Selection and drift influence genetic differentiation of insular Canada lynx (Lynx canadensis) on Newfoundland and Cape Breton Island

Island populations have long been important for understanding the dynamics and mechanisms of evolution in natural systems. While genetic drift is often strong on islands due to founder events and population bottlenecks, the strength of selection can also be strong enough to counteract the effects of drift. Here, we used several analyses to identify the roles of genetic drift and selection on genetic differentiation and diversity of Canada lynx (Lynx canadensis) across eastern Canada, including the islands of Cape Breton and Newfoundland. Specifically, we assessed whether we could identify a genetic component to the observed morphological differentiation that has been reported across insular and mainland lynx. We used a dinucleotide repeat within the promoter region of a functional gene that has been linked to mammalian body size, insulin-like growth factor-1 (IGF-1). We found high genetic differentiation at neutral molecular markers but convergence of allele frequencies at the IGF-1 locus. Thus, we showed that while genetic drift has influenced the observed genetic structure of lynx at neutral molecular markers, natural selection has also played a role in the observed patterns of genetic diversity at the IGF-1 locus of insular lynx.

Isolation of peripheral populations of Canada lynx (Lynx canadensis)

Landscape barriers to gene flow, such as rivers, can affect animal populations by limiting the potential for rescue of these isolated populations. We tested the riverine barrier hypothesis, predicting that the St. Lawrence River in eastern Canada would cause genetic divergence of Canada lynx (Lynx canadensis Kerr, 1792) populations by restricting dispersal and gene flow. We sampled 558 lynx from eastern Canada and genotyped these at 14 microsatellite loci. We found three genetic clusters, defined by the St. Lawrence River and the Strait of Belle Isle, a waterway separating Newfoundland from mainland Canada. However, these waterways were not absolute barriers, as we found 24 individuals that appeared to have crossed them. Peripheral populations of lynx are threatened in parts of Canada and the USA, and it is thought that these populations are maintained by immigration from the core. Our findings suggest that in eastern North America, rescue might be less likely because the St. Lawrence River restricts dispersal. We found that ice cover was often sufficient to allow lynx to walk across the ice in winter. If lynx used ice bridges in winter, then climate warming could cause a reduction in the extent and longevity of river and sea ice, further isolating these peripheral lynx populations.