Avoiding sexual interference: herkogamy and dichogamy in style dimorphic flowers of Narcissus broussonetii (Amaryllidaceae)

Abstract

Spatial (herkogamy) or temporal (dichogamy) separation of sex organs are mechanisms considered to restrict self-pollination and promote outcrossing. Additionally, avoidance of self-interference is proposed to be the driving force for the evolution of these mechanisms, particularly in self-incompatible species. However, species with anthers and stigmas at different levels may increase the rate of imprecise pollen transfer, resulting in pollen discounting. Non-reciprocal stylar dimorphism has been considered a transitional, unstable stage towards the evolution of reciprocal style dimorphism (distyly), to simultaneously avoid interference and lack of precision. In this study we investigate the spatial and temporal separation of sex organs in a population of the style dimorphic and self-incompatible Narcissus broussonetii and their consequences in the reciprocity between the sex organs of morphs and their fecundity. First, we evaluated the relative growth of sex organs after anthesis. Then, we studied the stigma receptivity along the flower lifespan including its effect on seed production in both morphs. Finally, given the weak reciprocity between the sex organs of morphs of this species, we estimated population genetic diversity parameters in Long- and Short-styled plants to explore differences between them as a result of rates of inbreeding due to different mating strategies. We observed that Long-styled plants and Short-styled plants present different strategies to avoid sexual interference and both of them had negative consequences in the reciprocity between the sex organs of morphs. Long-styled plants exhibited a delay in stigma receptivity and a higher growth rate of the style after anthesis, while Short-styled plants presented higher herkogamy and no delay in stigma receptivity. These findings suggest that the avoidance of self-interference, in stylar dimorphic Narcissus species, seems to be more critical than improving of reciprocity between the sex organs of morphs. This might explain why reciprocal herkogamy (distyly) is rare in the genus.

Inter‐morph pollen flow and reproductive success in a self‐compatible species with stigma‐height dimorphism: the influence of herkogamy and reciprocity

“…Studies on species with stigma-height dimorphism, especially of the genus Narcissus, have underscored the importance of avoiding sexual interference and self-pollination in maintaining this polymorphism, as compared to increasing reciprocity (Cesaro et al 2004;Ferrero et al 2017). In fact, it has also been proposed as one of the drivers for the evolution and predominance of stigma-height dimorphism in this genus (Cesaro et al 2004;Sim on-Porcar 2018;Barranco et al 2019). Physiological incompatibility acts in concert with herkogamy to avoid selfing.…”

“…Studies in heterostylous species show that higher herkogamy is related to decreased self-pollination (Nishihiro & Washitani 1998), as well as increased inter-morph pollen transfer and reproductive success (Hernandez & Ornelas 2007;Keller et al 2014;Liu et al 2016). Similarly, evidence from a small number of studies suggests that herkogamy also increases reproductive success in species with stigma-height dimorphism (Cesaro et al 2004;Barranco et al 2019). A key difference in the functional significance of herkogamy in heterostylous species, as opposed to species with stigma-height dimorphism, is that in the former, herkogamy is usually accompanied with heteromorphic incompatibility to ensure inter-morph mating.…”

Morph-specific patterns of sex organ positions in species with style length polymorphism

“…Understanding differences in sex organ heights between morphs has been a central subject of various studies on heterostylous species (Thompson & Dommee, 2000;Kudoh et al, 2001;Kálmán et al, 2007). Differences in herkogamy between morphs have been reported for a lot of species with distyly and stigma-height dimorphism (Thompson & Dommee, 2000;Cesaro et al, 2004;Li et al, 2010;Liu et al, 2012;Faife-Cabrera, Ferrero, & Navarro, 2014;Novo et al, 2018;Barranco, Arroyo, & Santos-Gally, 2019). Such differences between morphs are associated with differences in inter-morph pollen transfer due to avoidance of self-and intra-morph pollination (Baena-Díaz et al, 2012;Keller et al, 2014).…”

Late-acting self-incompatible system, preferential allogamy and delayed selfing in the heteromorphic invasive populations ofLudwigia grandiflora subsp. hexapetala

“…The copyright holder for this preprint this version posted July 15, 2021. ; https://doi.org/10.1101/2021.07.15.452457 doi: bioRxiv preprint architecture of a flower, Barranco et al 2019), sometimes associated with additional features such as differences in pollen sizes and shapes, and different lengths of stigmatic papillae (Barrett and Shore 2008). Commonly, species with style polymorphism have a sporophytic heteromorphic (i.e.…”

“…Heterostyly defines the occurrence in a species of two or three floral morphs (di-and tristyly) that exhibit reciprocal herkogamy (spatial distancing of the anthers and stigma in the 3D architecture of a flower, Barranco et al 2019), sometimes associated with additional features such as differences in pollen sizes and shapes, and different lengths of stigmatic papillae (Barrett and Shore 2008). Commonly, species with style polymorphism have a sporophytic heteromorphic (i.e.…”