Microtus pennsylvanicus (Rodentia: Muridae) in Florida: A Pleistocene relict in a coastal saltmarsh

Abstract

Microtus pennsylvanicus exists as a disjunct relictual population in a tidal salt marsh located on Waccasassa Bay on the Florida Gulf coast. This form, described as a new subspecies, inhabits Distichlis flats and other areas of low vegetation in the salt marsh, while Oryzomys is more common in areas of Juncus. The saltmarsh vole was less abundant than Oryzomys during the study period. In comparison with other forms of Microtus pennsylvanicus, the saltmarsh vole is larger in body size, darker in coloration, and has a larger hind foot. The current distribution of the new subspecies of Microtus appears to be relictual from a more widespread range in the Gulf Coastal Plain during the last 10,000 years. The range of the vole presumably was restricted by changes in vegetation and rising sea levels during the last 8000 years. The vole is in a grassland habitat isolated by unsuitable forest habitat and is 500 km south of the nearest population of M. p. pennsyluanicus in Georgia. Analysis of blood proteins indicates a lack of genetic diversity, a condition that prevails in other insular populations of Microtus pennsylvanicia. The saltmarsh vole survives in low numbers under very harsh ecological conditions and is vulnerable to extirpation by natural disasters associated with wind and water.