Sex-specific differences in floral display and resource allocation in Australian alpine dioecious Aciphylla glacialis (Apiaceae)

Abstract

In one of the few dioecious species in the Australian alpine region, Aciphylla glacialis (F.Muell.) Benth. (Apiaceae) flowering and resource allocation patterns were found to differ between males and females, potentially a response to sex-specific selection under the limited conditions for growth and reproduction imposed by the alpine environment. Sex ratios were male biased with approximately 1.49 males to each female in each of five populations of A. glacialis. Male plants had larger floral displays than female plants, producing four times as many flowers per inflorescence and an average of 3.5 inflorescences per plant, compared to 2.9 inflorescences for females. Male and female plants commenced flowering within a few days of each other (average 18 January for males, 19 January for females) but female plants completed flowering earlier, finishing at the end of January, while males were still flowering well into February. Male and female plants did not differ in size as estimated by the number of stems per plant, nor in the proportion of resources allocated to reproduction compared with above ground vegetative structures. However, they did differ in the way resources were allocated to vegetative and floral structures, particularly among larger plants. Large female plants produced heavier stems and infloresences than males. Heavier inflorescences in females may be associated with the need for greater structural support for inflorescences when fruiting, while the increased dry weight of stems may reflect differences in the ways in which the sexes match growth and resource demands for flowering.