“Getting lucky” as a flower requires a bit more tact than a courtship ritual given that plants are anchored to the ground and lack awareness as to where a suitable mate resides. Life in the Wet Zone, part of the Kindgom of Plants 3D series, examines some of the many tricks of the trade for sexual reproduction in orchids.

Over 90% of flowering plants rely on pollinators to do the heavy lifting when it comes to their successful reproduction, and this requires attracting a pollinator. In a world where populations of top pollinators, such as honey bees, are decreasing drastically, this is an increasing dilemma for plants. Other, however, long ago evolved complex mechanisms to maximize their chances of attracting a pollinator. The ever-clever orchid uses a simple trick to make sure that bees decide to spread their genes and not another orchid’s [1]. Charles Darwin himself marveled at the chicanery of some orchids after noting their rather unique way of attracting pollinators: mimicry.

Each orchid species has the amazing ability to mimic a member of its favorite pollinator’s species- be it bee, wasp, or fly. The insects then come to the plant hoping to find a mate. This sexual deception is the most effective and biologically efficient method to lure a pollinator and have it help in reproduction. But, bees have begun to recognize this trick, as attempting to breed with a plant hurts their chances of reproduction with a real mate. Some species have learned to avoid these mimickers in favor of partners not rooted in the ground [2]. The cunning aphid’s tricks don’t end there as they can fake more than just a look.

When a simple visual cue isn’t enough to attract a pollinator, orchids of use a series of volatile chemicals that can mimic anything from food to a female insect’s own hormones that indicate that she intends to mate. Much like visual deception, for each orchid species, the volatiles are limited to attracting one species of pollinator, and across the Orchidaceae some ten-thousand species of insects have been mimicked [3]. Both techniques, visual and chemical mimicry, have led to the flourishing of orchid’s in countless environments, as the evolutionary techniques of mimicry are strong enough to trick even the most discerning insect pollinator.

Success- an orchid tricks a wasp into mating with it and spreading its pollen, but this is only part of the story. Blooming up to two times a year for several years, the orchid must consistently trick pollinators into mating with it and keeping up the ruse can be costly. The energy cost of switching between mimics can be deadly for the plant, which leads most to exploit the same species year and after. A recent study has found a few discerning orchid species to be able to switch up their target audience and exploit multiple species over the course of just a few generation [4]. This just shows, as the animal kingdom continues to evolve so too will the plants in an effort to remain one step ahead. Just as the Red Queen said to Alice in Lewis Caroll’s Through the Looking-Glass, “Now, here, you see, it takes all the running you can do to keep in the same place.”

by Brandon Berryhill

Kingdom of Plants 3D, Life in the Wet Zone, starting at approximately 26:20

References

  1. Henneresse T & RA Wesselingh. 2017. Effects of floral display, conspecific density and rewarding species on fruit set in the deceptive orchid Orchis militaris (Orchidaceae). Plant Ecology and Evolution 150: 279-292
  2. Gervasi DDL, Selosse MA, Sauve M, Francke W, Vereecken NJ, Cozzolino S & FP Schiestl. 2017. Floral scent and species divergence in a pair of sexually deceptive orchids. Ecology and Evolution 7: 6023-6034
  3. Wong DCJ, Pichersky E & R Peakall. 2017. The biosynthesis of unusual floral volatiles and blends involved in orchid pollination by deception: current progress and future prospects. Frontiers in Plant Science 8
  4. Phillips RD, Brown GR, Dixon KW, Hayes C, Linde CC & R Peakall. 2017. Evolutionary relationships among pollinators and repeated pollinator sharing in sexually deceptive orchids. Journal of Evolutionary Biology 30: 1674-1692

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