Hybridization and diversification are positively correlated across vascular plant families

Hybridization has experimental and observational ties to evolutionary processes and outcomes such as adaptation, speciation, and radiation. Although it has been hypothesized that hybridization and diversification are correlated, this idea remains largely untested empirically. Here, we use a hybridization database on 195 plant families, life history information, and a time-calibrated family-level phylogeny to test for phylogenetically-corrected associations between hybridization and diversification rates, while also taking into account life-history traits that may be correlated with both processes. We show that diversification and hybridization are positively correlated using three different methods to estimate diversification rates and two different metrics of hybridization. Moreover, the relationship remains detectable when incorporating the correlations between diversification and two other life history characteristics, perenniality and woodiness. We further provide potential mechanisms for this association under three different scenarios: hybridization may drive diversification, diversification may drive hybridization, or both hybridization and diversification may jointly be driven by other factors. We suggest future studies to disentangle the causal structure.