BackgroundThe primary objective of this study is to reconstruct the phylogeny of the hentzi species group and sister species in the North American tarantula genus, Aphonopelma, using a set of mitochondrial DNA markers that include the animal “barcoding gene”. An mtDNA genealogy is used to consider questions regarding species boundary delimitation and to evaluate timing of divergence to infer historical biogeographic events that played a role in shaping the present-day diversity and distribution. We aimed to identify potential refugial locations, directionality of range expansion, and test whether A. hentzi post-glacial expansion fit a predicted time frame.Methods and FindingsA Bayesian phylogenetic approach was used to analyze a 2051 base pair (bp) mtDNA data matrix comprising aligned fragments of the gene regions CO1 (1165 bp) and ND1-16S (886 bp). Multiple species delimitation techniques (DNA tree-based methods, a “barcode gap” using percent of pairwise sequence divergence (uncorrected p-distances), and the GMYC method) consistently recognized a number of divergent and genealogically exclusive groups.ConclusionsThe use of numerous species delimitation methods, in concert, provide an effective approach to dissecting species boundaries in this spider group; as well they seem to provide strong evidence for a number of nominal, previously undiscovered, and cryptic species. Our data also indicate that Pleistocene habitat fragmentation and subsequent range expansion events may have shaped contemporary phylogeographic patterns of Aphonopelma diversity in the southwestern United States, particularly for the A. hentzi species group. These findings indicate that future species delimitation approaches need to be analyzed in context of a number of factors, such as the sampling distribution, loci used, biogeographic history, breadth of morphological variation, ecological factors, and behavioral data, to make truly integrative decisions about what constitutes an evolutionary lineage recognized as a “species”.

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Coexisting species from the same ecological guild often exhibit different adaptations to discontinuous, abiotic environmental factors. In the laboratory, we compared tolerance to thermal and desiccation stress among three sympatric wolf spiders (Pirata sedentarius Montgomery, 1904, Pardosa lapidicina Emerton, 1885, and Pardosa fuscula Thorell, 1875). In the field, we examined spatial structure across a microhabitat (moisture) gradient in a streamside cobble habitat where these three species are abundant. Female P. sedentarius succumbed more quickly to desiccation stress than females of either Pardosa species. In the absence of thermal stress, desiccation tolerance was high for both Pardosa species. However, P. fuscula appears to be more resistant to combined thermal and desiccation stress than P. lapidicina. These findings correspond with the results of the field survey; the distribution of P. sedentarius was the most restricted (by proximity to the shoreline) among the three species. Contingency analyses also revealed greater relative abundance of P. fuscula than P. lapidicina farther away from the creek. Further examination of spatial structure suggests that neither of these two species was restricted by proximity to the shoreline within the sampling grid.