Sexual dimorphism and female advantage hypothesis in the gynomonoecious-gynodioecious Dianthus plumarius (Caryophyllaceae)

Abstract

To explain the co-existence and maintenance of females along with hermaphrodite plants, the female-advantage hypothesis has been proposed where females should show greater fecundity compared to their conspecific hermaphrodites. On the other hand, greater attraction would be selected in the hermaphrodites to increase their male function, potentially leading to larger showier flowers, with more rewards. Here, I tested the sexual dimorphism trade-off hypothesis with the gynomonoecious-gynodioecious Dianthus plumarius (Caryophyllaceae), in the gardens of Bariloche (Patagonia, Argentina). I measured in female and hermaphrodite plants: flower size, nectar volume and concentration, flower lifespan, ovule production, seed number, seed set, and seed weight. Additionally, bagging and pollen supplementation experiments were carried out to evaluate pollen limitation, probability of apomixis, if spontaneous autogamy is possible, and to examine the importance of pollen origin. I found that hermaphrodite flowers are more attractive, with larger-sized flowers and higher nectar volume, whereas female flowers compensate with longer lifespan of stigmatic receptivity and more concentrated nectar. Despite ovule number was lower in female flowers, these showed higher seed-set, and produced more and heavier seeds than hermaphrodites under open pollination. No evidence of apomixis was found in females, but spontaneous autogamy may occur in hermaphrodites. Hand-pollination experiments showed first that both flower-types suffered pollen-limitation, but it was higher on hermaphrodite flowers. Finally, despite self-compatibility, pollen origin is important because hand self-pollination decreased seed weight. These findings provide strong evidence in support to the mechanisms and underlying conditions that would allow the co-existence and maintenance of female and hermaphrodite individuals within populations.