Effects of floral restrictiveness and stigma size on heterospecific pollen receipt in a prairie community

Abstract

Plant species vary greatly in the degree to which floral morphology restricts access to the flower interior. Restrictiveness of flower corollas may influence heterospecific pollen receipt, but the impact of floral morphology on heterospecific pollen transfer has received little attention. We characterized patterns of pollinator visitation and quantities of conspecific and heterospecific pollen receipt for 29 species with a range of floral morphologies in a prairie community dominated by the introduced plant Euphorbia esula (leafy spurge) which has an unrestrictive morphology. Pollinator overlap was significantly greater between Euphorbia and other unrestrictive flowers than restrictive flowers. Compared to flowers with restrictive morphologies, unrestrictive flowers received significantly more Euphorbia pollen, more heterospecific pollen from other sources, and a greater diversity of pollen species, but not more conspecific pollen. However, stigmatic surface area was significantly larger for flowers with unrestrictive morphologies, and the density of Euphorbia and other heterospecific pollen per stigmatic area did not significantly differ between flower types. These findings suggest that the smaller stigma size in restrictive flowers partly accounts for their decreased heterospecific pollen receipt, but that restrictiveness also allows species to increase the purity of pollen loads they receive. Given that restrictive flowers receive fewer heterospecific pollen grains but at a higher density, the effect of restrictiveness on fecundity depends on whether absolute quantity or density of heterospecific pollen affects fecundity more. Our results also indicate that abundant neighbors are not necessarily important heterospecific pollen sources since Euphorbia pollen was rarely abundant on heterospecifics.

Heterospecific pollen transfer from an exotic plant to native plants: assessing reproductive consequences in an Andean grassland

“…E. vulgare and S. albicaulis) through chemical inhibitions (Wilcock and Neiland 2002). Our study showed that the presence of HP cannot be predicted from the presence of exotic plants alone, as has been reported previously (Montgomery and Rathcke 2012) and this suggests that pollen transfer may depend on flower morphology, with zygomorphic flowers (e.g. S. albicaulis) receiving less pollen than actinomorphic flowers (e.g.…”

“…On the one hand, the spatial distribution (Yang et al 2011), abundance (Lopezaraiza-Mikel et al 2007 and diversity (Ghazoul 2006) of plants are important factors for determining the constancy of pollinators to flowers; these factors could define the amounts of HP received by a focal species. On the other hand, flower morphology facilitates pollinator recognition and favours pollinator constancy in flowers, which reduces HP transfer (Schaefer et al 2004); additionally, flower morphology could act as a "barrier" to HP (Montgomery and Rathcke 2012;Ashman and ArceoGómez 2013). Specifically, HP deposit is less in bilateral flowers than in radial flowers (Montgomery and Rathcke 2012) because more open flowers are more susceptible to receiving pollen from different sources.…”

“…On the other hand, flower morphology facilitates pollinator recognition and favours pollinator constancy in flowers, which reduces HP transfer (Schaefer et al 2004); additionally, flower morphology could act as a "barrier" to HP (Montgomery and Rathcke 2012;Ashman and ArceoGómez 2013). Specifically, HP deposit is less in bilateral flowers than in radial flowers (Montgomery and Rathcke 2012) because more open flowers are more susceptible to receiving pollen from different sources. Secondarily, some characteristics of the pollen (e.g.…”

“…Although important progress has been made in understanding the effects of HP on plants (McLernon et al 1996;Montgomery and Rathcke 2012;Ashman and Arceo-Gómez 2013), understanding the effects of HP in the context of exotic species is still an open question; these plants could act as pollen donors to co-flowering native plant species. In this study we assessed whether the presence of an invasive plant, Echium vulgare (Boraginaceae) increased the presence of HP in two native herbs in central Chile, Phacelia secunda (Boraginaceae) and Stachys albicaulis (Lamiaceae), and incorporated the floral traits of natives as a covariable to disentangle their role in pollen deposition.…”

Insights from measuring pollen deposition: quantifying the pre-eminence of bees as flower visitors and effective pollinators

“…Ashman and Arceo-Gomez 2013;Fang and Huang 2013;Arceo-Gomez et al 2016a), though these studies highlight the great variation in HP deposition within individuals (range 0-95%) and species (range 0-80%), often linked to corolla and stigma morphology/size (e.g. Montgomery and Rathcke 2012). Effects of HP deposition on stigma interactions and the resultant success rates of conspecific pollen germination are highly varied between plants with obvious potential fitness costs for the plant (see Morales and Traveset 2008), and there may be particularly detrimental donors and particularly vulnerable recipients (Ashman and Arceo-Gomez 2013).…”