D3479: Population genetics of Tetraopes texanus

The Texas Longhorn Milkweed Beetle (Cerambycidae Tetraopes texanus) is a uniquely distributed insect that occurs in calcareous grassland habitats. T. texanus is a relatively weak disperser, and relies on a few Asclepias species for feeding and oviposition, thus its distribution and abundance is limited by available habitat and abundance of suitable host-plants. T. texanus primarily occurs in blackland praries of Texas and Oklahoma with some populations on prairie remnants in Arkansas. T. texanus also occurs in the Black Belt prairies of Mississippi and Alabama. This disjunct distribution is likely the result of Pleistocene climatic shifts that reduced and fragmented once extensive prairie habitat. We investigated the population genetics of T. texanus to characterize the genetic structure of a habitat-specialist insect, which could provide insight into how other grassland-adapted insects may respond, genetically, to a reduction in habitat area and connectivity. We collected T. texanus from prairies in Mississippi, Alabama, Oklahoma, and Texas. We extracted DNA with the EZNA extraction kit from Omega-Biotek, and utilized RAD-seq to generate sequence data. We analyzed raw sequence data in STACKS, then calculated pairwise Fst, Heterozygosity, and visualized clustering via principal components analysis. The PCA of sequence data shows strong genetic structuring; Texas/Oklahoma populations form a cluster, while Mississippi/Alabama populations form a separate cluster. Pairwise Fst support isolation by distance as the mechanism driving genetic distance between populations of T. texanus. This implies that grassland-specialist insects with limited dispersal capacity may become genetically isolated as grassland habitats are fragmented.