Abstract Detail

Annals of Botany Lecture - Rod Peakall

Sexual deception in Australian orchids, insights on the evolution of extreme pollinator specialization and its reversibility.

While generalized pollination strategies are common in some groups of plants, 1000’s of plant species depend on one or a few pollinator species. For example, 100’s of sexually deceptive orchids depend on just a single pollinator species, with this extreme specificity likely a by-product of the sex pheromone mimicry they use to lure their pollinator. Although this pollination strategy is a worldwide phenomenon, with independent evolution on four continents, Australia is one major evolutionary center. Here, sexual deception has multiple origins within terrestrial orchids, and includes the sexual exploitation of males from five families of Hymenoptera and two families of Diptera. Our research has revealed that unusual semiochemicals, including many new to science compounds, are involved in pollinator attraction. For example, Chiloglottis orchids achieve specific wasp pollinator attraction via a novel class of compounds, called chiloglottones. Choice test bioassays further confirm that a single specific chiloglottone can elicit full pollinator behavior, while a similar chemical alternative fails. Surprisingly, chiloglottones are dependent on UV-B light for production, with new transcriptome evidence indicating gene duplication at specific fatty acid pathway genes hold the key to their biosynthesis and evolution. In further work, we have now confirmed that at least five distinct semiochemical systems are used by sexually deceptive Australian orchid genera to secure pollinator attraction. Notwithstanding the critical importance of these semiochemicals, experimental manipulations and selection analysis in Chiloglottis have also revealed strong evidence for pollinator-mediated stabilizing selection on floral size. Furthermore, experiments across genera have also revealed axes of floral trait variation that are expected to be under strong pollinator-driven selection. Collectively, these findings raise important questions on the evolution of the diverse chemical signals in the plant, on the chemical and morphological trade-offs imposed on the plant by specific pollinators, and on the roles of chemistry, morphology and pollinators in the speciation of sexually deceptive orchids. Ongoing research has shifted attention to Caladenia, the most diverse terrestrial orchid genus in Australia (350+ species), and the only known genus in the world using pollination by food reward, food deception and sexual deception. Exciting emerging results indicate that the evolution of sexual deception from ancestral food deception underpins diversification, but that repeated reversals have enabled new radiations with more generalized pollination. Thus, unexpectedly, extreme pollinator specialization is reversible in Caladenia, offering new insights of relevance worldwide on the evolution of extreme pollinator specialization and its reversibility.

1 - The Australian National University, Ecology and Evolution, Research School of Biology, Canberra, ACT, 2600, Australia

Keywords:
pollination
semiochemicals
specialization
plant-pollinator interactions
Natural Selection.

Presentation Type: Special Presentations
Session: S06, Annals of Botany lecture - Live Rod Peakall
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 4:00 PM
Number: S06001
Abstract ID:231
Candidate for Awards:None