Dispersal abilities and genetic population structure of insular and mainland Oryzomys palustris and Peromyscus leucopus

Abstract

A comparative hierarchical approach was used to examine allozymic variability within and among nine populations of Oryzomys palustris (marsh rice rat) and seven populations of Peromyscus leucopus (white-footed mouse) from the Virginia barrier islands and southern Delmarva Peninsula. O. palustris is an effective disperser over water and is present on 21 of 24 islands. In contrast, P. leucopus is a less effective disperser over water and occurs on only four of 24 islands. Of 31 loci, four were variable in O. palustris; six were variable in P. leucopus. The nine populations of O. palustris had an average heterozygosity of 2.4% with 6.7% polymorphic loci. For seven populations of P. leucopus, the average heterozygosity was 3.6% with 12.3% polymorphic loci. Both species had lower levels of variation among mainland populations than among island populations. Populations of P. leucopus exhibited considerable genetic differentiation (FST = 0.180) and lower levels of gene flow (Nm = 1.14) among populations, whereas O. palustris had moderate levels of differentiation (FST = 0.135) and higher levels of gene flow (Nm = 1.60) among populations. Mantel tests indicated a significant relationship between genetic distance and geographic distance in Oryzomys but not in Peromyscus.