right) with its capped langur mother at Satchari National Park. Image by Harish Debbarma.
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