Metapopulation genetics of endangered reticulated flatwoods salamanders (Ambystoma bishopi) in a dynamic and fragmented landscape

Abstract

The reticulated flatwoods salamander (Ambystoma bishopi), an endangered species endemic to the longleaf-pine savanna ecosystem of the southeastern U.S., persists in a small number of remnant habitat patches. Breeding ponds and associated populations are threatened by habitat loss, degradation, and fragmentation stemming from fire suppression and land conversion. Understanding influences on population dynamics and genetic diversity will help inform recovery efforts for this and other pond-breeding amphibians. We used 9 microsatellite loci to characterize population structure, migration, and genetic diversity of juvenile (larvae and metamorphs) A. bishopi (n = 607) sampled from thirteen breeding ponds across two breeding seasons. Temporal genetic variation between annual cohorts was minimal compared to spatial variation among locations. The primary genetic subdivision was between two regional groups of breeding ponds (i.e. metapopulations), which were located more than 10 km from each other. Yet even within metapopulations, genetic isolation-by-distance was pronounced, and estimated migration rates among ponds separated by > 400 m were very low. Genetic diversity was positively correlated with the area of suitable breeding habitat in a pond and negatively correlated with distance to other occupied ponds. The effective number of breeders typically was < 30 individuals per year per pond, and all populations showed signs of having been through a severe demographic bottleneck. Small and variable local population sizes suggest the importance of metapopulation dynamics among ponds for maintaining regional persistence and genetic diversity. Such dynamics may be easily disrupted for A. bishopi, so maintaining and restoring connectivity appears crucial for long-term conservation.