Evaluation of the symmetric effect of antagonists in the floral morphs of the distylic shrub Bouvardia ternifolia: a field study

Abstract

Background: Heterostyly is a genetic polymorphism characterized by a system of sporophyte auto-incompatibility in which the plant populations show two (distyly) or three (tristyly) floral morphs. This reproductive system is known as a promoter of cross-pollination, assuming similar reproductive success between morphs.

Hyphothesis: For this assumption to take place, the pollinators must respond in a similar manner to attraction floral traits in both morphs, maintaining a symmetric flow of pollen. We hypothesize that floral damage by antagonists should correspond to similarities or differences in atractiveness among floral morphs.

Studied species: We tested this hypothesis in the distylous shrub Bouvardia ternifolia (Rubiaceae).

Methods: we evaluated the magnitude of the nectar theft, foliar herbivory, and seed predation by assessing individual plants of both floral morphs throughout their flowering period (June-July 2015) under natural conditions. At the end of the flowering season, we quantified fruit and seed production.

Results: The intensity of the herbivore and nectar thieves in this distylous population is similar between morphs, as well as the size of their floral displays. The number of seeds and fruits produced was also similar between morphs.

Conclusions: Our study showed that selection pressures imposed by antagonists were similar to both floral morphs in the studied population of Bouvardia ternifolia.