Morph ratio variation and sex organ reciprocity in style-dimorphic Narcissus assoanus

Abstract

The maintenance of floral polymorphisms depends on rates and efficiency of cross-pollination within and among mating types in relation to their relative frequency. Here, we examine whether stigma-anther reciprocity in style-dimorphic Narcissus assoanus (populations show either 1: 1 ratios of long-styled [L-morph] and short-styled [S-morph] plants or significantly L-morph-biased ratios) is correlated with morph ratio variation and whether such differences affect female fitness. In a natural population we created experimental plots of S-morph maternal plants and quantified their female fertility in the presence of either L-morph donors or S-morph donors with only their lower anther levels (we emasculated upper-level anthers).We also quantified floral traits and reciprocity in the positions of stigmas and anthers in 30 natural populations across the species' geographic distribution. We found an increase in seed set on maternal S-morph plants in the presence of L-morph donors and patterns of trait variation that may contribute to enhanced reciprocity with increasing frequency of the S-morph. Subtle differences in the position of sex organs affect pollen transfer and are correlated with morph ratio variation, indicative of frequency-dependent selection.