Three Chemically Distinct Floral Ecotypes in Drakaea livida, an Orchid Pollinated by Sexual Deception of Thynnine Wasps.

Alyssa M Weinstein,Björn Bohman,Gavin R Flematti,Ryan D Phillips

doi:10.3390/plants11030260

Abstract

Sexually deceptive orchids are unusual among plants in that closely related species typically attract different pollinator species using contrasting blends of floral volatiles. Therefore, intraspecific variation in pollinator attraction may also be underpinned by differences in floral volatiles. Here, we tested for the presence of floral ecotypes in the sexually deceptive orchid Drakaea livida and investigated if the geographic range of floral ecotypes corresponded to variation in pollinator availability. Pollinator choice trials revealed the presence of three floral ecotypes within D. livida that each attracts a different species of thynnine wasp as a pollinator. Surveys of pollinator distribution revealed that the distribution of one of the ecotypes was strongly correlated with that of its pollinator, while another pollinator species was present throughout the range of all three ecotypes, demonstrating that pollinator availability does not always correlate with ecotype distribution. Floral ecotypes differed in chemical volatile composition, with a high degree of separation evident in principal coordinate analysis. Some compounds that differed between ecotypes, including pyrazines and (methylthio)phenols, are known to be electrophysiologically active in thynnine wasp antennae. Based on differences in pollinator response and floral volatile profile, the ecotypes represent distinct entities and should be treated as such in conservation management.

Highlights

One of the most specialised pollination strategies is that of sexual deception [1,2], in which pollination typically occurs via sexual attraction of male insects to a flower through chemical mimicry of female sex pheromones [3,4,5,6,7]
Despite Catocheilus sp. being a confirmed pollinator of D. livida [42,48], no wasps of this species were observed flipping the hinge of D. livida [42,48], no wasps of this species were observed flipping the hinge of flowers belonging to this putative ecotype
In accordance with the hypothesis that D. livida is comprised of floral ecotypes, the results of pollinator choice trials indicate that three distinct ecotypes are present in D. livida, each defined by different pollinator responses

Summary

Introduction

One of the most specialised pollination strategies is that of sexual deception [1,2], in which pollination typically occurs via sexual attraction of male insects to a flower through chemical mimicry of female sex pheromones [3,4,5,6,7]. Due to the high specificity of insect sex pheromones, sexually deceptive orchids frequently have only a single pollinator species, with closely related orchids typically exploiting different pollinator species [12,13,14,15,16]. Related sexually deceptive orchids often attract pollinators using structurally similar semiochemicals (pheromones or other inter-organism signalling compounds). To attract thynnine wasp pollinators, co-occurring Chiloglottis species use different combinations of one or two compounds out of a pool of structurally similar cyclohexanediones (chiloglottones) [6,14]. Most European Ophrys studied to date attract native bees as pollinators using different blends of alkanes and alkenes, with an overlap in compounds between orchid species [7,17,18,19]. In the Australian genus Caladenia, two species use (methylthio)phenols to attract Campylothynnus pollinators [21,22], while another species attracts a member of a different wasp genus, Zeleboria, using a monoterpene and an acetophenone [23]

Methods

Results

Conclusion