Distinct demographic histories associated with elevational ranges of two giant flying squirrel species in Taiwan

Geographic and environmental isolation affect genetic differentiation. While their relative importance has been investigated in many species, it is unclear whether closely related species on the same island would show similar patterns of within-species population structure. In this study, we use demographic and environmental modeling to explore factors affecting genetic diversification by contrasting a closely related pair of species, the giant flying squirrels Petaurista lena and Petaurista grandis in Taiwan, with similar life histories but different elevational ranges. Both species exhibit north-south differentiation, with little association between genetic variation and environmental characteristics after accounting for neutral factors. Interestingly, the two species exhibit very different demographic histories. P. lena experienced an early north-south divergence (~163 thousand years ago) with higher post-divergence gene flow, larger population size, and higher genetic variation. This demographic pattern coincides with the generally larger suitable area for P. lena in the past. In contrast, P. grandis had a more recent north-south differentiation (~46 thousand years ago) and smaller population size, with the northern population experiencing a strong bottleneck. The demographic pattern likely contributed to the stronger north-south divergence in P. grandis, whose relatively recent north-south divergence and lower genetic variation may be associated with its smaller historical suitable area than P. lena. Together, we showed that species with similar life histories on the same island may exhibit similar north-south divergence patterns reflecting the geography of the island, yet the demography might vary due to their respective elevational ranges, reactions to past climate change, and potential competitive exclusion.