Is the low population size of the Sichuan Jay reflected in their genetic make-up?
Somewhere in the mountains of western China you might stumble upon a peculiar species: the Sichuan Jay (Perisoreus internigrans). Little is known about this corvid. A survey between 1999 and 2004 estimated about 1 individual per km2 in Jiuzhaigou (and the density was even lower in Zhuoni). These low densities are probably the result of habitat fragmentation: large patches of pristine forest have been removed. Moreover, the habitat of the Sichuan Jay has been influenced by the Pleistocene ice ages when forests were fragmented by advancing ice sheets. Taken together, we can expect that these events led to a significant reduction in population size and hence genetic diversity. A recent study in the journal Conservation Genetics put this expectation to the test.
Kai Song and his colleagues collected samples from 58 Sichuan Jays and compared their DNA with 205 Siberian Jays (P. infaustus) from Sweden and Russia. As explained above, the researchers expected a clear reduction in genetic diversity in the Sichuan Jays. Suprisingly, this was not the case. Both species showed similar levels of genetic diversity, despite the more restricted range of the Sichuan Jay.
Moreover, the populations of Sichuan Jay showed clear population structure, separating into three clear clusters (see figure below). Unfortunately, the sampling locations of these birds have been lost, so it is currently not possible to relate this structure to particular geographical locations.
Does the high level of genetic diversity mean that we should not worry about the Sichuan Jay which is currently considered “vulnerable” by the IUCN? Not necessarily, the analyses were based on microsatellites, which are known to be very variable. It is thus possible that this study overestimated the amount of genetic diversity. In addition, the clear separation into three clusters suggests that the populations of Sichuan Jays are highly fragmented into small populations. This might make them more vulnerable to environmental changes.
Habitat loss seems to be the most important threat for this Chinese bird species. To prevent further population decline targeted habitat restoration is key. The protection and expansion of virgin conifer forest will not only benefit the Sichuan Jay, but numerous other species, such as Chinese Grouse (Tetrastes sewerzowi) and Sichuan Wood Owl (Strix davidi).
Song, K., Halvarsson, P., Fang, Y., Barnaby, J., Germogenov, N., Sun, Y., & Höglund, J. (2020). Genetic differentiation in Sichuan jay (Perisoreus internigrans) and its sibling species Siberian jay (P. infaustus). Conservation Genetics, 21: 319–327.