Deceptive pollination of orchids
Zongxin Ren, Hong Wang, Yibo Luo
Biodiv Sci. 2012, 20 (3):
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Mutualism, or a mutually beneficial interaction between two organisms, are ubiquitous in ecological systems. However, some “empty flowers”, which offer pollinators no any kinds of rewards, design different strategies to attract pollinators without providing rewards to the pollinators. These pollination mechanisms are called deceptive pollination. The family Orchidaceae, representing one of the largest groups in angiosperms, is distinguished by high floral diversity and intricate adaptations to pollinators. Darwin described and identified most of the functional floral morphology and biomechanics in orchid pollination. However, he never recognized that many of the flowers that he examined lacked food rewards for pollinators. Floral evolution in the Orchidaceae appears to be dominated by modes of deceptive pollination, and more than one third of orchid species are thought to be pollinated by deceit. Deceptive pollination is thought to be one of key roles which has lead to relatively high species diversity within the Orchidaceae. Deceptive orchids frequently exploit the food foraging, sexual, oviposition and sleep/warmth behaviors of insects. The most common deception mechanisms include generalized food deception, Batesian floral mimicry, sexual deception, brood-site imitation and shelter imitation. Additionally, floral color, morphology and fragrance play key roles to cheat target pollinators. Relationships between deceptive orchids and their pollinators possibly involve asynchronous evolution; therefore orchids track the diversification of their pollinators. However, deception has negative impacts on the pollinators, which may exert selection on the pollinators. Because duped pollinators tend to avoid rewardless flowers, deceptive orchids suffer low visitation rates and fruit set, various environment factors can affect the reproductive success of these orchids. Deceptive orchids depend largely on insect pollinators for reproduction, and the proclivity of these species to use deceptive pollination strategies puts many of these species at a relatively higher rate of extinction. Therefore, pollination biology studies are needed to provide a scientific basis for proper conservation of orchids. At the community level, co-occurring mimic, non-mimic, and mimic signal providing plant species affect the reproductive fitness of orchids. Therefore, it is necessary to further study the co-evolution webs of deceptive orchids and pollinators along with other related biological and ecological factors.