Satler, Jordan D., Carstens, Brian C., and Marshal Hedin. 2013. Multilocus species delimitation in a complex of morphologically conserved trapdoor spiders (Mygalomorphae, Antrodiaetidae, Aliatypus). Systematic Biology 62:805-813.
This paper sets out to delimit species within the Aliatypus thompsonii (sensu lato) complex of morphologically conserved trapdoor spiders in southern California. Aliatypus spiders show extremely limited dispersal, especially in females. As a result, these spiders tend to occur in aggregated, geographically isolated populations and exhibit extreme population genetic structure, especially in mtDNA. The authors used rather dense geographic sampling for 1 mtDNA locus but lightened up the sampling for 5 nuclear loci. As a starting point for species delimitation analyses, they hierarchically divided their sampling area into 3 mountain ranges and 16 geologic sub-regions. The 27 multilocus sampling localities had a highly clumped distribution with respect to the 83 mtDNA sampling localities and the 16 sub-regions, but whether or not this matters for species delimitation in this group is an open question.
The meat of the results is Figure 6, which shows a *BEAST tree of individuals from the 27 multilocus sampling localities. Mapped onto this tree are the species delimitations reported by the species validation/discovery methods Structure, bGMYC, Brownie, STEM, BPP, and spedeSTEM. The resulting species delimitations were not at all concordant among methods. This was especially true for Structure, which united the two most basal branches of the *BEAST tree into a single species, and it’s not clear why the Structure results would be so different from the species tree. Despite the discordance among species delimitation methods, the authors went ahead and formally described the two most basal branches of their *BEAST tree as new species. The authors took a conservative approach with respect to describing additional taxonomic diversity. Without a statistical framework for weighing the results of the various methods, deciding how many species to split out is necessarily somewhat subjective. This paper succeeded in illuminating the fascinating spatial complexity of these Aliatypus lineages and in qualitatively comparing several species validation/discovery methods. [UW Phylogenetics Seminar, 11/14/13; Dave Slager]