There’s no porn like an orchid flower

Orchids have the strangest and most fascinating blooms. Not that gardeners care. Not only that Darwin was right. But because orchids have their share of evolutionary master tricks. When it comes to reproduction, orchids always strike. You may remember how Epipactis helleborine produces a deceiving caterpillar scent to get its pollination service from wasps. Or the most widespread orchidean reproductive strategy: a flower mimicking their pollinator’s female (visually, but also via scenty insect sexual pheromones) and luring those poor male bees and wasps that desparately try to mate with a flower (usually reproducing the orchid, but not their own kind…).

Thus, many orchid flowers are just plain porn (to hymenoptera, I mean). But how far can the little critters be deceived in their mating attempt? In the Australian tongue orchids (Cryptostylis species) [1], the lure is working so far as to have their pollinators ejaculating on the flowers, and thus wasting precious gametes that would have otherwise well served them to an actual reproduction. One has to realise the cost of wasp porn… (though the abused wasps usually don’t get tricked twice).

This situation is nevertheless amazing, because luring males would lead to selection for increased discerning in wasp species (if you know how to tell a female from an orchid, you have higher reproductive success when competing with males who don’t). But this is typical evolutionary arms race, and when wasps evolve more prudent reproductive strategies, only the orchids that are best at luring reproduce, therefore increasing the efficiency of floral sexual deception. Turnaround.

What’s interesting in this co-evolving pair of species, it’s that pollinators are haplo-diploids. That is, unfertilised females still reproduce, but only produce haploid males (while they have female offspring when a regular fertilisation occured). Thus if males tends to waste gametes on orchids, there’s the risk of a sperm shortage in the population, leading to more male offspring produced… And more males means higher competition for mate and evolution of risk taking behaviours (and the orchid replenish its stock of naive pollinators…). Oh cycle!

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(1)- A.C. Gaskett, C.G. Winnick, and M.E. Herberstein (2008). Orchid Sexual Deceit Provokes Ejaculation. The american Naturalist 171(6):E206-212