Oct. 17, 2006 —Beetles with the biggest horns have the smallest testes, say scientists who show that in evolutionary terms you can't have it all.
They say their finding is clear evidence of an evolutionary trade-off between the ability to fight off sexual competitors and reproductive potency.
Or put simply, the ability to find a mate and the ability to fertilize her.
Leigh Simmons of the University of Western Australia and Douglas Emlen of the University of Montana published their findings online Tuesday in the Proceedings of the National Academy of Sciences.
The researchers looked at beetles of the genus Onthophagus, dung beetles known for the size and variety of their horns.
"What we did was test a fundamental assumption underlying evolution ... that males face a trade-off between competing for access to lots of females and investment in gaining fertilization with those females," Simmons said.
"They need to have big horns to win fights and get females and they need to have big testes in order to win in sperm competition.
"But they can't do both, so species which invest very heavily in their horns tend to invest less in their testes."
