Evolution of Organismal Female Wasp Mimics in Sexually Deceptive Orchid Genus Chiloglottis (Orchidaceae)

Abstract

Orchids are fascinating to the evolutionary biologists because of their spectacular flower structure, colours and specialized strategies in pollination. In 30,000 species of orchids, one third accomplishes pollination through deception by mimicking food, shelter and sexual partner of model insects. In sexual deception, orchids lure their pollinators by mimicking sex pheromone and by depicting the morphology of their model insects on the flower labellum. In Australian orchid genus Chiloglottis, occurrence of model’s (female sex of pollinator) sex pheromone mimicry for pollination through sexual deception is well established. However, the morphological evolution of calli structures on labellum representing model insect mimic in Chiloglottis is still a mystery. In this study, we qualitatively analysed the calli structures on the labellum in 21 species of the genus Chiloglottis and propose its evolution progressing from organ to organism level of the model with a few intermediate mimics in the ‘Darwinian Style’. From the qualitative analysis, we distinguish 3 groups of female wasp mimic evolution amongst 21 species as organ (parts of head and thorax, 8 species), intermediate (imperfect head and thorax, 8 species) and organism (head, thorax and abdomen, 5 species) level based on the arrangement of calli structures on the labellum. The labellum shape is found to have an association in the evolution of mimic structure, depicting cordate in organ level and spatulate or obovate or diamond shape in intermediate and organismal forms. Our results clearly indicate that the organismal form of insect mimics might have evolved from organ level in sexually deceptive orchids.