Correlations between and habitat predictors of species and genetic diversity in pond-breeding amphibians

Background/Question/Methods

Despite the importance of genetic diversity for populations’ abilities to adapt, conservation resources are often targeted towards protecting species diversity over genetic diversity. However, when neutral processes (extinction and colonization) are responsible for distributions of species across communities, and parallel processes at the genetic level (genetic drift and gene flow) dictate distributions of genetic diversity across populations, species diversity conservation efforts may also benefit the conservation of genetic diversity. To investigate the relationship between and habitat predictors of species and genetic diversity, we performed amphibian surveys at 15 wetlands at Ichauway, a longleaf pine reserve in Baker County, Georgia. We collected 265 dwarf salamander (Eurycea quadridigitata) and 246 leopard frog (Lithobates sphenocephalus) tissue samples from 8 and 9 of these wetlands, respectively. Dwarf salamander and southern leopard frog DNA samples were screened at 12 and 11 microsatellite loci, respectively. We used Pearson correlations to determine the relationship between species and allelic richness. To determine which variables were most closely associated with species and allelic richness, we modeled species richness (SR) within communities and allelic richness (AR) within populations as functions of local (wetland area, hydroperiod, and isolation) and landscape scale land cover variables (forest, agriculture, wetlands, and development) across three spatial scales (0.5, 1.0, and 2.5 km).

Results/Conclusions

Dwarf salamander AR was not correlated with SR (r2=0.103, P=0.439), whereas southern leopard frog AR was negatively correlated with SR (r2=0.5, P=0.033), suggesting that species and/or genetic diversity were not determined by neutral processes. However, single outlier sites for both focal genetic species were driving these linear trends, suggesting the statistical significance of the relationships may differ from the ecological significance. AR of dwarf salamanders was best predicted by the area of wetlands within 2.5km (β=12.07; 95%CI: 4.56-19.59; r2=0.62), which suggests the importance of proximity and abundance of potential source populations to dwarf salamanders. The top model of southern leopard frog AR was the area of agriculture within 2.5km (β=2.14; 95%CI: -0.21-4.49; r2=0.31), however the model was relatively poor at predicting AR, suggesting southern leopard frog population structure may not be closely associated with habitat features at the scale of our study. SR was best predicted by the area of forests within 2.5km (β=14.74; 95%CI: 4.73-24.74; r2=0.39), suggesting non-breeding and dispersal habitat are important for amphibians at Ichauway. These results suggest that a management strategy that protects wetlands and forested habitats would benefit amphibian species and genetic diversity at Ichauway.