Gender‐specific pollinator preference for floral traits

Abstract

Summary Shifts between alternative pollinator types are regarded as the main source of divergent selection underlying angiosperm floral diversification. However, pollinating species can exhibit substantial intraspecific variation, particularly between genders, in key morphological and behavioural traits determining their interactions with flowers. This potential mechanism of floral diversification remains largely unexplored. The bee fly, Megapalpus capensis, is the predominant pollinator of the remarkable array of floral forms of the sexually deceptive daisy Gorteria diffusa. Flies exhibit strong gender‐specific interactions with the variable insect‐like spots which characterize G. diffusa inflorescences. In order to explore variation in the preferences of male and female pollinators for the visual, tactile and olfactory components of these spots, and its implications for floral diversification, we used a sequence of binary choice tests where we manipulated individual spot components. Male and female flies exhibited contrasting preferences for spot components with females preferring simplistic spots and avoiding UV highlights, whilst males prefer any additional visual and tactile phenotypic complexity. Floral odour alone elicited significant preference in females only, indicating that, in contrast to orchids, sexual deception in G. diffusa is achieved largely through visual mimicry of female pollinators. Our results clearly show that elaboration of the insect‐like spots has evolved in response to male preferences and suggest that a trade‐off exists between the attraction of male and female flies, which may have contributed to the divergence in floral phenotype between morphotypes of G. diffusa Pollinators exhibit gender differences in floral preferences and behaviour which is another potential source of divergent selection contributing to angiosperm floral diversification.