BioProject

Animal body size has important evolutionary implications for physiology, sexual selection, and speciation. More...

Animal body size has important evolutionary implications for physiology, sexual selection, and speciation. The wolf spider genus Schizocosa has developed as a model for studies on courtship behavior, with visual and vibratory signals receiving considerable attention; however, body size has not been carefully evaluated in Schizocosa. Although many species of Schizocosa can be distinguished from their close relatives by differences in genitalic structures, male ornamentation, and behavior, some Schizocosa species are morphologically similar, making species delimitation, diagnosis, and subsequent identification difficult. In general, evaluation of species boundaries using genetic data across the genus Schizocosa is limited. The ostensibly similar species S. maxima and S. mccooki are separated predominantly on the basis of size differences, with S. maxima being the larger of the two. Here, we evaluate the evolution of size in these two Schizocosa species distributed in western North America, where gigantism of S. maxima is hypothesized to occur, particularly in California populations. We sampled sub-genomic data (RADseq) and inferred the phylogeny of S. mccooki, S. maxima, and their relatives using concatenated and coalescent-based approaches. We also apply a variational autoencoder machine learning approach to visualize population structuring within the geographically widespread S. mccooki and then evaluate size within the context of a comparative phylogenetic framework to test the evolutionary hypothesis related to genetic clustering of populations and gigantism. Our data shows that S. mccooki populations are not genealogically exclusive with respect to S. maxima, which are recovered as nested within a western clade of S. mccooki. Likewise, S. maxima individuals are not recovered as a single lineage and do not form an isolated genetic cluster, suggesting that the observed differences in size cannot be used to accurately delimit/diagnose species. The underlying cause of gigantism in S. maxima remains unexplained but provides a fertile avenue for studies on size variation and its relationship to speciation. Less...