9 - Size-Dependent Allocation to Male and Female Reproduction

Abstract

This chapter examines size-dependent allocation to male and female reproduction in case of hermaphrodite monocarpic plants. In contrast to the animal kingdom where individuals of most species have separate sexes, in most plant species, individuals combine both sexes usually even within the same flower, and 72% of all plant species are hermaphrodite. With respect to sex allocation, hermaphrodites are considered to be invariant in their behavior, because all their flowers have functional pollen and ovules. Hermaphrodite individuals are not necessarily equally effective male and female parents. Some hermaphrodite individuals do not set seed at all. The results obtained in the study show that sex allocation in plants is size dependent. Size-dependent sex allocation patterns are different for groups of plants with different pollination systems. These patterns seem to be adaptive, but much more knowledge is needed about the relationship between plant size and fitness. The study also indicates that there is need for a better understanding of the physiological regulation of flower, pollen, and seed production and abortion of ovules and seeds.