Temporal floral sex allocation in protogynous Aquilegia yabeana contrasts with protandrous species: Support for the mating environment hypothesis

Abstract

We tested one of the predictions of Brunet and Charlesworth (1995) that relative floral sex allocation will vary temporally with the mating environment and that the form of dichogamy (protandry vs. protogyny) will select for the pattern of variation in male versus female resource allocation. In many hermaphroditic plant species, allocation to female function (ovule number) decreases from early to late flowers within inflorescences as a result of resource limitation or ontogenetic changes. This pattern may obscure the effects of the mating environment and dichogamy on selection for allocation patterns in protandrous species (male allocation increases regardless). By examining a protogynous species the alternative pattern of temporal variation in resource allocation is predicted, namely that allocation to male function should decrease (or female allocation increase) throughout the flowering sequence. This pattern was observed in protogynous Aquilegia yabeana (Ranunculaceae), in which ovule number per flower remained constant whereas pollen number decreased in sequentially blooming flowers. These observations support the temporal sex allocation hypothesis of Brunet and Charlesworth (1995).