Reevaluation of species boundaries in coastal dune trapdoor spider Aptostichus simus

Mygalomorph spiders are often characterized by morphological homogeneity and cryptic diversity, which has historically led to underestimation of species diversity between genetically divergent groups. It is now generally acknowledged that the application of traditional taxonomic constructs and strict morphological species delimitation may mislead assessments of species diversity in groups with genetically divergent lineages, thus more integrative approaches when delimiting these morphologically homogenous species is necessary. The trapdoor spider species Aptostichus simus is a California coastal dune endemic with little morphological variation, but substantial genetic structuring. Previous assessment of species boundaries was limited to a single mitochondrial locus and failed to draw any firm conclusions of species boundaries. In this study, we used a combination of a larger sample size of morphological data and modern molecular methods (i.e., 10X low coverage genome scans and ultraconserved element data) to test species hypotheses of A. simus. We tested whether A. simus comprises multiple cryptic species based on the cohesion species concept. This concept is ideal for taxa with high population structuring because it considers ecological and genetic exchangeability in addition to genetic diversity. We analyzed morphological cohesiveness between populations using principal component analyses and analysis of variance, with subsequent examination of divergence at the genomic level through identification of SNPs. The evaluation of genomic data in these dispersal limited, non-model organisms will allow us to gain a greater understanding of the genetic variation between highly structured populations and across the landscape.