Pollen limitation influences the divergences in mating system and floral traits between two sympatric Halenia species

Abstract

Abstract The mating systems and floral traits often among relatives of hermaphroditic plants can exhibit considerable diversity. This diversity can be influenced by the evolution of selfing and associated floral traits as a form of reproductive assurance when pollen limitation results from insufficient pollinator availability. To explore whether the degree of pollen limitation primarily drives differences in mating systems and floral traits, we conducted a comprehensive study involving two closely related species, Halenia elliptica and H. grandiflora, in three sympatric sites. We investigated floral characteristics, pollinator visitation, pollen limitation, autonomous selfing ability, reproductive assurance and mating system in studied populations. Our findings show that H. elliptica produces smaller flowers and less nectar production than H. grandiflora, making it less attractive to pollinators. Compared with H. grandiflora, H. elliptica experienced more severe outcross pollen limitation, but compensates with a higher capacity for autonomous selfing, ensuring seed production under natural conditions. Moreover, significant differences in mating systems were detected between them, with H. elliptica exhibiting a higher selfing rate than H. grandiflora across all studied sympatric populations. These differences are also reflected in variations in herkogamy and dichogamy. Our study suggested that the degree of outcross pollen limitation impacts the divergence in mating systems and floral traits between sympatric closely related species, offering valuable insights into the evolution of plant mating systems and floral traits.