Abstract
The northeastern United States has experienced dramatic alteration to its landscape since the time of European settlement. This alteration has had major impacts on the distribution and abundance of wildlife populations, but the legacy of this landscape change remains largely unexplored for most species of freshwater turtles. We used microsatellite markers to characterize and compare the population genetic structure and diversity between an abundant generalist, the eastern painted turtle (Chrysemys p. picta), and the rare, more specialized, spotted turtle (Clemmys guttata) in Rhode Island, USA. We predicted that because spotted turtles have disproportionately experienced the detrimental effects of habitat loss and fragmentation associated with landscape change, that these effects would manifest in the form of higher inbreeding, less diversity, and greater population genetic structure compared to eastern painted turtles. As expected, eastern painted turtles exhibited little population genetic structure, showed no evidence of inbreeding, and little differentiation among sampling sites. For spotted turtles, however, results were consistent with certain predictions and inconsistent with others. We found evidence of modest inbreeding, as well as tentative evidence of recent population declines. However, genetic diversity and differentiation among sites were comparable between species. As our results do not suggest any major signals of genetic degradation in spotted turtles, the southern region of Rhode Island may serve as a regional conservation reserve network, where the maintenance of population viability and connectivity should be prioritized.
Highlights
Rhode Island, a small state in the northeastern United States, has experienced intensive and large-scale landscape alteration in the last several centuries
To test for the signature of heterozygosity excess, we considered results from both a two-tailed sign test [66] and a one-tailed Wilcoxon signed-rank test using the two-phase mutation model (TPM), with 10,000 iterations used to generate a distribution of expected equilibrium heterozygosity
The vast majority of genetic variance occurred within sites for both species (AMOVA: painted turtle = 96.5%; spotted turtle = 97.9%), with the remaining variance partitioned among sites, and we found no evidence for isolation by distance in painted turtles (r = 0.097, p = 0.128, 21 sites) or spotted turtles (r = −0.454, p = 0.926, 5 sites)
Summary
Rhode Island, a small state in the northeastern United States, has experienced intensive and large-scale landscape alteration in the last several centuries. Drainage, filling, damming, and channelization occurred for centuries without regulation, resulting in the loss of an estimated 37% of the wetlands in Rhode Island between 1780 and 1980 [2,3]. These human activities have had major impacts on the distribution, abundance, and connectivity of populations of wildlife throughout the state and region, but for most species the legacy of this change remains largely anecdotal or completely unexplored.
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