Phylogenomics of endangered troglobiotic rove beetles (Coleoptera: Staphylinidae: Pselaphinae) from central Texas karst regions

The karst habitats of central Texas, USA, are home to an array of endemic subterranean-obligate (troglobiotic) invertebrates. This includes several species of rove beetles (Coleoptera: Staphylinidae: Pselaphinae). Here we developed a molecular dataset using sequence capture of Ultra-Conserved Elements (UCEs) from the Coleoptera-UCE-1.1 K v1 baits kit. These data were used to assess species relationships and patterns of diversification in this group, specifically among species within the genera Batrisodes Reitter 1882 and Texamaurops Barr and Steeves 1963; with a specific focus on the relationships of the federally listed as endangered B. texanus Chandler 1992 and B.cryptotexanus Chandler and Reddell 2001. Our final datasets consisted of 69 individuals (two genera, Batrisodes [five species] and Texamaurops [one species], from 34 localities), and a molecular dataset of 658,560 aligned base pairs across 672 UCE loci. Concatenated and species-tree phylogenetic analyses resolved all troglobiotic taxa as a monophyletic group. Within the Travis and Williamson County troglobionts, we recovered four well-supported clades that generally follow hypothesized geologic barriers to dispersal formalized as karst fauna regions (KFRs). A northward pattern of diversification was observed among these groups: (A) Texamaurops reddelli Barr and Steeves 1963 (Jollyville Plateau KFR); (B) Batrisodes reyesi Chandler 1997 (West Cedar Park and Post Oak Ridge KFRs); (C) B. reyesi (McNeil-Round Rock KFR); (D) B. cryptotexanus + B. texanus (Georgetown and North Williamson KFRs). The morphologically defined Batrisodes texanus and B. cryptotexanus were not reciprocally monophyletic, nor clustered into two unique groups in clustering analyses of single nucleotide polymorphisms (SNPs). Rather, we found support for five major subclades and five to seven genetic clusters. These results suggest that diversification and subsequent isolation of clades may have occurred with the progressive availability of karst habitats over time in the North Williamson and Georgetown KFRs resulting from the interactions of faulting, geologic structure, and drainage basin evolution. Comparison with recent U.S. Fish and Wildlife Service cave habitat resiliency assessments indicated that four genetic clusters occur within at least partially resilient habitat, whereas three are confined to caves with low or impaired resiliency. Integrating genetic results presented here along with results of other molecular studies of co-occurring troglobiotic invertebrates supports considering additional geological substructure within the North Williamson KFR in conservation efforts for these rare and unique lineages and systems.