The Effects of Habitat Fragmentation on the Yazoo Darter, a Range-Restricted Endemic Fish

The Yazoo darter, Etheostoma raneyi (Percidae, subgenus Ulocentra), is a small benthic insectivore endemic to the headwater streams of two river systems in the upper Yazoo River basin in north-central Mississippi.  The species lives < 3 years, has a female biased sex ratio, and has relatively low fecundity.  Extensive anthropogenic habitat alteration has created ostensible barriers to dispersal in the form of numerous impoundments, road crossings, and channelized stream reaches.  However, this headwater fish species possibly existed in semi-isolated populations before European settlement.  Related work revealed a relatively high level of population structure within and among watersheds across the range of the species, and excess heterozygosity relative to Hardy-Weinberg expectations indicated that relatively recent population declines may have occurred.  Here, our goal was to quantify population declines, estimate effective population sizes (Ne) and determine if detectable levels of migration have occurred both recently and historically among populations using data obtained from microsatellite markers.  Using two different approaches, we found evidence for population bottlenecks across the range of the species and we found small contemporary effective population sizes across all genetically distinct populations using two different approaches.  We also found that there have been recent and severe declines in contemporary migration rates as compared to historical rates of migration.  Our findings suggest that anthropogenic habitat alteration has resulted in population fragmentation and isolation and a general trend of decline in effective population size to dangerously low levels.