A comparative study of the feral horses of Shackleford Banks and Assateague Island [abstract]

Abstract

Feral horses (Equus caballus) can be found today in isolated barrier island populations along the eastern coast of the United States. Assateague Island stretches for 37 miles along the coasts of Maryland and Virginia and is home to about 160 horses. Shackleford Banks, North Carolina is only about nine miles long, and supports an average of 130 horses. Legend persists that these horses washed ashore from Spanish colonial vessels that had shipwrecked nearby, so they may have some common ancestry. They are managed by the National Park Service for the enjoyment of the public, and also serve as a natural laboratory for developing techniques useful in managing large mammal populations. Natural disasters and diseases can pose a threat to the survivorship of these equids. How to augment decimated populations is a management question of immediate concern. We are performing a comparative study of the two populations to assess their genetic and ecological exchangeability. Dr. Eggert has previously assessed the genetic status of the Assateague Island populations; these data have been used for comparison. I have collected fecal samples from 32 horses on Shackleford Banks, and extracted DNA using the Guanadine Thiocyanate/Silica method of Eggert et al. (2005). We used six microsatellite loci to investigate nuclear genetic variability. Allele sizes were determined in an automated sequencer, and the results were scored using GeneMarker. The two populations exhibit significant differentiation at all six loci. This might suggest that the two are not genetically exchangeable. However, this large genetic distance may simply be a result of the heightened genetic drift common in small populations, and therefore it is important to test for ecological differentiation.