To deceive or not to deceive

Posted by Emma Bodley (Twitter @ebodley)

When you think of an orchid what usually comes to mind are the beautiful showy plants such as the moth orchids that most people have on the dining room table or in the guest bathroom.

Phalaenopsis_amabilis_Orchi_03

A moth orchid, by Orchi – Self-photographed, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3126890

In the research world these are also the same orchids that get all the attention. But the New Zealand orchid diversity is more understated, usually terrestrial green plants blending into the forest floor. As ecologists we know very little about NZ orchids in general and there are many forms that are yet to even be formally named.

Our recently published paper reveals some of the secrets about the

greenhood flower

The greenhood orchid Pterostylis brumalis

phenology and pollination system of one native greenhood orchid Pterostylis brumalis. What pollinates them? How do their pollinators know where the orchids are? Do they use sexual deception – tricking male pollinators into visiting the flowers like some other orchid species do?

We followed the phenology of this winter-flowering orchid closely, trapped for pollinators using sticky traps and assessed the natural seed set of a population. Problem was, pollination was extremely limited in the two populations we studied. We only collected only one insect, a female fungus gnat, that had interacted with a flower and was carrying pollen. As a consequence, natural fruit-set was low, averaging only 2.6%. In contrast, when we hand-pollinated flowers we achieved 66.7% fruit-set. It remains a mystery as to what naturally pollinates this species.

One of the harder areas to investigate is the theory of sexual deception in greenhoods. Usually orchids that trick male pollinators into visiting their flowers produce a scent that mimics that of a female. We wanted to look for evidence in the flowers that this is a possible mechanism for attracting male pollinators. Studying the colour and micromorpholgy of the flower showed some interesting features. We were looking for scent glands where the scent could be released from. We found some hairs that could perform this function, but most likely guides the pollinators into the centre of the flower down to the pollen. We didn’t find sufficient evidence to prove that sexual deception is really happening in this system. There are still plenty of avenues to research to get a better understanding of orchid pollination.

SEM greenhood orchid.PNG

SEM images of Pterostylis brumalis. A, Lateral sepal tip; B, labellum; C, labellum; D, trichomes on labellum.

Bodley, E., Beggs, J., Toft, R., & Gaskett, A. (2016). Flowers, phenology and pollination of the endemic New Zealand greenhood orchid Pterostylis brumalis. NZ J Bot, 1-20.
Emma2

This research was undertaken while Emma Bodley was an MSc student at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland. She successfully completed her study and is now a Botanical Records and Conservation Specialist at Auckland Botanic Gardens. She was supervised by Anne Gaskett and Jacqueline Beggs.

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