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

• Published in: AoB plants Vol. 15; no. 6; p. plad084
• Main Author: Gavini, Sabrina S
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01.12.2023
• Subjects: Studies; geitonogamy; Bumblebees; ovule number; nectar production; dimorphism; inbreeding depression; gynodioecy; rewards; flower size; Dianthus plumarius
• ISSN: 2041-2851; 2041-2851
• DOI: 10.1093/aobpla/plad084

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 decreases seed weight. These findings provide strong evidence in support of the mechanisms and underlying conditions that would allow the co-existence and maintenance of female and hermaphrodite individuals within populations. My findings provide evidence in support of the mechanisms and underlying conditions that would allow the co-existence of female and hermaphrodite plants within populations. The enigma lies in why females are maintained amid competition with hermaphrodites that gain fitness through both female and male functions. First, a higher attraction would be selected in hermaphrodites to increase their male function; certainly, hermaphrodites of Dianthus plumarius showed larger-sized flowers with higher nectar availability. Second, a necessary condition is that females should exhibit a fertility advantage. It is confirmed the existence of this female fertility advantage in D. plumarius . Particularly, female flowers showed extended stigmatic lifespan, and more concentrated nectar, but more importantly, these yielded more and heavier seeds compared to their hermaphrodite counterparts.