Orchids mimic alarm pheromones of bees to attract wasps

At the end of The Origin, Darwin constructed a justly famous metaphor of nature as a “tangled bank.” In the case of mimicry, the metaphor might be Walter Scott’s “tangled web,”* since the network of interspecific interaction and deception can become quite intricate. Some of the most famous examples of mimicry are those of orchids that mimic bees and wasps.

Natural selection has molded the flowers of these orchids (many in the genus Ophyrys) into mimics of the insects that pollinate them. Horny male insects, thinking that the petals are a female, land on them and engage in fruitless attempts to copulate (“pseudocopulation”). During the barren act, the insects’ heads or bodies contact the orchids’ pollen sacs, which break off and attach to the insect. The frustrated insect flies off, but soon tries to copulate with another orchid, which puts the hitchhiking pollen in contact with the new orchid’s stigma. In such a way the bees/wasps serve as “flying penises,” helping the orchids have sex. Here are some specimens:

Ophrys insictiferaFig. 1. Ophyrys insectifera (fly orchid), which deceives male digger wasps.

Mirror orchid

Fig. 2. Mirror orchid (Ophrys speculum), which attracts scolid wasps.

By adopting the “female mimic” strategy, the orchid sacrifices half its potential pollinators (the female bees/wasps), but there’s no obvious way to attract a coy female insect.

Here’s a David Attenborough video showing pseudocopulation of a mirror orchid by a wasp. As Attenborough notes, the orchids also have olfactory mimicry of the wasp: they produce a chemical similar to the mating pheromone of the female wasp, further increasing the flower’s allure. (This form of mimicry was recognized only recently since it is far less obvious than the visual similarity).

In a new paper in Current Biology, Jennifer Brodman and her coauthors show that a Chinese orchid, Dendrobium sinese, has an even more intricate strategy for attracting wasp pollinators. Rather than mimicking the wasp’s mating pheromone, the flower produces a chemical that mimics the alarm pheromone of two species of honeybees that are likely to be the wasp’s prey. (I posted on such bee-eating wasps a few days ago.) The paper is short and easy to read; it should be accessible to the non-scientist. And the abstract says it all:

Approximately one-third of the world’s estimated 30,000 orchid species are deceptive and do not reward their pollinators with nectar or pollen. Most of these deceptive orchids imitate the scent of rewarding flowers or potential mates. In this study, we investigated the floral scent involved in pollinator attraction to the rewardless orchid Dendrobium sinense, a species endemic to the Chinese island Hainan that is pollinated by the hornet Vespa bicolor. Via chemical analyses and electrophysiological methods, we demonstrate that the flowers of D. sinense produce (Z)-11-eicosen-1-ol and that the pollinator can smell this compound. This is a major compound in the alarm pheromones of both Asian (Apis cerana) and European (Apis mellifera) honey bees and and is also exploited by the European beewolf (Philanthus triangulum) to locate its prey. This is the first time that (Z)-11-eicosen-1-ol has been identified as a floral volatile. In behavioral experiments, we demonstrate that the floral scent of D. sinense and synthetic (Z)-11-eicosen-1-ol are both attractive to hornets. Because hornets frequently capture honey bees to feed to their larvae, we suggest that the flowers of D. sinense mimic the alarm pheromone of honey bees in order to attract prey-hunting hornets for pollination.

This is the kind of new result that keeps us evolutionists juiced up: you can never predict what kind of bizarre adaptation will crop up in the next issue of a journal.

And if you look at the D. sinense flower, it doesn’t look like a bee or a wasp:

Dendrobium

Figure 3. Dendrobium sinense Flower and Vespa bicolor Forager. D. sinense flower (A) and V. bicolor forager with pollinia stuck onto the thorax (B). (Figure from Brodman et al.)

Apparently the fragrance alone is enough to attract the wasp. And, as predicted from the scent mimicry, the wasp doesn’t try to copulate with the flower; instead, it “pounces” on it, exactly as a wasp pounces on an alarm-pheromone-emitting bee. But that pouncing is enough to stick the pollen sac onto the wasp. As the old saying goes, “Natural selection is cleverer than you are.”

h/t: Matthew Cobb

_______

Brodman, J. R. Twele, W. Francke, L. Yi-Bo, S. Xi-quiang, and M. Ayasse. 2009. Orchid mimics bee alarm pheromone in order to attract hornets for pollination. Current Biol. 19:1368-1472.

*Oh! What a tangled web we weave
When first we practice to deceive!

Walter Scott, Mamion

16 Comments

  1. newenglandbob
    Posted August 26, 2009 at 7:55 am | Permalink

    I wonder what the energy expenditure difference is between flowers that produce nectar or pollen versus those that produce attractive or alarm pheromones versus those that mimic female genitalia.

    But, of course, natural selection is not forward looking, so the energy expenditure difference is not determining factor in any way.

    • Posted August 26, 2009 at 11:25 am | Permalink

      Energy expenditure matters in evolution.

      If there were a point at which an orchid, which previously attracted insects with nectar and scents which indicate food, mutated so that it created a chemical that attracted wasps, and that mutation ended up being successful at causing pollination (along with reduction and/or elimination of nectar production), then the lower-energy cost would certainly factor into the selection of that trait.

      Energy use is a constant pressure in evolution, not simply something that will matter in the future.

      Of course evolution may lock descendants into an energy-inefficient “strategy.”

      Glen Davidson
      http://tinyurl.com/mxaa3p

  2. Posted August 26, 2009 at 9:05 am | Permalink

    The Current Biology article may be easy to read, perhaps. But not accessible to non-scientists without $$$.

    Thanks for your article!

    • whyevolutionistrue
      Posted August 26, 2009 at 9:10 am | Permalink

      I thought this was an open-access journal. At any rate, I’ve posted a new link; my apologies if that doesn’t work.

    • Dave C
      Posted August 26, 2009 at 9:57 am | Permalink

      Adrian, I was able to get a copy of the article through my university. I could email you a pdf if you’d like (Dr. Coyne, please feel free to delete my comment, if this isn’t allowed due to copyright or whatever).

  3. Posted August 26, 2009 at 9:30 am | Permalink

    The Designer works in mysterious ways.

    For what it’s worth, a blurb about this was in either Science or Nature, because I’ve already read about it. Interesting, and worthy of more exposure.

    Glen Davidson
    http://tinyurl.com/mxaa3p

  4. bric
    Posted August 26, 2009 at 9:43 am | Permalink

    I wonder if that’s the strategy of this Vanda orchid, mimicking a bee? Taken in the Princess of Wales Conservatory at Kew

    http://www.flickr.com/photos/bric_uk/3650155703/

  5. gingerbaker
    Posted August 26, 2009 at 10:21 am | Permalink

    Fig. 1. Ophyrys insectifera (fly orchid), which deceives male digger wasps.

    Not to mention what it does to those humans with a Flying Nun fetish. ;D

  6. JefFlyingV
    Posted August 26, 2009 at 10:41 am | Permalink

    It will be interesting to see if the poheroneme can be synthesized and used in traps for the giant wasps that have invaded Europe.

  7. Posted September 9, 2009 at 11:19 pm | Permalink

    just beautiful photos…nature works in mysterious ways..according to ones needs..and needs are always not ugly 🙂

  8. Posted October 10, 2009 at 12:33 am | Permalink

    hahahahah
    thats hilarious – silly sex crazed male wasps lol

  9. poonam
    Posted June 16, 2010 at 9:38 pm | Permalink

    excellent work of nature trying to teach harmony ,coexistance,indispensibility amongst various organisms.Man should learn from these silent creatures instead of fighting amongst themselves.

  10. Joel Schiff
    Posted May 8, 2011 at 3:22 am | Permalink

    Regarding Ophrys pollination, male bees actually preferred the orchids’ floral pheromone odor to the sex pheromone of the female bees in work done by Vereecken & Schiestl, PNAS vol 105, 2008. Could this be an example of Bee porn?

  11. Alfred Shuamate
    Posted February 20, 2012 at 8:53 pm | Permalink

    I don’t see proof of a mindless evolutionary process here but evidence of a very smart God with a really cool sense of humor.I guess we all see what we want to see and then like to claim it as scientific fact.If a mindless process can produce this then with our very developed brains you’d think we could create life from scratch since evolution did it.

  12. Jarad
    Posted March 3, 2013 at 4:02 am | Permalink

    How without eyes does a plant visually mimic a wasps physical form?

    • Notagod
      Posted October 26, 2013 at 10:11 pm | Permalink

      The plant that is more attractive to the pollinator gets pollinated more often thus passing on more of its genotype to future generations. Those future generations might include a mutation that becomes even more attractive to the pollinator and that mutated form will be pollinated more successfully.

      See? It is the wasp that is selecting the plant in this case not the plant selecting the wasp. The plant becomes more “wasp like” because the wasp visits the more “wasp like” plants more often.


2 Trackbacks/Pingbacks

  1. […] Evolution in Action Posted September 21, 2009 Filed under: Environment, Evolution, News, Science | I know I haven’t been blogging lately, but since school has started, I’ve been extremely busy. I’m hoping to post on Mondays to get our intellectual juices flowing. At any rate, check out this image. Awesome stuff.  First of all, guess what that image is? If you thought it was some crazy insect, you’re wrong. It’s actually an orchid.  This orchid has “learned” to mimic bees and wasps. Natural selection has molded the flowers of these orchids (many in the genus Ophyrys) into mimics of the insects that pollinate them.  Thus, males insects, thinking that this orchid is actually a female insect, land on them and tries to copulate with them.  Obviously, it doesn’t work, but during this attempt, the insects’ heads or bodies contact the orchids’ pollen sacs which attaches itself to the insect.  The frustrated insect flies off, but soon tries to copulate with another orchid, which puts the hitchhiking pollen in contact with the new orchid’s stigma. In such a way the bees/wasps serve as “flying penises,” helping the orchids have sex.  You can see the whole article (and more pics) here. […]

  2. […] But mosses, liverworts, and hornworts (a group of plants called bryophytes) brought sex to the land–but how did they adapt to the lack of water for sperm transport? As you probably know, flowering plants often have helpers to do their sexytime work for them. Pollinators (like bees, for example) carry pollen (which contains sperm) to a female flower, eliminating the need for water to carry the sperm. The plant gets away with this because it usually offers something to the pollinator in return: nectar, a place to live, or it might just trick it with sweet sweet smells (like those dirty orchids). […]

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