Abstract
A major goal of evolutionary biology is to identify key evolutionary transitions that correspond with shifts in speciation and extinction rates. Here we test the association of transitions in plant mating system with shifts in diversification rates using a novel stochastic character mapping method that identifies the timing and nature of both transitions in trait evolution and diversification rate shifts over evolutionary trees. Utilizing a state-dependent speciation and extinction (SSE) model and a densely sampled fossil-calibrated phylogeny of the plant family Onagraceae, we confirm long standing theory that self-compatible lineages have higher extinction rates and lower net diversification rates compared to self-incompatible lineages. Furthermore, our results provide the first empirical evidence for the "senescing" diversification rates predicted in highly selfing lineages: our mapped character histories show that the loss of self-incompatibility is followed by a short-term spike in speciation rates, which declines after a time lag of several million years resulting in negative net diversification. Lineages that have long been self-compatible such as Fuchsia and Clarkia are in a previously unrecognized and ongoing evolutionary decline.
