Rapid Homogenization of Multiple Sources: Genetic Structure of a Recolonizing Population of Fishers

Abstract

Fishers (Martes pennanti) were extirpated from much of southern Ontario, Canada, prior to the 1950s. We hypothesised that the recent recolonization of this area originated from an expansion of the population in Algonquin Provincial Park, which historically served as a refuge for fishers. To test this hypothesis, we created a sampling lattice to encompass Algonquin and the surrounding area, and we collected contemporaneous DNA samples. We sampled fishers from each of 35 sites and genotyped them at 16 microsatellite loci. Using a Bayesian assignment approach, with no a priori geographic information, we inferred 5 discrete genetic populations and used genetic population assignment as a means to cluster sites together. We concluded that the Algonquin Park fisher population has not been a substantial source for recolonization and expansion, which has instead occurred from a number of remnant populations within Ontario, Quebec, and most recently from the Adirondacks in New York, USA. The genetic structure among sampling sites across the entire area revealed a pattern of isolation‐by‐distance (IBD). However, an examination of the distribution of genetic structure (FST/1‐ FST) at different distances showed higher rates of gene flow than predicted under a strict IBD model at small distances (40 km) within clusters and at larger distances up to 100 km among clusters. This pattern of genetic structure suggests increased migration and gene flow among expanding reproductive fronts.

Isolation of peripheral populations of Canada lynx (Lynx canadensis)

“…Carr et al (2007) showed that the St. Lawrence River has not impeded the range expansion of fishers (Pekania (Martes) pennanti (Erxleben, 1777)) from the Adirondack region of New York, USA, into eastern Ontario, Canada. Likewise, Cullingham et al (2009) showed that the St. Lawrence River has allowed gene flow of raccoons (Procyon lotor (L., 1758)), and thus did not stop the spread of the raccoon rabies virus from New York into southeastern Ontario, Canada.…”

Historical and Contemporary DNA Indicate Fisher Decline and Isolation Occurred Prior to the European Settlement of California

“…However, high subdivision is not universal among fisher populations. Populations in southern Ontario, Canada have been found to have weak subdivision and high genetic connectivity attributed to high amounts of gene flow along expansion fronts in a growing population [16], [111].…”

The Sensitivity of Genetic Connectivity Measures to Unsampled and Under-Sampled Sites

“…Previous work on this dataset revealed one genetic cluster ( K  = 1) [30]. The fisher dataset contained 772 individuals sampled at 34 sites across Ontario, northern New York State, USA, and southern Quebec, Canada, between 2000 and 2003 [8], [29], [31]. There were 7–48 individuals sampled per site (average = 21.2, SD = 7.1).…”

“…There were 7–48 individuals sampled per site (average = 21.2, SD = 7.1). The samples were genotyped at 16 microsatellite loci [8]. Previous work with these data suggested 5 genetic clusters ( K  = 5), with 5–11 sites per cluster [8], [29].…”

“…One challenge for landscape geneticists is thus to determine the appropriate spatial sampling scheme for collecting genetic samples. Samples can be collected uniformly across space, with the goal of conducting individual-based analyses [4]–[7], or many samples can be collected from several discrete sites with the goal of conducting site-based analyses [8]–[11]. Where and how many samples are collected may influence the conclusions drawn from landscape genetic analyses.…”