Shhhh... Let Him Finish

Sexual deception is rampant in the orchid family. Orchid genera all over the world produce flowers that trick sexually charged male insects into failed mating attempts. The orchids go to great lengths to resemble females both in appearance and smell. Indeed, many sexually deceptive orchid species emit odors that precisely mimic the pheromones of specific insect species. 

In many instances, the orchids ruse is so powerful that male insects will often preferentially visit the flower over an actual female. For many of the sexually deceptive orchids, all that is required is the male to pay a visit. No attempt at copulation is necessary, though that doesn't stop vigorous attempts. Because of this, it is easy to see how the minute cost incurred to the insects is not enough to drive evolution away from deception. However, there is a group of tongue orchids (genus Cryptostylis) from Australia that seem to throw a wrench into this finely tuned system.... or do they?

The tongue orchids rely on deceiving male wasps in the genus Lissopimpla into mating with their flowers. As mentioned above, the males simply cannot resist the attempt. However, unlike many other reported cases, the male wasps actually mate to completion, depositing their sperm onto the flower. This should be disastrous for the wasps since males not only prefer flowers to wasp females, but they also waste their precious few mating attempts. How could this have evolved?

Most sexually deceptive orchids rely on bees and wasps (family Hymenoptera) for their pollination. Thus, the answer to this evolutionary conundrum lies in the mating system of these insects. Queens are genetically haplodiploid. I will spare you the details on that but basically what it means for Hymenoptera is that female offspring are produced via fertilized eggs whereas male offspring are produced via unfertilized eggs. 

The orchids have (unknowingly of course) tapped into this system to their benefit. If by mating with the flower and not a female wasp meant that no offspring were produced, this system surely would not have evolved to the level that it has. Instead, female wasps that have not been mated with or received less sperm than usual end up producing a higher amount of male offspring.

The orchids are effectively skewing the sex ratio of their pollinators! "How is this a sustainable system?" you may be asking. Well, by causing female wasps to produce more males, the orchids are ensuring that there will be more naive males in the population the next time they are in bloom. Also, by skewing the sex ratio towards males, there are now fewer females to mate with so that males become less choosy and more readily mate with orchids. Finally, with more sexually charged males flying around, each female has a greater chance of being fertilized. Because of the unique mating system that has evolved in Hymenoptera, the orchids have thus been able to evolve this pollination strategy with little harm to the pollinators.

Photo Credit: photobitz

Further Reading:
http://instructional1.calstatela.edu/kfisher2/BIOL360/classroom.activities/species_interact._casestudies/orchid.sex.pseudo.II.pdf

An Orchid Invader With an Interesting Ecology

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Orchids are notoriously finicky about where they will grow. The family with which they belong (Orchidaceae) may be the most diverse plant family in the world. Because of this massive diversity, orchids have become quite specialized plants. Orchids hedge their reproductive success on production of millions upon millions of tiny, wind-blown seeds. With seeds so tiny there is not much room left to equip them with food in the form of nutrient packed endosperm (the stuff you are eating when you eat coconut) and thus orchid seeds rely on specific species of fungi in order to germinate. Some orchids take this relationship to the extreme but that is a post for another day. Because of all this specialization, orchids are a pretty vulnerable group of plants. Most species are threatened because of poaching and habitat loss and many are endangered. This is why coming across the plant I am writing about may seem shocking.

I am talking about the helleborine orchid (Epipactus helleborine) which originally hails from northern Eurasia. I first came across this plant down on some Nature Conservancy land in Gowanda, NY. This was a few years ago and I did not recognize it for what it was. Over the past few years however, I began seeing this plant in the strangest places including areas in the City of Buffalo with amazingly poor soil. I was lucky to have a few start growing in the garden so watching them develop was fun and easy. They are a very nice looking plant, standing about 7 to 8 inches high. The flowers are readily recognizable as belonging to an orchid and each plant produces a spike full of them.

In its immature stage this plant germinates and grows as an underground rhizome and is considered fully mycoheterotrophic, which means it tricks mycohrrizal species of fungi into associating with it then feeds off of the nutrients that the fungi gain from trees. The orchid can stay in this state of growth for upwards of 10 years before it has enough energy to flower. When the right conditions are present it then begins its adult phase of growth. It throws up a stem, some leaves, and flower buds. At this point it can begin making its own food through photosynthesis but will still use the fungi as well.

Once it begins to flower it then needs to call on the help of wasps for pollination. There has been some amazing research done on how it achieves this. Apparently the plant begins to release compounds called "green-leaf volatiles" or GLV's. Plants such as cabbage produce GLV's when damaged by insects in order to attract wasps that will either lay eggs in/on the insects or take them back to their hive. This is not the orchid's goal. Instead, when the orchid produces GLV's, its doing it for sex. INterestingly enough, the flowers apparently have not evolved structurally sound methods for pollination. Because of this, they utilize yet another ruse.

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Once the wasps get there they are "encouraged" to stick around in a very unique way. There are reports that the flowers produce narcotic drugs and alcohols that dope up the wasps, which causes them to linger and stumble around the flower thus increasing the chance of picking up a pollinia. This process then gets repeated each time a wasp visits another flower. Thus, pollination is achieved.

This plant is a reminder that even invaders are worth a closer look. The fungi that the helleborine orchid partners with are a group of disturbance-loving truffles (not the kind you eat) and therefore can most often be found in close proximity to humans. Keep an eye out for this species. Make sure to spend some time examining this plant for all its worth.

Further Reading:

http://link.springer.com/article/10.1007/s00606-002-0197-x?no-access=true

http://blogs.discovermagazine.com/notrocketscience/2008/05/12/orchid-lures-in-pollinating-wasps-with-promise-of-fresh-meat/#.Va8HhipVikp

http://www.cell.com/current-biology/abstract/S0960-9822(08)00526-5