Males compete for females' attention. It's a pattern seen throughout the animal kingdom. But new research shows that kind of male-male competition persists even after animals have mated.
Biologist Heidi Fisher of Harvard University sees that competition in deer mice. As it turns out, female deer mice are promiscuous. They will frequently have multiple mates when they go into heat.
Fisher knew from earlier research that sperm that cooperate by clumping together have a better chance of reaching the egg than sperm that go it alone.
Fisher wondered whether sperm from two different male mice would cooperate indiscriminately or tend to clump with sperm from the same mouse.
So she took sperm from one male deer mouse, and dyed it red, and sperm from another male and dyed it green.
Then she mixed the two sperm samples together, put them in a petri dish ... and watched what happened.
"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," says Fisher.
Or to put it more colloquially, sperm of a feather flock together.
Fisher doesn't know how sperm know whom to buddy up to and whom to snub. All she knows is that they do, and presumably it's all part of that drive to be the one to pass your genes on to the next generation.
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