Meeting Abstract

7.3  Wednesday, Jan. 4  It’s costly to be honest: the metabolic expense of maintaining a reliable signal of strength for crustaceans BYWATER, C L*; WHITE, C; WILSON, R S; The University of Queensland; The University of Queensland; The University of Queensland c.bywater@uq.edu.au

Handicap costs are predicted to be one of the primary mechanisms for the maintenance of reliable signals that are used during intra-specific communication. However, separating the costs required to unambiguously communicate a message to a receiver (efficacy costs) from the actual costs of producing a reliable signal (handicap costs) is empirically very difficult. Displays of weaponry by crustaceans offer an opportunity to measure the costs directly associated with signal reliability. A unique feature of crustacean morphology is that their claw muscles, which influence their fighting capacity, are concealed beneath an exoskeleton. Thus, it is impossible for competitors to accurately assess the strength of their opponents without physical contact, which is potentially very costly. This feature allows us to separate the signal magnitude (claw size) from its reliability (strength). We quantified the metabolic costs of maintaining claw muscle for original- and regenerated-clawed fiddler crabs (Uca vomeris) and male and female slender crayfish (Cherax dispar). We found that the total metabolic costs of claw muscle for fiddler crabs with weak regenerated-claws represented 12% of their total metabolic rate, which was half of that for crabs with the stronger original-claws. Thus, male fiddler crabs with the weaker regenerated-claws save around 10% of their total resting metabolic demands by producing a claw with less muscle. Although male and female crayfish both had similar overall costs for claw muscle (approx. 30% of resting metabolic rate), claw muscle from male crayfish exhibited half the metabolic rate per gram of tissue than females. Thus, from our studies of crustacean claws, we found that the metabolic costs of maintaining claw muscle could be a powerful incentive for producing weak claws.