Temporal genetic and demographic monitoring of pond-breeding amphibians in three contrasting population systems

Abstract

Quantifying the relationship between demographic patterns and genetic diversity are important in predicting temporal population genetic changes. To make predictions there must be an understanding of the relationship between census size, the effective number of breeders (Nb) and effective population size (Ne). We evaluate the temporal genetic variation between three populations of Ambystoma salamanders, and compare genetic and demographic estimates of Nb and Ne. We sampled two wetlands, RB and GB for A. opacum and sampled A. talpoideum at RB, over a 20-year period. Ambystoma opacum colonized the RB wetland in 1980 and the population has steadily expanded as A. talpoideum has declined towards local extinction; the GB population of A. opacum has remained relatively large and stable over this same time period. Genetic variation at 10 microsatellites remained stable at each population over the sampled time frame, and did not reflect changes in population size. Genetic estimates of Nb also did not reflect demographic trends, and were lower than demographic estimates of Nb. Genetic methods of determining Ne gave similar estimates to demographic methods. Our findings indicate that sample sizes and number of markers typically used in genetic studies do not provide enough precision to monitor population size changes in amphibians, which likely violate many of the assumptions of Nb and Ne estimation models. These findings should be considered when using Ne in conservation and management assessments of amphibian populations.