Mapping fitness landscapes to interpret sex allocation in hermaphrodites

Sex-allocation theory predicts sex ratios of dioecious organisms, but it has been poor at explaining sex allocation in hermaphrodites in which the assumed trade-off between male and female functions is often obscure. Here, we apply sex-allocation theory to hermaphrodites by mapping components of seasonal reproductive success onto a fitness landscape defined by potentially independent measures of allocation to male and female functions on orthogonal axes. We find that peaks of reproductive success in a perennial hermaphroditic plant reflect the interactive effect of both male and female allocations on self-fertilization and the effects of inbreeding depression. The rugged landscape corresponds well to the complex pattern of sex allocation observed in natural populations in which individuals produce a mix of male and bisexual flowers and express a type of gender diphasy. Our approach may help to interpret common complexities of sex allocation in hermaphroditic plants and animals.