Nature finds a way

While the seemingly perfect and beautiful complexity that results from evolution is amazing, I find that one of the most fascinating things about evolution is how natural selection favors what works best, not what is perfect. Zuk demonstrates this by describing a curious change in cricket morphology and behavior as a result of rapid evolution.

She studies the relationship between parasitoid flies and their cricket hosts. When the flies locate calling male crickets by the frequency of their calls, they lay eggs inside the crickets' bodies, which then hatch and devour the cricket from the inside out. Nature finds a way, but sometimes its a pretty gruesome way... This puts male crickets in a conundrum: males must call to attract females, which is necessary for reproduction; but calling also attracts parasitoid flies, which is detrimental to survival. What's a guy to do?

What she found is incredible. In a short number of years, many (but not all) male crickets lost the morphological feature which allowed them to call, thus preventing parasitism. This finding not only demonstrates that evolution can occur rapidly, but also presents a new interesting question: How do male crickets that don't call continue to reproduce if females can no longer find them (which they do by following the sounds of the male cricket's mating call)? Zuk's answer is one of my favorite explanations in the book because it demonstrates the maxim that nature finds a way:

"The answer is turning out to be complicated, with the females apparently willing to mate with the silent males as long as the males are near one of the few remaining callers"

Woah. So these silent males have minimized the costs of calling (parasitism) while mooching the benefits of calling from their noisy neighbors. They might not enjoy as much fitness as they would if there were no parasitoid flies at all, but some fitness is better than no fitness, and evolution isn't perfect. It just finds a way.

Also, the finding that silent males mooch off of the calling males raises a series of new questions: Why didn't this strategy evolve in the first place? Even in the absence of parasites, calling probably puts males at a higher risk of predation from other predators, so it seems that, for at least a portion of the population, silently waiting near a calling male might yield more fitness than actually calling. The appropriate strategy might then be maintained by frequency-dependence, such that being a caller or a mooch is dependent on how common the one is to the other in the population.

The fact that this behavior didn't evolve in the past suggests that there is more benefit to calling than allowing a female to find you. It may be that females are choosing males bast on the quality of their calls, not just on their ability to find them. If this is the case, how are females assessing the quality of silent males? Are they just getting fooled?

I love how an answer to a question leads to even more questions. Nature may always find a way, but biologists can't always explain it. But we try, and often do.