Determining the phylogeographic dynamics of the edge relationships between Aphonopelma hentzi (Girard) and its neighbors along the Colorado River Basin (Araneae, Mygalomorphae, Theraphosidae)

Abstract

Theraphosids, commonly known as “tarantulas”, are a group of large, hirsute spiders that have drawn relatively little interest in ecological, behavioral, or evolutionary research from biologists. The lack of research on theraphosids is problematic because of conservation concerns for this group and the need to compile good life history data, and determine taxonomic and phylogenetic relationships. I examined the phylogenetic relationships among populations of tarantulas of the genus Aphonopelma along the Colorado River basin in Texas to construct a framework within which to test ecological, evolutionary, and biogeographical hypotheses in an area of species transition and possible Pleistocene refugia. In order to examine relationships among populations of the A. hentzi tarantulas and populations of neighboring species 890 bp were sequenced from two mitochondrial genes, 16S and ND1, and their corresponding tRNA from 135 individuals. Ecological niche modeling was used to determine potential species distributions, both current and 21,000 ybp during the last glacial maximum of the Pleistocene. Phylogenetic analysis suggests that there may be as many as eight species in the study area, seven south of the Colorado River and one (A. hentzi) to the north. The species found in the study include A. hentzi, A. anax, A. armada, A. moderatum and four potentially undescribed species (based on genetic distances and phylogenetic support). Population expansion analysis shows that the northern clade of A. hentzi (the Colorado River basin and north) split from the southern clade between 20,000-13,000 ybp, agreeing with the biogeographical hypothesis that the Colorado River basin was an area of Pleistocene refugia.