Characterizing population structure and documenting rapid loss of genetic diversity in Chiricahua Leopard Frogs (Lithobates chiricahuensis) with high throughput microsatellite genotyping

Abstract

The use of molecular markers to assess genetic diversity has become a common component of recovery action plans for threatened and endangered species. In this study, we use an unusually large number of microsatellite markers (N=91) to characterize the genetic variation of Chiricahua Leopard Frogs (Lithobates chiricahuensis) across their range in order to understand their distribution of genetic variation, identify genetic bottlenecks, and measure genetic changes over time in a single, highly-managed population. Populations were best divided into three genetically distinct clusters, with the southeastern Arizona and New Mexico populations forming distinct genetic clusters. While there is moderate genetic variation distributed across the sampled populations, each population on its own shows relatively low allelic diversity. Most populations displayed strong genetic signals of recent genetic bottlenecks or a deficiency of heterozygous genotypes that is typically associated with frequent inbreeding. Populations that have a history of no management through translocations harbored the greatest number of unique alleles and overall allelic richness, especially in a subset of the Mexican populations. Finally, long-term cohort sampling at one specific site (the Southwestern Research Station in Portal, Arizona) allowed us to demonstrate how rapidly genetic diversity can decrease across a matter of years in a population with few founders. This work shows how microsatellite markers can provide important context for conservation agencies, but even a large suite of markers beyond what is typical may not be enough for populations that are extremely bottlenecked and have low levels of standing genetic diversity.