Long‐tongued insects promote disassortative pollen transfer in style‐dimorphic Narcissus papyraceus (Amaryllidaceae)

Abstract

Summary In hermaphroditic flowers, reciprocal herkogamy, for example heterostyly, enhances pollen transfer between floral morphs (disassortative pollination) while avoiding self‐interference between sexual organs. By contrast, disassortative pollination might be compromised in style‐dimorphic flowers, which lack perfect reciprocity between the two floral morphs. This suboptimal functioning has been considered to explain why stylar dimorphism is rare in nature. Some style‐polymorphic species receive a wide array of floral visitors, including long‐tongued insects that feed on nectar and short‐tongued insects that feed on pollen. Differences in the morphology and behaviour of these two insect types could be manifested as different pollination patterns in each floral morph. By observing individual pollinators and pollen deposition and delivery in small field‐based experimental arrays with emasculated and intact flowers, we studied pollination patterns mediated by different insect types (long‐ and short‐tongued) in the two floral morphs (long‐ and short‐styled) of the style‐dimorphic Narcissus papyraceus. We investigated the patterns of pollen transfer between and within style morphs in cross‐pollinations, as well as self‐pollination and pollen removal rates, for each floral morph mediated by each insect type. Long‐tongued insects were efficient pollinators of both floral morphs as they removed little pollen from the anthers but deposited comparatively large amounts on the stigmas. Although disassortative pollen transfer and assortative pollen transfer were equally high to the long‐styled morph, the former prevailed in the short‐styled morph. Short‐tongued insects removed large amounts of pollen from the anthers but deposited only a few pollen grains on the long‐styled stigmas and a negligible number of grains on short‐styled stigmas regardless of the morph of the donor. Synthesis. In this study, we provide empirical support for the hypothesis that, under the action of long‐tongued pollinators, pollen transfer patterns in the stylar‐dimorphic Narcissus papyraceus resemble in part those of heterostylous species. In addition, we found that short‐tongued insects act mostly as pollen thieves, thereby limiting the male fitness of both style morphs, besides depleting the female fitness of S‐morph plants. In view of these results, we propose that the differing pollination efficiencies of floral visitors, in addition to their frequency, are key in determining the morph ratio of populations in this Narcissus.