Morph-specific patterns of sex organ positions in species with style length polymorphism

Abstract

In style length polymorphism, morph-specific sequence of encountering male and female sex organs within a flower by pollinators can cause differences in the need to avoid self-pollination and encourage inter-morph pollination. We asked if this difference can lead to disparity in stigma-anther separation (herkogamy) between morphs and spatial match between sex organs of complementary morphs (reciprocity). Further, we tested if herkogamy, and hence the level of selfing, is fairly constant among individuals of a population. Additionally, we examined the relationship between herkogamy and reciprocity among individuals of a population to understand functional interactions between these two morphological traits. Using data on sex organ heights for >200 heterostylous species from the literature, we observed that the short-styled morph had higher herkogamy as compared to the long-styled morph indicating a higher need to avoid selfing. Reciprocity did not show a consistent difference between the upper and lower sex organs implying a strong influence of local ecological factors. In most populations, allometric relationships suggested that herkogamy and hence the level of selfing remains constant. Finally, we observed that herkogamy and reciprocity can be related among individuals of a population, sometimes indicating a potential trade-off between avoidance of self-pollination and facilitation of inter-morph pollination.