How the Flower Learned to Trick the Insect … in Bed

October 10, 2012 § Leave a comment

Flowers might look all pretty and innocent to you and I, but deep down, they’re exploitative little bastards and masters of deceit.

Consider this: at the very least, most flowers will use their nectars and colors to bribe birds and insects into handling their pollinating needs, and more than a few don’t stop there. Serapias orchids and certain irises, for instance, often use their petals to offer deep tunnels and dark colors for their foot soldier bees to rest in overnight or during bad weather—shelter mimicking, it’s called. Craftier yet, Ophrys orchids famously imitate insect shapes (usually bees) and scents to lure lonely male bees onto their petals for a round of faux-sex for the bee and real pollination for the flower.

Now traditionally, three basic premises have shaped researchers’ concept of floral deception. First, only orchids engage in sexual deception. Second, sexual deception and shelter mimicking strategies are mutually exclusive among genera: an iris or a Serapias orchid might offer a bee a place to nap, but would never try to tempt it with its wiles, and vice versa in Ophrys orchids. Third, once a flower species has specialized itself to the point of sexual deceit — a strategy so refined it targets only one gender of a single species of a given pollinator — there’s no real going back. Evolution’s not a two-way street.

But according to a new paper in The Proceedings of the Royal Society B, there’s a catch. Ready? The catch is: all three of those premises are wrong.

To get the full gist of this, you want to go back a few years or so ago, when the study’s lead author Nicolas Vereecken of the Free University of Brussels, Belgium, was investigating the odors of the sexually sneaky Ophrys orchids and wondering how in the heck something like this evolved in the first place. Hoping to find evidence for some sort of evolutionary intermediary, he took to the field and started looking everywhere from the Caucasus and Albania, to the island of Sardinia and southern France.

That’s when he found a Serapias orchid that didn’t look like any of its peers. It wasn’t dark red, it wasn’t a tunnel, and it clearly wasn’t hosting bees overnight as a shelter. In fact, it seemed to be drawing just the males of a single species of bee, and only during the hot hours of the day—almost like… yes: chemical analysis proved it: Serapias lingua was exuding female bee chemicals. Sexual trickery. The first time the phenomenon had ever been found outside of the Ophrys in that part of the world, and the first time it had ever been found in a group that usually uses shelter mimicry.

Things got weirder after that: he discovered an OphrysO. helenae—in northern Greece that turned out to be hosting bees instead of seducing them, and after that, he tracked down the aptly named Iris paradoxa in Azerbaijan that turned out also to be also using sexual deception (that’s the video at top). That was another first: the first time sexual deception had been found in an iris. (It was also the second time only sexual deception had ever been found outside of orchids at all, and in that case the African daisy has been using it as a more general way to amplify its pollination work without zeroing in on only the single males of a single species.)

This paper now is the culmination of five years—four in the field—spent on those three flowers and their pollinators, digging into their behavior, colors, chemical scents, and especially their genetic ancestry. Besides confirming what Vereecken had seen in the field, it gives a hint into how all this happened. None of these changes were outrageously dramatic—only a few specific chemical tweaks in scent, color, and shape were really required for the flowers to jump from tact to tact. Vereecken thinks that’s the clue he needed to understand how the property evolve. “Shelter mimicry could provide pre-adaptations, narrowing down the spectrum of pollinators towards the exclusive use of males of only one species.” Now that he has a foothold, he and his colleagues can use future studies to do more digging.

But more importantly, these changes also didn’t obey Cope’s century-old rule. “When we started looking at the evolutionary transitions, we found evolution went from shelter mimicry to sexual deception in irises and Serapias,” says Vereecken. “And the other way around in Ophrys.”  In other words: Cope’s wrong. Specialization does go both way sometimes, and we’re living in a world where even a flower can have an evolutionary change of heart.

Vereecken NJ et al. Pre-adaptations and the evolution of pollination by sexual deception: Cope’s rule of specialization revisited. (2012) Proc R Soc B. doi:10.1098/rspb.2012.1804. Video also courtesy of Vereecken et al.

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