Pollinator functional group abundance and floral heterogeneity in an agroecological context affect mating patterns in a self-incompatible wild plant

Abstract

Premise: Restoration of seminatural field margins can elevate pollinator activity. However, how they support wild plant gene flow through interactions between pollinators and spatiotemporal gradients in floral resources remains largely unknown.

Methods: Using a farm-scale experiment, we tested how mating outcomes (expected heterozygosity and paternity correlation) of the wild, self-incompatible plant Cyanus segetum transplanted into field margins (sown wildflower or grass-legume strips) were affected by the abundance of different pollinator functional groups (defined by species traits). We also investigated how the maternal plant attractiveness, conspecific pollen donor density, and heterospecific floral richness and density interacted with pollinator functional group abundance to modulate C. segetum mating outcomes.

Results: Multiple paternity increased (=lower paternity correlation) with greater local abundance of hoverflies (syrphids) and female medium-sized wild bees (albeit the latter's effect diminished with decreasing maternal plant attractiveness), and the presence of male bumblebees (Bombus) under low local floral richness. Cyanus segetum progeny genetic diversity increased with male Bombus presence but decreased with greater abundance of syrphids and honey bees (Apis mellifera).

Conclusions: Overall, field margins supported plant-pollinator interactions ensuring multiple paternity and conservation of allelic diversity in C. segetum progeny. The contribution to plant mating outcomes of different pollinator functional groups was dictated by their local abundance or traits affecting pollen transfer efficiency. The local floral richness or maternal plant attractiveness sometimes modulated these relationships. This complex response of wild plant mating patterns to community interactions has implications for the use of field margins to restore functional pollination systems in farmed landscapes.

Keywords: Cyanus segetum [Asteraceae]; agroecology; cornflower; field borders; floral community; multilocus paternity correlation; plant breeding structure; plant‐pollinator interactions; pollinator functional groups; progeny genetic diversity.

Figure 1

Expected heterozygosity (Hs) in the progeny of Cyanus segetum maternal plants (n = 33) in relation to: (A) the local abundance of male Bombus; (B) the local abundance of syrphids; (C) the abundance of Apis mellifera in the local assemblage surrounding the maternal plant; and (D) the number of alleles of the maternal in the eight studied loci. Fitted lines (±95% CI) are partial residuals accounting for other fixed effects in the linear model (LM) explaining Hs. The scatter plots show the distribution of the raw data.

Figure 2

Multilocus (eight loci) correlation of paternity (rpm) in the progeny of Cyanus segetum maternal plants (n = 33) in relation to: (A) floral richness of the local assemblage × the local abundance of male Bombus; (B) the local abundance of syrphids; and (C) maternal plant relative attractiveness × abundance of female medium‐sized wild bees foraging in the surrounding floral assemblage. In A and C, warmer colors indicate greater values of rpm meaning lower numbers of pollen donors. The limits of the heatmap were specified to match the range of the observed data. In B, the fitted line (±95% CI) shows the partial residuals accounting for other fixed effects in the linear model (LM) explaining rpm and the scatter plot shows the distribution of the raw data.