Effectiveness of diurnal and nocturnal pollination of two milkweeds

Abstract

The relative effectiveness of diurnal and nocturnal pollinators of two milkweed species, Asclepias syriaca and A. vcerticillata, was assessed experimentally and related to patterns of nectar production. Nocturnal pollinators inserted and removed fewer pollinia than diurnal vectors but caused equal pod set, and in A. syriaca, caused greater seed set. We suggest that observed peak nectar production patterns are adaptive in attracting nocturnal pollinators that may be of higher quality than diurnal species. This is one of the first attempts to compare the relative effectiveness of diurnal and nocturnal pollinators of any plant species. The excess of vector visits over that needed to obtain maximum pod set may allow selective abortion and (or) be adaptive in increasing reproductive success through pollinia donation.