Authors
  • Howes, Briar J.
  • Brown, Joseph A.
  • Gibbs, H. Lisle
  • Herman, Tom
  • Mockford, Stephen
  • Prior, Kent
  • Weatherhead, Patrick J.

Summary

The estimation and maintenance of connectivity among local populations is an important conservation goal for many species at risk. We used Bayesian statistics and coalescent theory to estimate short- and long-term directional gene flow among subpopulations for two reptiles that occur in Canada as peripheral populations that are geographically disjunct from the core of their respective species’ ranges: the black ratsnake and the Blanding’s turtle. Estimates of directional gene flow were used to examine population connectivity and potential genetic source-sink dynamics. For both species, our estimates of directional short- and long-term gene flow were consistently lower than estimates inferred previously from F ST measures. Short- and long-term gene flow estimates were discordant in both species, suggesting that population dynamics have varied temporally in both species. These estimates of directional gene flow were used to identify specific subpopulations in both species that may be of high conservation value because they are net exporters of individuals to other subpopulations. Overall, our results show that the use of more sophisticated methods to evaluate population genetic data can provide valuable information for the conservation of species at risk, including bidirectional estimates of subpopulation connectivity that rely on fewer assumptions than more traditional analyses. Such information can be used by conservation practitioners to better understand the geographic scope required to maintain a functional metapopulation, determine which habitat corridors within a working landscape may be most important to maintain connectivity among subpopulations, and to prioritize subpopulations with respect to their potential to act as genetic sources within the metapopulation.

Methodology

Sampling

Collection of microsatellite data for ratsnakes used in this study is described in Lougheed et al. (1999). We refer to a local sampling unit as a subpopulation, and the collective group of sampling units as a metapopulation. Sampled subpopulations within the metapopulation of eastern Ontario were Charleston Lake Provincial Park (CLPP), LaRue Mills (LRM), Murphy’s Point Provincial Park (MPPP), St. Lawrence Islands National Park (SLINP), and Queen’s University Biological Station (QUBS) (Fig. 1, Table 1).

Collection of microsatellite data for Blanding’s turtles used in this study is described in Mockford et al. (2005). Sampled subpopulations within the metapopulation of Nova Scotia were Kejimkujik National Park (KNP), McGowan Lake (ML), and Pleasant River (PR) (Fig. 2, Table 1).

Genetic structure

For both species, we tested for linkage disequilibrium between all pairs of loci and for departures from Hardy–Weinberg expectations using a Markov chain approximation of an exact test as implemented in GENEPOP web version 3.4 (Raymond and Rousset 1995).

We first examined genetic structure in both metapopulations using the program BAPS Version 3.2 (Corander et al. 2003) and the approach in which groups of individuals are clustered. We also used the program GENECLASS2, Version 2.0 (Piry et al. 2004), to examine genetic structure in both metapopulations based on assignment tests. Assignment probabilities of individuals were calculated using a Bayesian procedure (Rannala and Mountain 1997) and Monte Carlo re-sampling techniques using 100,000 simulated individuals and a threshold of 0.01.

Location