Choosy Snowcocks: How habitat preference can affect genetic population structure

Genetic study reveals striking differences in population structure for two snowcock species in the Himalayas.

The Tibetan Plateau houses two species of snowcock: the Tibetan Snowcock (Tetraogallus tibetanus) and the Himalayan Snowcock (T. himalayensis). These partridge-like birds occur in the mountain ranges around the plateau, but occupy slightly different habitats. The Tibetan Snowcock prefers high-altitude areas (above 3000 meters) with dwarf shrubs, while the Himalayan Snowcock can be found in low-elevation regions that are drier and warmer. These differences in distribution can affect their genetic make-up. A recent study in the journal Avian Research used several microsatellites and a mitochondrial marker to probe the population genetic patterns of these species.

Himalayan Snowcock

Himalayan Snowcock © Subharanjan Sen | Oriental Bird Club Image Database

 

 

Population Structure

The genetic analyses by Bei An and colleagues revealed some interesting differences between the two species. Populations of Himalayan Snowcock showed a “divergent and structured” pattern whereas there was no clear phylogeographic pattern in the Tibetan Snowcock. The researchers speculate that this difference is due to the distinct habitat preferences of these snowcocks.

The high-altitude lifestyle of the Tibetan Snowcock might render it more resilient to extreme cold. Hence, this species might have been affected less by the glacial cycles of the Pleistocene. Populations did not have to survive the cold periods in separate refugia and so do not exhibit any clear population structure. The Himalayan Snowcock, on the other hand, occurred at lower altitudes where populations were fragmented by the waxing and waning of the Pleistocene ice sheets. This explanation makes intuitive sense, but will need to be tested (for example with some ecological niche modelling).

Tibetan_Snowcock

Tibetan Snowcock © Donald Macauley | Wikimedia Commons

 

Hybridization

The mitochondrial marker indicated that Tibetan and Himalayan Snowcock are clearly distinct. The haplotype network, however, uncovered an intruiging insight. One haplotype (H9) was shared by both species. This finding suggests that there might be occasional hybridization. Indeed, both species co-occur in some regions, such as the Kunlun Mountains and the Qilian Mountains. More dense sampling is required to investigate whether these species actually interbreed.

snowcocks

The mitochondrial marker shows that both species are clearly distinct. However, one haplotype (H9 in the network) suggests that they might interbreed. From: An et al. (2020) Avian Research

References

An, B., Zhang, L., Wang, Y., & Song, S. (2020). Comparative phylogeography of two sister species of snowcock: impacts of species-specific altitude preference and life history. Avian Research, 11(1), 1.

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