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By Root 319 0

obliging characteristics of dung beetles from the perspective of the scientists who study them is the ease of obtaining the raw material, so to speak. Leigh and Paco simply turn up at a local dairy farm and ask the farmer's permission to rummage around in the droppings left in the pasture, permission that is virtually always granted, albeit not without some quizzical looks. It is always difficult under such circumstances to decide exactly how much one should explain about the reason behind the request, striking a delicate balance between Too Much Information ("Here, let me tell you all about the evolution of male genitalia in beetles!") and sinister-seeming reticence ("Oh, nothing special, really. I'm doing a project on, um, sex."). From long experience, Leigh has figured out how to make such requests without alarming the farmers, and he and Paco duly brought back about a thousand beetles to his laboratory.

Leigh and Paco then performed what is called experimental evolution, by altering the environment of the beetles to see if the hypothesized selection pressure, namely, the risk of sperm competition, had the predicted effect on the beetles' testes size. It is really just artificial selection, the same process used to obtain do mesticated animals or crop plants with desired characteristics. The researchers set up populations of the beetles under different circumstances: monogamy, with a set of randomly chosen males and females paired so that there was no risk of competition among rival males; and multiple mating, with buckets containing ten individuals of each sex so that the males could jockey for access to the females. The offspring from each of the experimental treatments were then placed in the same situation as their parents, and so forth for twenty-one generations, which took about four and a half years, since a dung beetle can get from egg to adult in about eight weeks.

At the end of the experiment, the males in the monogamous treatment had smaller testes than those from the lines in which sexual competition had been allowed to continue. This was clearly a genetic response, not simply a "use it or lose it" effect of the treatment, because the beetles were measured just after they reached sexual maturity but before they had time to mate. Leigh and Paco could also use genetic analysis to determine exactly which males fathered the most offspring, and they found that when given the opportunity to compete, males from the monogamy lines were not as good at fertilizing the females' eggs as males whose ancestors had been allowed to mate in groups. They concluded that sperm competition drives the evolution of testes size and sperm viability in these beetles, just as the theory predicts.

A Funny Thing Happened on the Way to the Egg

AS I mentioned above, many of the early researchers studying sperm competition were men, and without delving too deeply into their motivations, it is safe to say that most of them did not consider the female's side of the equation. Once Eberhard and a few others got things started, however, it became clear that female insects did not simply lie around passively waiting for the sperm to duke it out inside their bodies. One of the best examples of cryptic female choice is found in the humble flour beetle, the same tiny pest that infests the canisters of flour and other grain products in your kitchen. Lurking inside these miniature creatures is a hotbed of reproductive intrigue.

Tatyana Fedina, now at the University of Michigan, performed some extremely clever—if grisly—experiments on the beetles when she was a graduate student at Tufts University to see just how much say the females had over the fate of sperm. Flour beetle males pass sperm to females in a tube that turns inside out once it is in the female's body. The beetles mate with multiple partners, and some males father more offspring than others. But who controls paternity? Is it the males, via sperm competition, or the females, via selective use of sperm?

Fedina took advantage of the rather oblivious nature of male flour beetles when