Effects of urbanization on genetic diversity, gene flow, and population structure in the ornate box turtle (Terrapene ornata)

Abstract

Large-scale declines in North American box turtle (Terrapene spp.) populations have been attributed to habitat fragmentation as a result of urbanization. We compared microsatellite markers and mitochondrial control region sequences of Ornate Box Turtles (Terrapene ornata) in two populations (a natural and an urban habitat) to test two hypotheses. We hypothesized that urban populations of T. ornata experience genetic bottlenecks due to road mortality and habitat fragmentation, and that roadways represent a barrier to gene flow among turtle populations, resulting in increased fragmentation of gene pools. Both populations shared similar allelic diversity and observed heterozygosity, with eight and seven of twelve microsatellite loci exhibiting heterozygote deficiency in the natural and urban populations, respectively. The number of mitochondrial control region haplotypes in the urban population was nearly four times that of the natural population, although only one haplotype occurred in appreciable frequency in both populations. We did not detect conclusive evidence of a recent genetic bottleneck in the urban population, thereby rejecting our first hypothesis. We detected weak differentiation among populations on opposing sides of a large highway, but did not detect any evidence of population structure, thereby rejecting our second hypothesis. This study indicates that a population of T. ornata with moderate road mortality currently has high genetic diversity, moderate inbreeding, and displays some evidence of genetic differentiation, but no conclusive evidence of recent genetic bottlenecks or unique genetic clustering. We suggest this is primarily due to the species long generation time and is a positive aspect of their life-history.