Sexually deceptive orchid pollination strategies: is one true love or broad sex appeal best?

Project Highlights:
- Work on sexual deception, a pollination strategy unique to orchids, arguably the most charismatic of flowers
- Use Britain's unique ecological history as an opportunity to assess pollination strategies and conservation issues
- Use the latest techniques to analyse pheromones and colour and answer questions about pollination strategies and the evolution of trickery
Overview:
Sexually deceptive orchids achieve pollination by mimicking the pheromones and appearance of female insects. The orchids entice males to try to mate with the flowers and pollen is spread through repeated deception among flowers. In this way orchids avoid the costs of producing nectar, but mimicking pheromones and colour is presumably expensive. Sexually deceptive orchid species vary in the number and diversity of pollinator species they attract, ability to self-pollinate, and if they share pollinators with other species.
It is not known how these different strategies affect pollination success, plant abundance and the population resilience of these often-vulnerable species. Is it better to mimic one pollinator or several? Is it too expensive to mimic several species perfectly, but imperfect mimicry is enough? And when a pollinator becomes locally extinct, releasing a species from a specific selection pressure, are deceptive traits no longer maintained?
There are four species of the sexually deceptive orchid genus Ophrys in Britain, all of which also occur Specifically, this project aims to:
1. Determine the impacts on mimicry of losing selection pressure when a pollinator becomes extinct
2. Measure and compare how closely orchids mimic insects when they mimic one versus many pollinators
3. Quantify the reproductive success of different strategies
4. Use cost-benefit analysis to assess which strategy leads to more resilient populations
Fig 1. Ophrys apifera (left) is pollinated in Europe by a single bee species, which is absent in Britain resulting in solely self-pollination. In contrast, Ophrys insectifera does not self-pollinate but attracts three pollinators from two genera in two insect orders.
Quantification of the costs and benefits of floral sexual deception will benefit the scientific community by contributing answers to long-standing questions about evolutionary mechanisms. This system will be a useful model for plant-pollinator interactions, and particularly for the evolution of trickery in nature. By better understanding pollinator strategies of native orchids, this project could contribute to their
conservation, which is particularly import given the vulnerable status of some of the species.
Methods:
Measuring the colour, shape and scents released by the orchid species and their pollinators will allow quantification of the strength of the mimicry, by comparative analysis among species and populations.
Monitoring orchid reproductive output will assess strategy success. Scent will be quantified by condensing volatiles collected from plants in situ, and from their insect pollinators, for analysis in a mass spectrometer. Floral and insect colour will be analysed with conventional digital camera photos using new analysis tools. Reproductive success can be measured by counting the large capsules that house the tiny seeds without the need for collection. These methods allow for many measurements without damage to plants, as some of the species are listed as vulnerable in the UK. By comparing between populations and species with different pollinators, this project will quantify the costs and benefits of deceiving one versus multiple pollinators. We will determine how a species responds to a relaxation of selective pressure by comparing populations of Ophrys apifera in locations with and without a pollinator (United Kingdom and France).