Effects of habitat fragmentation and water quality on wood frog population genetic structure in vernal pools

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Gabrielsen, Charlotte
Agriculture; Wildlife Conservation; Wildlife Management
thesis / dissertation description
Habitat fragmentation associated with suburbanization can have negative consequences on population persistence through the reduction of dispersal and concomitant gene flow. Using nine polymorphic microsatellite loci, I assessed the effects of forest fragmentation and water quality on the genetic structure of a vernal pool-breeding amphibian, the wood frog ( Lithobates sylvaticus), across 20 ponds in an unfragmented, forested landscape and 45 ponds in a fragmented landscape. Analyses were performed at the broad-scale of the study area and at a fine-scale, with spatially independent clusters of ponds selected within each landscape. Bayesian clustering approaches and AMOVA identified little population structure at the scale of the study area. At the fine-scale analysis, however, BARRIER and maps of genetic divergence identified barriers associated primarily with roads and suburban development in the fragmented landscape, and with large bodies of water and elevation in the unfragmented landscape. Tests of isolation by distance and Mantel tests of road effects and genetic differentiation (FST) were significant in only one of the three clusters in the fragmented landscape. Spatial autocorrelation and calculation of mean parent-offspring dispersal distances indicated restricted dispersal in a different cluster of pools in the fragmented landscape. Lastly, using the program GESTE, I tested the potential effects of water quality and hydroperiod on the observed genetic patterns and found that pH had a significant effect on structuring in the fragmented landscape, with higher pH resulting in increased genetic differentiation. The results of this study indicate that wood frog populations are well connected across the landscape of southeastern New Hampshire. However, I detected fine-scale population structuring associated with roads and other fragmenting features of suburbanization. Though inconsistent over clusters, this suggests that increased fragmentation might negatively impact wood frog populations in the future.