- Scientists sequencing the genes of captive Malaysian white-handed gibbons, Hylobates lar lar, have discovered two separately evolving populations, in the north and south of Peninsular Malaysia.
- For the past thousands of years, the northern and southern groups have been geographically isolated and evolving independently, the scientists say.
- Now, their genetic distance is large enough that they could potentially be two distinct subspecies, according to the scientists, who sequenced a fast-evolving segment of mitochondrial DNA from the captive gibbons.
- For researchers looking to reintroduce captive gibbons back into the wild, focusing on that particular segment is a powerful method for pinpointing the population an animal originated from.
If you get yourself a map of Peninsular Malaysia and color in all the areas in which the Malaysian subspecies of white-handed gibbons (Hylobates lar lar) live, you’ll find a blank spot across the states of Kelantan, northern Perak and northern Terangganu.
Here, in this stretch of land between the Muda and Perak rivers, an entirely different species dominates: black-handed gibbons (Hylobates agilis). Their presence splits the white-handed gibbons, which are otherwise scattered across the whole peninsula, into two populations: a northern and southern one.
For the past thousands of years, the northern and southern populations, geographically isolated from each other, have been evolving independently. Now, scientists sequencing the genes of these gibbons have found they have grown so genetically different, they could potentially qualify as two distinct subspecies.
The researchers, whose study was published in ZooKeys, sequenced a section of mitochondrial DNA each from 12 captive white-handed gibbons from Peninsular Malaysia’s National Wildlife Rescue Centre in a routine genetic assessment conducted before animals are released back into the wild.
For scientists looking to translocate and reintroduce captive gibbons into the forest, knowing the finer details like which population a particular animal originated from can help reduce interbreeding and ensure the different populations stay healthy in the long run, co-author Jeffrine Rovie-Ryan, a researcher at the University of Malaysia, Sarawak, told Mongabay.
“Separate populations should be managed separately,” Rovie-Ryan said. “If you mix animals from different populations, that will contaminate the gene pool, making the animals more susceptible to diseases.”
The researchers had expected a straightforward result identifying which subspecies the gibbons belonged to, but instead discovered unusual mutations in the DNA. Comparing this data against sequences from white-handed gibbons of other subspecies obtained from the genetic database GenBank, they found the genetic distance between the northern and southern populations to be on par with the genetic distance between H. l. lar and other H. lar subspecies, signifying the two populations could potentially be two different subspecies.
The fragment of DNA, known as the complete control region, was chosen for being the fastest-evolving segment in mitochondrial DNA for white-handed gibbons, Rovie-Ryan said.
“It’s just a short fragment, but it is very powerful,” he said, adding that if the researchers had chosen a slower-evolving segment, it might not have been enough to differentiate between different species and subspecies — let alone something as specific as different populations within the same subspecies.
Sequencing the complete control region to differentiate between populations isn’t a method that works for all species of animals, however. “We did a few studies on Malayan pangolins [Manis javanica], but we couldn’t find any significant differences [in complete control regions] between two different populations,” Rovie-Ryan said. “Luckily, when we used this segment in gibbons, we could see a differentiation.”
In cases where it doesn’t work, researchers can resort to whole genome sequencing, where they map out the entire DNA sequence (including mitochondrial DNA) of a cell to search for genetic differences — though that requires more computational power, and tends to be costlier.
Rovie-Ryan said confirming whether the northern and southern populations of gibbons ought to be classified as separate subspecies would require more samples, from wild individuals instead of only captive ones. Sequencing more DNA segments apart from the complete control region, and even whole genome sequencing, would also give greater clarity.
“We also need to look at whether the [northern and southern] populations mix with each other at all,” he added.
“Is there a gradient, or are they totally separate? If there’s a gradient, it’s possible they’re not different subspecies, but [exhibiting] variations within a big population,” he said.
Banner image of white-handed gibbon (Hylobates lar). Image by JJ Harrison via Creative Commons (CC BY 3.0)
Citation:
Gani, M., Rovie-Ryan, J. J., Sitam, F. T., Kulaimi, N. A. M., Zheng, C. C., Atiqah, A. N. … Mohammed, A. A. (2021) Taxonomic and genetic assessment of captive white-handed gibbons (Hylobates lar) in Peninsular Malaysia with implications towards conservation translocation and reintroduction programmes. ZooKeys, 1076, 25-41. doi:10.3897/zookeys.1076.73262
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Malaysia’s white-handed gibbons may be two subspecies, not one, study shows
Source: Trends News
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