Sexually selected traits sometimes come with a cost. One risk is that oversized structures intended to attract the ladies may hinder mobility. But in male flower beetles (Dicronocephalus wallichii), the size of their sexually selected horns and forelegs appear to have no bearing on how fast they can scurry across bamboo branches propped at different angles in the lab.
“Our results suggested that no negative relationship exists between relative foreleg length or horn length and sprint speed,” the authors write in their paper, published this month (November 18) in Ethology. In fact, the researchers found that beetles with longer horns could actually run faster on horizontal branches. “Males with longer horns probably have more energy and/or invest more heavily in appendage musculature,” they speculate. “As is known in other animals, male horns of D. wallichii may act as honest indicators of body condition.”
W. Kojima, C.-P. Lin, “Sprint speed is not reduced by exaggerated male weapons in a flower beetle Dicronocephalus wallichii,” Ethology, doi:10.1111/eth.12824, 2018.