Comparative population genomic diversity and differentiation in trapdoor spiders and relatives (Araneae, Mygalomorphae)

Although patterns of population genomic variation are well-studied in animals, there remains room for studies that focus on non-model taxa with unique biologies. Here we characterize and attempt to explain such patterns in mygalomorph spiders, which are generally sedentary, often occur as spatially clustered demes, and show remarkable longevity. Genome-wide SNP data was collected for 500 individuals across a phylogenetically representative sample of taxa. We inferred genetic populations within focal taxa using a phylogenetically-informed clustering approach, and characterized patterns of diversity and differentiation, within- and among these genetic populations, respectively. Using phylogenetic comparative methods we asked whether geographic range sizes and ecomorphological variables (behavioral niche and body size) significantly explain patterns of diversity and differentiation. Specifically, we predicted higher genetic diversity in genetic populations with larger geographic ranges, and in small-bodied taxa. We also predicted greater genetic differentiation in small-bodied taxa, and in burrowing taxa. We recovered several significant predictors of genetic diversity, but not genetic differentiation. However, we found generally high differentiation across genetic populations for all focal taxa, and a consistent signal for isolation by distance irrespective of behavioral niche or body size. We hypothesize that high population genetic structuring, likely reflecting combined dispersal limitation and microhabitat specificity, is a shared trait for all mygalomorphs. Few studies have found ubiquitous genetic structuring for an entire ancient and species-rich animal clade.