RENEE MONTAGNE, host:
A basic question for the survival of any species, including humans, is how does a boy get the girl? Scientists know that competition among males is a big part of the answer.
Still, as NPRs Joe Palca reports, even when the boy gets the girl, the competition doesnt end.
JOE PALCA: In the animal kingdom, males are always looking for a leg up against the competition.
Ms. HEIDI FISHER (Harvard University): Large antlers and colorations that allow males to obtain access to female.
PALCA: Thats Heidi Fisher, a biologist at Harvard University. Things like big antlers and bright colors help male animals get a females attention. What Fisher is interested in is what happens next.
Ms. FISHER: This is the point at which the animals have already mated and theres still male-male competition.
PALCA: Its just a different kind of competition. Heres what Fisher means. She studies mice. From a male mouses point of view, after he has mated, the competition is over. It doesnt matter which of his sperm fertilizes the females egg. But...
Ms. FISHER: From the sperms perspective, of course it wants to be the sperm within the whole sample to fertilize the egg.
PALCA: So now its the sperm that compete. One strategy for getting to the egg might be called every man for himself. Each sperm would go it alone and hope for the best. But Fisher and others have shown that a clump of sperms swimming together move faster than a single sperm swimming alone.
Ms. FISHER: Its almost as if, if you dont cooperate, you'll be left behind. Because only the cells that are cooperating are going to be able to reach the egg with a decent speed to have a chance of fertilizing the egg.
PALCA: You still have to compete with other sperm in the clump when you reach the egg. But hey, at least you got there first. In her latest research published in this weeks Nature magazine, Fisher adds an interesting twist to the story. Female deer mice, it turns out, are promiscuous. They mate with several males when they go into heat. Fisher wondered whether the sperm would still take the approach of all-for-one and one-for-all, or whether sperm from one mouse would compete with sperm from another. So she took sperm from one male mouse and dyed it red.
Ms. FISHER: And then sperm from another male, and we dyed it green.
PALCA: Then she mixed the two sperm samples together, put them in a petri dish, and watched what happened.
Ms. FISHER: And what we found more often than not is that red sperm tend to clump more so together and green sperm tend to clump more so together.
PALCA: Or to put it more colloquially, sperm of a feather flock together. Fisher doesnt know how sperm know who to buddy up with and who to snub. All she knows is that they do, and presumably its all part of that drive to be the one to pass your genes on to the next generation.
Joe Palca, NPR News, Washington.