Landscape genetics of the small-mouthed salamander (Ambystoma texanum) in a fragmented habitat: Impacts of landscape change on breeding populations in Hardin County, Ohio forests

Habitat loss is the leading cause of species declines and extinctions worldwide. Fragmentation of original habitat into patches often accompanies habitat loss and spatially separates breeding populations across a landscape. Habitat fragmentation poses additional challenges for species by degrading habitat quality, altering population abundance and density, and decreasing gene flow among breeding populations in separate patches. Wetland loss and deforestation in western Ohio has fragmented both breeding and terrestrial habitat for woodland amphibians, where agriculture is now the dominant landuse. This project utilized genetic markers to study the effect of habitat fragmentation on the population structure of a woodland amphibian, the small-mouthed salamander (Ambystoma texanum), in Hardin County, Ohio. This species breeds in vernal pools within forest patches, and has low vagility. It was hypothesized that salamanders were not migrating between forest patches; and that populations in different forest patches would show genetic differentiation and small populations would have decreased genetic diversity. A method was developed to screen for unisexual Ambystoma salamanders, which also reproduce in vernal pools in the study area and whose larvae are difficult to distinguish from A. texanum larvae. For the population genetic analysis, a total of 160 A. texanum from eight breeding populations in five forest patches were genotyped for eight highly polymorphic microsatellite loci. The results indicate that all sampled populations have within-population structure, with the two most isolated populations having the highest inbreeding coefficients. Estimates of historical migration rates reveal that gene flow occurred in the past among sites that today show genetic differentiation. Overall our results suggest that forest fragmentation and wetland loss have reduced the connectivity of breeding populations, which supports numerous studies that implicate landscape change as the main threat to species decline.