Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Freudenstein, John [1], Barrett, Craig [2].

Corallorhiza striata is a “double parasite” and the first case of sexually deceptive pollination known among North American orchids.

Angiosperms are known to have highly specific vegetative parasitic relationships with other plant and fungal species. Similarly, they can have highly specific relationships with animals that pollinate them. Cases of both situations are documented in orchids. It has been hypothesized that a single species would not be found engaging in both strategies because the situation would be evolutionarily unstable. We have found such a species, with high specify on both vegetative and reproductive axes, in Corallorhiza (Orchidaceae). Moreover, its pollination strategy is one of sexual deceit, the first reported from North America, and especially uncommon among epidendroid orchids. Corallorhiza striata is a leafless, mycoheterotrophic orchid with a broad distribution across North America. Along with C. bentleyi, a rare Appalachian endemic, it comprises the sister group to the remainder of the genus. Both C. striata and C. bentleyi target a very narrow range of fungi in Tomentella (Basidiomycota: Thelephoraceae) and have more highly deleted plastid genomes than other Corallorhiza, highlighting their obligate heterotrophy. Whereas other species in the genus are either selfing or pollinated by small hymenoptera or diptera, C. striata is pollinated by an ichneumonid wasp and we have evidence that a similar wasp at least visits C. bentleyi. These species differ from other Corallorhiza in the morphology of the labellum, being heavily thickened and bearing a single callus near the base rather than two narrow lamellae, and with the claw functioning as a hinge. This difference allows the labellum to move freely when landed on by the wasp, a very different situation than with other Corallorhiza, where the labellum is relatively immobile. They also differ from other Corallorhiza in having no mentum (a small, potentially nectar-producing spur). Given that C. striata and C. bentleyi do not produce nectar, we propose that this is an instance of sexual deception in pollination. We captured the fragrance emitted by C. striata and C. bentleyi and identified via GC-MS a single phenolic compound in both that may be a pheromone mimic. We analyzed the fragrance of another insect-pollinated species of Corallorhiza (C. odontorhiza var. pringlei) and found it dominated by aldehydes, suggesting a different fragrance strategy. In the sense that deceit pollination extracts a cost without reward to the pollinator, it can be viewed as a type of parasitism. Although it may be evolutionarily unstable in the long-term, such a doubly parasitic strategy can thus exist, providing a new window into highly specific ecological relationships.

1 - Ohio State University Herbarium, 1315 Kinnear Road, Columbus, OH, 43212, United States
2 - West Virginia University, Biology, 53 Campus Drive, Morgantown, WV, 26506, United States


Presentation Type: Oral Paper
Number: SYM1004
Abstract ID:442
Candidate for Awards:None

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