Genetic diversity and population structure in the Barrens Topminnow (Fundulus julisia): implications for conservation and management of a critically endangered species

Abstract

The Barrens Topminnow (Fundulus julisia) has undergone a rapid and dramatic decline. In the 1980s, at least twenty localities with Barrens Topminnows were known to exist in the Barrens Plateau region of middle Tennessee; currently only three areas with natural (not stocked) populations remain. The long-term survival of the Barrens Topminnow will depend entirely on effective management and conservation efforts. Captive propagation and stocking of captive-reared juveniles to suitable habitats have successfully established a handful of self-sustaining populations. However, very little is known about the genetic composition of source and introduced populations including levels of genetic diversity and structuring of genetic variation. Here we use both mitochondrial sequence data and genotypes from 14 microsatellite loci to examine patterns of genetic variation among ten sites, including all sites with natural populations and a subset of sites with introduced (stocked) populations of this species. Mitochondrial sequence analysis reveals extremely low levels of variation within populations and fixed differences between drainages. Microsatellite genotype data shows higher levels of genetic variability and a molecular signature consistent with a recent history of population bottlenecks. Measures of genetic diversity at microsatellite loci including allelic richness are similar within source and introduced populations. Bayesian assignment tests and analysis of molecular variation (AMOVA) support two distinct populations, consistent with drainage boundaries. Results from AMOVA analysis also suggest low levels of genetic connectivity between isolated populations within the same drainage. Here we propose two distinct evolutionary significant units (ESUs) and two management units that reflect this population substructure and warrant consideration in future management efforts.