The species appear to do this by either better protecting their testes or producing horns far from their testes—such as on their heads—where the organs are least likely to compete for the same resources.
"The testes truly are primary, and these beetles found a way to protect them," Emlen said.
"In species that don't have protected testes development, you don't get the really big horns."
Armin Moczek is a biologist at Indiana University in Bloomington who is an expert on the evolution of beetle horns. He was not involved in the study.
He said he has "absolutely no doubt trade-offs will turn out to be one of the major ingredients in determining the path that evolution takes."
He adds, however, that more data is required before drawing firm conclusions regarding when, where, and how such trade-offs influence evolutionary trajectories.
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