No species barriers: Langurs form unusual alliance in the wild

If the latest research by primatologists in the Western Ghats is any indication, visitors to the Anamalai Tiger Reserve may be in for an unexpected treat. Not only will they see recognized langur species such as the Nilgiri langur and Hanuman langur, but they may also spot langurs of varying colors and shapes. The study points to the possibility of hybrid individuals similar to the Nilgiri langur assemblage (johnnypithecus) and tufted gray langur (ancient ape, also known as Hanuman’s langur) in some parts of the reserve. The authors believe this phenomenon is the result of hybridization between the two langur species observed in the region over a considerable period of time.

Primatologist Mewa Singh, distinguished professor at the University of Mysore and co-author of the study, said hybridization between closely related species is not uncommon in the wild, although it is rare in mammals. relatively rare. He said the Nilgiri langurs and tufted gray langurs were showing signs of interbreeding in mixed-species groups. However, according to him, this concern is due to the fact that there are no signs of the establishment of a new species, which should have happened considering that hybridization has been going on for some time. This casts doubt on the hybrid’s ability to survive or reproduce, he explained. He noted that this remains largely a possibility until detailed genetic studies determine it.

Various shades of brown

A mixed-species colony is defined as a group of independently moving animals from multiple neighboring species that interact with each other, the paper said. There are many factors that contribute to this organization, including anti-predation, mate search, increased movement efficiency, and human factors, among others.

This study aimed to explore the physical characteristics and social organization of a mixed-species assemblage of Nilgiri langurs and tufted gray langurs found in the Anamalai Tiger Reserve at an altitude ranging from 300 to 800 meters above sea level. Lots of mixed morphology types. A morphotype refers to any different type of individuals of the same species in a population. The research paper states that while dark gray langurs are observed at lower altitudes, light brown variants or variants are observed at mid-elevations, while dark brown variants are more prevalent at higher altitudes.

It is important to note the different habitat preferences of Hanuman and Nilgiri langurs. Hanuman’s langur usually lives at lower altitudes, inhabiting the eastern slopes of hills characterized by dry deciduous forest and shrubland. In contrast, Nilgiri langurs prefer relatively moist areas on ridges, valleys and western slopes. However, mixed species associations of these two species occur in transitional areas between these different habitats.

The study found that mixed species group sizes were larger than those of both Nilgiri and Hanuman langurs, with these groups containing many adult males and females. This is another significant difference from the Nilgiri langur group, as they almost never form multi-male groups. Nilgiri langurs are usually divided into single-male, multi-female groups, of which about 60% are adults and the remainder are subadults and juveniles. Honnavalli N. Kumara, chief scientist at the Salim Ali Center for Ornithology and Natural History, who participated in the study, stressed that no multi-male groups were observed.

It is not uncommon to find mixed species tissue in monkeys. Singh noted similar observations in parts of Bhutan and northeastern India. Anwaruddin Choudhury, a naturalist who specializes in wildlife in northeastern India, recalled in a 2008 paper the hybrid langurs he saw during a visit to south-central Bhutan.natural hybridization (Rough-skinned ape)and golden langurs (Trachypithecus galli) was found in Dzongkha Zhegang (district). He writes: The hybrid langurs observed near the town of Zhemgang look like golden langurs from a distance, but upon closer inspection various shades of gray become apparent. There is no uniform pattern. I saw an almost pure golden langur phenotype in the same group, one with a gray back and another with gray flanks, and one that looked like a hooded langur but with lighter of gray.

Similarity, habitat proximity as causes

Kumara believes the similar genus and similar body size of the two langurs may have helped mitigate their mixing in the Anamalai hybrid. Additionally, the overlap in their habitats is thought to be a contributing factor. Previous research highlights that minimal competition for food resources further encourages mixed-species association. As stated in the paper, both species of langurs feed primarily on leaves, with Nilgiri langurs showing a greater preference for leaves than Hanuman langurs.

Kumara stressed that this research is of vital significance to protect the declining Nilgiri langurs. Listed as Vulnerable on the IUCN Red List of Threatened Species, forest fragmentation, human intervention, poaching, etc. are listed as some of the threats to this species restricted to the Western Ghats.

In a paper published in 2023, Singh, Kumara and team assessed the distribution, social organization and management of Nilgiri langurs in the Western Ghats of Nilgiri-Brahmagiri, Siruvani, A Five important groups are found in five different areas of Namale-Palambikulam, Cardamom Hills. . The paper points out that the geographical distribution area of ​​these five populations is 9976 square kilometers, of which the suitable habitat area of ​​this species is about 7718 square kilometers, including evergreen forest, mountain forest, moist deciduous forest, dry deciduous forest and artificial forest.

Kumara said there is a misconception that Nilgiri langurs are widespread and common, which is far from the truth, and if hybridization occurs, there is an urgent need to take steps to protect the original genetic pool of the species. Genetic research into hybridization is ongoing, and researchers hope that through the combined efforts of all stakeholders, the original species can be preserved.

Read more: Golden langurs threatened by lack of suitable habitat

Banner image: Mixed morphotype of Nilgiri langur and Hanuman langur. Genetic studies are ongoing to establish hybridization between the two species. Photo by Santanu Mahato.