email a friend iconprinter friendly iconDragonfly Mating Game
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Studies show that females constantly hounded by suitors have lower fecundity. So, in the game of evolutionary one-upmanship, females may have evolved different color forms as a response to harassment. According to one hypothesis, a blue female would be hassled less because she looks like a male. Fincke has another explanation, with some startling implications.

"It may be that a female of rarer color doesn't get harassed as much," she posits, "not because she looks like a male but because she's a less familiar form of female and doesn't fit the male's 'search image' for a mate." In recent experiments, Fincke has shown that young males discover what a female looks like by exposure. If they're reared with green females, they choose to mate with green females; if they're reared with blue ones, they'll go for blue. This suggests a revolutionary idea. Male dragonflies learn; their sexual behavior is not hardwired but more flexible, more "intelligent" than anyone ever imagined.

Like most scientists, Fincke follows questions, one leading to another. In her view, sexual conflict may explain another perplexing mystery: the relatively swift evolution of bluet species—18 new species in the past 250,000 years. Speciation is still poorly understood, and the explosion of new species in this genus in particular is a conundrum. "How do you explain the rapid evolution of dozens of different species of blue-and-black damselflies, all of them occupying essentially the same ecological niche?" she asks. Fincke suspects that females with slightly different thoracic plates are favored in evolutionary terms, because male claspers of some species won't fit with them, so not as many males can harass them by taking them in tandem. In short, sexual harassment sparks the evolution of female plates that differ from the usual, which in turn triggers shifts in the shape of male claspers, in an evolutionary tango that gives rise to whole new species and unexpected variety.

The next time a pair of elegant jewelwing damselflies or feisty scarlet darters cavort in the flecked morning sun, consider it: evolution on the wing, in motion, right before your eyes.

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