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

Melanie B Prentice,Jeff Bowman,Kamal Khidas,Dennis L Murray,Jeffrey R Row,Erin L Koen,Paul J Wilson

doi:10.1002/ece3.2945

Abstract

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.

Highlights

Island populations are extreme examples of genetic divergence caused by geographical and landscape barriers to gene flow, where large bodies of water inhibit the immigration of new individuals from the mainland (MacArthur & Wilson, 1967)
Some characteristics appear to evolve faster than expected on islands because high standing adaptive genetic variation is believed to be the most influential mechanism for adaptation (Barrett & Schluter, 2008), and island populations generally exhibit low levels of genetic diversity (Nei et al, 1975). Such fast-paced evolution on islands is likely determined by strong selective pressures for specific traits, driven by the highly divergent environments and community structures often encountered on island landscapes that are necessary to overwhelm the effects of genetic drift
While it is true that the lower genetic diversity of the insulin-like growth factor-1 (IGF-1) locus on island compared to mainland groups of lynx could be the result of genetic drift, selection for fewer, but more favorable alleles on islands are better supported by our cumulative data

Summary

| INTRODUCTION

Island populations are extreme examples of genetic divergence caused by geographical and landscape barriers to gene flow, where large bodies of water inhibit the immigration of new individuals from the mainland (MacArthur & Wilson, 1967). Some characteristics appear to evolve faster than expected on islands because high standing adaptive genetic variation is believed to be the most influential mechanism for adaptation (Barrett & Schluter, 2008), and island populations generally exhibit low levels of genetic diversity (Nei et al, 1975) Such fast-paced evolution on islands is likely determined by strong selective pressures for specific traits, driven by the highly divergent environments and community structures often encountered on island landscapes that are necessary to overwhelm the effects of genetic drift. Given the preceding evidence that lynx on Cape Breton Island have diverged phenotypically from individuals on the mainland, it is reasonable that both genetic drift and selection have contributed to their evolution and differentiation since their establishment on the Island, and perhaps on Newfoundland as well We used both neutral microsatellites and one non-neutral (functional) genetic marker (insulin-like growth factor-1; IGF-1) to evaluate the influence of genetic drift and natural selection on insular and mainland populations of Canada lynx in eastern Canada. If the gene is under selection or linked to a nearby locus under selection in lynx, we predicted that we would observe a relationship between common IGF-1 alleles found in lynx on Cape Breton Island and morphology

| METHODS

Findings

| DISCUSSION

| CONCLUSIONS