An experimental evaluation of self‐interference in Narcissus assoanus : functional and evolutionary implications

Floral traits that reduce self‐pollination in hermaphroditic plants have usually been interpreted as mechanisms that limit the genetic consequences of self‐fertilization. However, the avoidance of sexual conflict between female and male function (self‐interference) may also represent an important selection pressure for the evolution of floral traits, particularly in self‐incompatible species. Here, we use experimental manipulations to investigate self‐interference in Narcissus assoanus , a self‐incompatible species with a stigma‐height dimorphism in which the degree of spatial separation between sex organs (herkogamy) differs strikingly between the long‐ and short‐styled morphs (hereafter L‐ and S‐morphs). We predicted that weak herkogamy in the L‐morph would cause greater self‐pollination and hence self‐interference. Experimental self‐pollination reduced seed set when it occurred prior to, or simultaneously with, cross‐pollination in the L‐morph, but only if it occurred prior to cross‐pollination in the S‐morph. In the field, autonomous self‐pollination was greater in the L‐morph than the S‐morph, but we found no evidence that self‐interference reduced maternal or paternal fitness in either morph. One‐day‐old flowers of the L‐morph have reduced stigma receptivity and hence exhibit protandry, whereas stigma receptivity and anther dehiscence are concurrent in the S‐morph. This suggests that the two style morphs have alternative strategies for reducing self‐interference: dichogamy in the L‐morph and herkogamy in the S‐morph. These results provide insight into the mechanisms that reduce sexual conflict in hermaphrodite plants and are of significance for understanding the evolution and maintenance of sexual polymorphisms.