Gender‐specific pollinator preference for floral traits

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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. 5. 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. 6. 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. 7. Pollinators exhibit gender differences in floral preferences and behaviour which is another potential source of divergent selection contributing to angiosperm floral diversification.

Floral trait variation and integration as a function of sexual deception inGorteria diffusa

“…figure 5 include divergence between forms in the ratio of spot edge to middle spot length despite similar correlation of these traits within all floral forms (figure 5c; ANCOVA interaction term F 9,356 ¼ 1.21, p . 0.05), and divergence between the Spring and Okiep forms and the rest in relative positioning of UV and three-dimensional structures (both important for attraction of male flies) [27] on the spot despite similar within-floral-form correlation (figure 5d; ANCOVA interaction term F 6,243 ¼ 0.72, p . 0.05).…”

“…Although both male and female flies visit and pollinate G. diffusa, males tend to prefer more complex spots [27] and often attempt to copulate with the spots of the most complex forms, resulting in increased pollen export [31]. The fly-mimicking spots typically contain specialized, three-dimensional papillate structures and UV reflective highlights that are important in deception, as they attract male, but not female flies [27]. Not all floral forms are engaged in sexual deception, however, and some forms interact with other aspects of M. capensis behaviour, such as sleeping and feeding activities (AG Ellis 2012, unpublished data).…”

“…M. capensis is the main pollinator of all forms of G. diffusa [28]. Although both male and female flies visit and pollinate G. diffusa, males tend to prefer more complex spots [27] and often attempt to copulate with the spots of the most complex forms, resulting in increased pollen export [31]. The fly-mimicking spots typically contain specialized, three-dimensional papillate structures and UV reflective highlights that are important in deception, as they attract male, but not female flies [27].…”

“…(Asteraceae). Here, the primary component of attraction appears to be a mimetic suite of visual traits [27].…”

“…Spot traits (10 traits; e-n, figure 2(i)(iii)(iv)), which are involved in visual mimicry of female flies [27], were treated as a separate trait module in analyses. Unlike the mimicry traits (spot traits) which are exclusively on ray florets, traits which are not directly involved in fly mimicry were measured across ray and disc florets.…”