Does morphology matter? An explicit assessment of floral morphology in sexual deception

Sexually deceptive orchids are renowned for their olfactory mimicry of female insect sex pheromones to lure male pollinators, but the role of floral morphology remains unknown. Here, we reveal compelling new experimental evidence that morphology also matters in sexual deception. Our study exploited two morphologically distinct Chiloglottis orchids that both employ the same semiochemical (chiloglottone 1) to attract their respective primary pollinator. In these experiments, we monitored attempted copulation of pollinators with orchid labella as this likely impacts plant fitness. Reciprocal pollinator choice tests revealed significant reductions in the frequency and duration of attempted copulation when pollinators were presented with alternate orchid species that differ in floral morphology, but nevertheless exhibit identical semiochemicals. Experimentally shortening the labellum also reduced the duration of attempted copulation in one of the species. Pollinators exhibited contrasting orientations during attempted copulation and pollination, which seem to be correlated with fundamental differences in the morphological adaptations for both mechanical fit and female mimicry in these orchids. Our findings confirm the overlooked importance of floral morphology for sexually deceptive orchid pollination and indicate that pollinator behaviour could impose strong selection on specific floral traits.