Caves as Islands: Population Genetics of Nesticus barri (Araneae: Nesticidae)
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Caves are abundantly found throughout the United States, especially in the southern Appalachian Mountains, and are home to a diverse fauna. This cave fauna, though diverse, often evolves in a convergent manner causing many obligate cave species to have small or absent eyes, to be light colored, and to have long appendages. The spider genus Nesticus is found throughout the southern Appalachian Mountains and Cumberland Plateau and most, though not all, are obligate cave species (troglobites). Nesticus barri are found in approximately sixty caves on the southern Cumberland Plateau in Tennessee and Alabama. This study examined the population genetics of N. barri to see how much gene flow occurs between populations by sequencing the mitochondrial DNA cytochrome oxidase I (COI) gene. We found that N. barri is a monophyletic species with six distinct clades that are largely geographically distinct. No haplotypes were shared between clades, indicating that there is little to no gene flow between populations of this species. This lack of gene flow between caves, and relatively deep divergence between clades, has implications for conservation of these spiders because a loss of any one cave would dramatically decrease the diversity of the population as a whole.
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