Vegetative and reproductive variation among unisexual and hermaphroditic individuals of Wurmbea dioica (Colchicaceae)

Abstract

Hermaphroditism may constrain the effects of sex-specific selection on life history and reproductive traits. Wurmbea dioica in south-eastern Australia has populations with male, female and hermaphroditic plants, allowing an intraspecific comparison from which inferences may be made about the nature of evolutionary specialisation for each sexual function. We found that pistillate plants of W. dioica in a population in central Victoria were larger than male plants, but that males produced more and larger flowers. When comparing whole-plant means, males did not differ from hermaphrodites in pollen investment and females did not differ from hermaphrodites in fruit mass. However, when data for individual flowers were analysed with a statistical control for floral size, flowers of hermaphrodites had less investment in both pollen and fruit compared with flowers of the corresponding unisexual plants, implying that an intra-floral allocation trade-off occurs. Investment per flower in pollen had no apparent trade-off with flower number per plant, while fruit investment did show a significant relationship to flower number per plant, but the relationship was in different directions for females and hermaphrodites. Sex-specific selection has apparently favoured differentiation of investment strategies for males and females, while hermaphrodites reveal some morphological compromises that must be made to engage in both sexual functions.