Discovery of pyrazines as pollinator sex pheromones and orchid semiochemicals: implications for the evolution of sexual deception

Abstract

SummarySexually deceptive orchids employ floral volatiles to sexually lure their specific pollinators. How and why this pollination system has evolved independently on multiple continents remains unknown, although preadaptation is considered to have been important. Understanding the chemistry of sexual deception is a crucial first step towards solving this mystery.The combination of gas chromatography-electroantennographic detection (GC-EAD), GC-MS, synthesis and field bioassays allowed us to identify the volatiles involved in the interaction between the orchid Drakaea glyptodon and its sexually attracted male thynnine wasp pollinator, Zaspilothynnus trilobatus.Three alkylpyrazines and one novel hydroxymethyl pyrazine were identified as the sex pheromone of Z. trilobatus and are also used by D. glyptodon for pollinator attraction. Given that our findings revealed a new chemical system for plants, we surveyed widely across representative orchid taxa for the presence of these compounds. With one exception, our chemical survey failed to detect pyrazines in related genera. Collectively, no evidence for preadaptation was found.The chemistry of sexual deception is more diverse than previously known. Our results suggest that evolutionary novelty may have played a key role in the evolution of sexual deception and highlight the value of investigating unusual pollination systems for advancing our understanding of the role of chemistry in evolution.

Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

“…These compounds are rare and have been recorded in only a few plants [45,46], and may thus function as private channels of communication in the communities in which these cycads occur. The only previous report of attraction of a pollinator to a pyrazine compound involves a sexually deceptive Australian orchid that mimics the pyrazine sex pheromone of female thyniine wasps [47].…”

Deceptive Ceropegia dolichophylla fools its kleptoparasitic fly pollinators with exceptional floral scent

“…Floral scents usually advertise a food source provided by the flowers. In deceptive plants, however, flower scents are a false promise of a reward, such as food, a mating partner or an oviposition site (Salzmann et al, 2007;Jürgens et al, 2013;Bohmann et al, 2014) that these plants do not actually offer. Among these cheaters are plants of the genus Ceropegia L. (Apocynaceae, Asclepiadoideae) with more than 200 described species, characterized by sophisticated pitfall flowers (Vogel, 1961;Masinde, 2004).…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…They also have been found to attract bumblebees and honey bees (Granero et al 2005). Volatile terpenoids attract certain pollinators by releasing pheromones; for example, orchids employ floral scents that mimic a blend of pheromones from female pollinators, triggering copulation attempts by male pollinators with flowers (Bohman et al 2014). Tomato flowers in glasshouses mainly produce four monoterpenes (p-cymene, α-pinene, (+)-2-carene, and β-phellandrene); all of these are recognized as herbivoreinduced leaf volatiles, possessing toxic properties and functioning in plant defense.…”