The effects of inbreeding depression and pollinator visitation on the maintenance of herkogamy in Oxalis corniculata, a species derived from a heterostylous ancestor

Abstract

The evolutionary transition from outcrossing in heterostylous morphs to selfing in homostylous morphs has occurred in many plant lineages. Homostylous variants with a low degree of herkogamy may increase the reproductive advantage of autonomous self-pollination when there is little inbreeding depression and/or low pollinator visitation. Oxalis corniculata, a self-compatible perennial herb derived from a tristylous ancestor, is reported to have two floral morphs. Homostyled plants are broadly distributed in Japan, whereas longstyled plants are reported to occur only in coastal areas. We examined the hypothesis that a reproductive advantage in avoiding inbreeding depression and/or frequent pollinator visits enables long-styled plants to live in some areas.Studies on floral variation revealed that the degree of herkogamy varied widely and continuously within and among populations. Homostyled and long-styled morphs were functionally defined based on the ability of autonomous selfpollination. Homostyled plants were widely distributed, whereas long-styled plants were found in and around the two coastal populations and relatively inland populations. Pollination experiments provided no evidence of inbreeding depression in either homostyled or long-styled plants. Pollinator visitation frequency was higher in the two coastal populations than in the other populations. Thus, reproductive disadvantage in long-styled plants lacking autonomous selfpollination has reduced in the two coastal populations, and long-styled plants may be maintained due to a competitive advantage of large seed size. In contrast, we recorded no comparable frequencies of pollinator visitation in other populations containing long-styled plants, indicating that there are other factors contributing to the maintenance of long-styled plants in these areas.

Diverse mating consequences of the evolutionary breakdown of the sexual polymorphism heterostyly

“…Such mixed mating differs from the predominant selfing that characterizes homostyles in the well-studied P . vulgaris ( 21 , 48 , 49 ) and other heterostylous lineages ( 13 , 36 , 50 ). In the two monomorphic P. oreodoxa populations, most offspring from H plants resulted from self-mating, but with appreciable (30 to 37%) outcrossing.…”

“…1 ). For simplicity, we have outlined the possible expectations in the context of transitions from classical distyly, although they apply similarly to the breakdown of tristyly ( 35 , 36 ). During these transitions, populations could differ in the proportions of the ancestral, highly herkogamous, heterostylous morphs as well as phenotypes with reduced herkogamy, as observed in some self-compatible Primula species ( 37 ), depending on their pollination environments.…”

Floral morph variation mediated by clonal growth and pollinator functional groups of Limonium otolepis in a heterostylous fragmented population

“…The classical homostyly has attracted considerable attention in the evolution of heterostyly ( Jiang et al 2018 ; Wang et al 2020 ; Charlesworth 2023 ; Mora-Carrera et al 2023 ). It occurs frequently and is often accompanied by the breakdown of incompatible heteromorphic systems ( Ganders 1979 ; Barrett 1992 ; Barrett and Shore 2008 ; Cohen 2010 ; Huu et al 2016 , 2022 ; Hoshino et al 2022 ). In the L. otolepis population, based on the floral traits and the self-incompatibility relationship between floral morphs, H-morph flowers differed from the classical homostyly reported.…”