Honesty Is Costly in a Deceptive System: Locomotor Costs of Producing Large and Strong Weapons for the Crayfish Cherax destructor.

Abstract

AbstractTheory predicts that signals of strength should reliably reflect an individual's fighting ability, with the costs of producing and/or displaying high-quality signals maintaining their reliability. Crustaceans offer a unique system to explore these costs because signal (chela) size and reliability (strength relative to size) can be decoupled-chela muscles are concealed beneath an exoskeleton, allowing some individuals to display large but weak chelae. In this study, we quantified the locomotor costs associated with weapon size and reliability in males and females of the crayfish Cherax destructor using both correlative analyses and experimental manipulations. We measured chela size, strength, and swimming performance of crayfish when intact, after an initial chela removal treatment (control, one, or two), and again after removal of the remaining chela/chelae. We predicted that larger chelae would reduce swimming performance because of added mass and drag and that relatively stronger individuals (greater reliability) would swim slower because of energetic investment in muscle. We found that males and females with larger chelae swam more slowly and that speed increased following the removal of one (11.6%) and two (14.6%) chelae. Individuals with relatively larger chelae showed a greater increase in speed after both chelae were removed. Crayfish with relatively stronger chelae swam more slowly, but this pattern did not hold after chela removal. Our study is the first to demonstrate the independent costs of both signal size and their reliability. While individuals must bear the costs of signaling large weapons, the costs of their reliability may also incentivize the use of unreliable weapons.