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

in Amphibia-Reptilia
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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.

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

in Amphibia-Reptilia



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  • View in gallery

    (a) Sampling localities of T. ornata from a natural area (Matador Wildlife Management Area; Cottle County, Texas; grey with black outline) and an urbanized area (Cooke and Grayson Counties, Texas; white with black outline). (b) Map of Cooke and Grayson Counties, Texas (thick dark grey lines indicate county boundaries) with the two sampling boundaries (Interstate-35 [I35] and Highway 75 [HWY75]) and three roads with high traffic volumes (Highway 82 [HWY82], Highway 377 [HWY377], and Highway 56 [HWY56]) indicated in black.

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    Number of alleles estimated at the end of each of the ten simulations. Filled circles are allele numbers from simulations with total starting population sizes of 500 individuals. Empty circles are allele numbers from simulations with total starting population sizes of 1000 individuals. Bars represent one standard error.

  • View in gallery

    An unrooted tree showing the relationships among the mitochondrial control region haplotypes from the natural and urban population. The number of times each haplotype was observed in the natural population and two potential urban populations (north and south of Highway 82) is indicated at the end of each branch with each population separated by an underscore.

  • View in gallery

    Mean q-values of 10 iterations for all 80 individuals sampled when K=2. Turtles sampled from the natural population are indicated with dark grey bars, turtles sampled north of Highway 82 have medium grey bars, and turtles sampled south of Highway 82 have light grey bars. A high q-value is indicative of a turtle with high urban ancestry whereas a low q-value is indicative of a turtle with high natural ancestry. Standard error of the 10 iterations was too small to be displayed on the graph (SE < 0.001 for most individuals).


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