Floral intra-individual variation differs between morphs and is linked to pollen deposition in self-incompatible distylous plants.

Abstract

Flowers are expected to exhibit lower trait variability than vegetative traits, thereby enhancing precise pollination and reproductive success, especially in self-incompatible species that rely on cross-pollination. This is particularly important in distylous plants, which have two co-dependent flower morphs with reciprocal positioning of sexual structures (L- and S-morph). However, the influence of intra-individual floral variation on the reproductive process has often been neglected, even though this variation underlies selection for precise floral adjustment. This study investigated the intra-individual variation in floral traits across different morphs and populations of distylous plants with contrasting pollinator guilds (bees and hummingbirds), focusing on the implications of this variation for reproductive success and floral resource features. We showed intra-individual variation differences between morphs and populations in stigma length and stigma height, which may reflect distinct pollination pressure across populations. Contrastingly, the similar levels of variation are maintained across morphs, potentially facilitating effective pollen transfer within these self-incompatible distylous populations. Intra-individual variation in corolla length was positively associated with total pollen deposition, which was also morph-dependent (greater in L-morph flowers in the bee-pollinated population). However, intra-individual variation did not affect fruit set. Our results provide a novel perspective on the effect of intra-individual variation in the reproductive process of distylous plants, indicating that such variation might serve as a strategy to occupy a greater positional range accessed by distinct pollinators, which would increase the chances of cross-pollen deposition among flowers within individuals.