Traits and hidden states: is self-fertilization associated with rates of diversification across mating and sexual systems?

Abstract

Angiosperms, the most diverse group of land plants, possess considerable variation in sexual expression and mating strategy. Reproductive biology is a key determinant of fitness, and may help answer a persistent question in evolutionary biology: why are some areas of the tree of life more species-rich than others? State-dependent speciation-extinction methods (SSEs), which associate traits with patterns of diversification, can be used here. Previously, SSEs have been used within families to investigate the hypothesis that selfing is an evolutionary "dead end." To the best of the authors' knowledge, no study has looked across families, which would increase power to more generally test this hypothesis. Here, we examine the impact of 1) mating system and 2) sexual system on diversification across 18 phylogenetically diverse families. We also discuss how more recent advances in SSE models (i.e., "hidden state" models) influence our interpretation of these patterns and evaluate how the relationship between mating and sexual systems can be leveraged to gain insight into the impact of reproductive biology on evolutionary outcomes. We find that the mating system does not better explain patterns of diversification when compared to null models, but the sexual system often does. We also find family-level heterogeneity in our results, which suggests conclusions drawn from studies on individual families may not be consistent with any broader trend.