Evolutionary impacts of introgressive hybridization in a rapidly evolving group of jumping spiders (F. Salticidae, Habronattus americanus group)

Abstract

Introgressive hybridization can be a powerful force impacting patterns of evolution at multiple taxonomic levels. We aimed to understand how introgression has affected speciation and diversification within a species complex of jumping spiders. The Habronattus americanus subgroup is a recently radiating group of jumping spiders, with species now in contact after hypothesized periods of isolation during glaciation cycles of the Pleistocene. Effects of introgression on genomes and morphology were investigated using phylogenomic and clustering methods using RADseq, ultraconserved elements (UCEs), and morphological data. We characterized 14 unique species/morphs using non-metric multidimensional scaling of morphological data, a majority of which were not recovered as monophyletic in our phylogenomic analyses. Morphological clusters and genetic lineages are highly incongruent, such that geographic region was a greater predictor of phylogenetic relatedness and genomic similarity than species or morph identity. STRUCTURE analyses support this pattern, revealing clusters corresponding to larger geographic regions. A history of rapid radiation in combination with frequent introgression seems to have mostly homogenized the genomes of species in this system, while selective forces maintain distinct male morphologies. GEMMA analyses support this idea by identifying SNPs correlated with distinct male morphologies. Overall, we have uncovered a system at odds with a typical bifurcating evolutionary model, instead supporting one where closely related species evolve together connected through multiple introgression events, creating a reticulate evolutionary history.