VARIATION IN LIFETIME MALE FITNESS IN IPOMOPSIS-AGGREGATA - TESTS OF SEX ALLOCATION THEORY

Sex allocation theory assumes that a shift in allocation of resources to male function both increases male fitness and decreases female fitn ess. Moreover, the shapes of these fitness gain functions determine wh ether hermaphroditism or another breeding system is evolutionarily sta ble. In this article, I first outline information needed to measure th ese functions in flowering plants. I then use paternity analysis to de scribe the shapes of the fitness gain functions in natural populations of the hermaphroditic herb Ipomopsis aggregata. I also explore the re lationships of male fitness (number of seeds sired) and female fitness (number of seeds produced) to the number of flowers produced by a pla nt. Plants with greater investment of biomass in the androecium, compa red to the gynoecium and seeds, showed increased success at siring see ds, as assumed by the models. That sex allocation trait, however, expl ained only 9% of the variance in estimates of male fitness. The shapes of the fitness gain functions were consistent with theoretical expect ations for a hermaphroditic plant, but the model predicted a more fema le-biased evolutionarily stable strategy (ESS) allocation than was obs erved. These results lend only partial support to the classical sex al location model.