Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [50]
As the name suggests, dung flies use cow or other animal droppings as a nursery in which to raise their young, and during summer, the female flies of one well-studied species, the yellow dung fly, seek out the freshly produced pats in meadows all over northern Europe. Once they arrive, they are immediately pounced upon by the males, which have been performing surveillance flights on the dung. As Leigh puts it in his book Sperm Competition and Its Evolutionary Consequences in the Insects, "On capturing a female, males will begin to copulate immediately. Struggles for the possession of females are intense. Searching males will pounce upon copulating pairs, with the result that large balls of golden flies can be seen tumbling about the dung surface while the object of their desire is pushed and pulled in all directions; sometimes females are drowned in the dung surface or otherwise injured to the extent that they can no longer fly. When the density of males on and around pats is high, a male capturing an incoming female will carry her in flight to the surrounding grass to copulate before returning her to the dung to lay her eggs. During oviposition [egg-laying] the male remains mounted upon the female and pairs separate only after a clutch of eggs is laid."
Aside from making it clear that my friend is a man who truly loves his subjects of study, this lyrical description points out several crucial aspects of dung fly romance, and hints at why thinking outside the fertilization box will be illuminating. First, why would the males bother to take the females away from the melee before mating with them? Second, why bother staying while the female lays her eggs, which occurs after the male has deposited his sperm? And finally, why should mating take over half an hour, a seemingly excessively long time for the simple act of sperm meeting egg?
The first person to try to answer these questions was Geoff Parker, who in addition to being an evolutionary theorist is something of a dung fly devotee himself. He and others established that the males' behavior helps their sperm to compete with the sperm of any other males with whom the female mates. The last male to mate with a female typically fertilizes most of her eggs, particularly if he can stay engaged with her for at least 30 minutes and displace the sperm of her previous mates. This means that time spent hanging around the female or sequestering her from other males is time well spent, even if the male isn't actively engaged in transferring sperm.
After Parker's pioneering work, biologists threw themselves into an examination of the fate of sperm after mating, and hence into a scrutiny of the male organs themselves. There is nothing like a view of the genitalia of insects to convince you that the male equipment in human beings is rather dull and pedestrian in its appearance. In contrast, male damselflies have penis equivalents that boast a terrifying array of spikes, scoops, and hooks. The humble chicken flea has genitals bristling with strange knobs, kinks, and coils that Eberhard calls "one of the marvels of organic engineering," citing its "morphological exuberance." We never see these organs because the insects themselves are so small and their private parts are often held inside the body until they are needed, but similar well-cloaked monstrosities lurk in most insects.
What these elaborate structures do, more similar to the function of antlers on elk or the curving horns of bighorn sheep than to the genitals of many other animals,