Phenotypic selection in Geoblasta pennicillata: evolution of visual signals in an orchid pollinated by means of pseudocopulation.

BENITEZ-VIEYRA, S.; MEDINA, A.M.; COCUCCI, A.A.

Journal of Evolutionary Biology

Año: 2009 vol. 22 p. 2354 - 2362

By mimicking shape and female mating pheromones, flowers of sexuallydeceptive orchids attract sexually excited males which pollinate them whiletrying to copulate. Although many studies have demonstrated the crucialimportance of odour signals in these systems, most flowers pollinated bypseudocopulation resemble, at least superficially, an insect body and thesevisual cues may be important to cheat pollinators. In this 2-year study, weshow that the shape of the labellum of Geoblasta pennicillata is a target ofpollinator-mediated natural selection. Contrary to our expectations, plantswith a labellum shape more similar to female wasps were not favoured. Thestrength and pattern of phenotypic selection varied between study years andsexual functions. Although selection through female success was probablyassociated to the fine-tuning of the mechanical fit between flower form andmale wasp, shape was the target of natural selection through male success inboth study years indicating that male wasps use this trait when choosingflowers. The imperfect mimicry and patterns of selection observed indicatedthat an exact imitation is not needed to attract and deceive the pollinators andthey suggested a receiver perceptual bias towards uncommon phenotypes.