Phylogenetic exploration of mating system evolution in the eastern North American leiobunine harvestmen (Opiliones: Sclerosomatidae)

Abstract

Understanding the basis for the vast diversity in reproductive structures found within the animal kingdom is a perennial issue in evolutionary biology. Meanwhile, taxonomists have long capitalized on the substantial genital diversity in the eastern North American leiobunine harvestmen for identifying and delimiting species, but no attempts have been made to explore the functional or evolutionary significance of this variety. Past discussion of the evolution of reproductive heterogeneity attributes genitalic diversification to female preferences, although recent work has also emphasized the (potentially competing) importance of intersexual conflict leading to sexually antagonistic coevolution. Here I test the overarching support for diversification of reproductive structures in leiobunine harvestmen via female choice and sexual conflict mechanisms of sexual selection. My dissertation work consisted of 1) reconstructing the phylogeny of eastern North American leiobunine harvestmen using molecular characters, 2) mapping and simulating relevant discrete morphological features, and 3), using biomechanical and kinetic reproductive data to test whether the direction of evolutionary change in reproductive characters within and between sexes is consistent with increasing sexual antagonism through evolutionary time via a comparative approach. I found support for the monophyly of the eastern North American leiobunine harvestmen, as well as evidence for an evolutionary transition from enticement-based mating to conflict-based systems. My novel uses of phylogenetic comparative methods to quantify mating systems demonstrate that leiobunine species form a continuum of reproductive diversity ranging from specialization in female enticement to precopulatory antagonistic contexts, with correlations between male and female discrete and continuous traits, suggesting long-term sexual coevolution has occurred. I conclude that mating system evolution has occurred in the leiobunine harvestmen, with sexual selection as its ultimate driver, and I offer hypotheses as to the origins of sexual conflict in these temperate lineages.