Correlated evolution of dichogamy and self-incompatibility: A phylogenetic perspective

Historically, dichogamy, the temporal separation of male and female function in flowering plants, has been interpreted as a mechanism for avoiding inbreeding. However, a comparative survey found that many dichogamous species are self-incompatible ( SI), indicating dichogamy evolved for other reasons. Here we reexamined the association between dichogamy and SI in a phylogenetic framework and tested the hypothesis that dichogamy evolved to reduce interference between male and female function. Using paired comparison and maximum likelihood correlation analyses, we found that protandry ( male function first) is positively correlated with the presence of SI and protogyny ( female function first) with self-compatibility (SC). In addition, estimates of transition-rate parameters indicated strong selection for the evolution of SC in protogynous taxa and a constraint against transitions from protandry to protogyny in SC taxa. We interpret these results as support for protandry evolving to reduce interference and protogyny to reduce inbreeding.