Energetic costs, ontogenetic shifts and sexual dimorphism in spider crab decoration

Abstract

Summary 1‘Decorating’ describes behaviours in which animals attach foreign matter to themselves or their external structures. Decorating is widespread, occurring in morphologically and ecologically diverse organisms representing nearly 25% of the major metazoan phyla. 2 Decorating is often limited to juvenile or small life stages. This pattern may suggest that decorating incurs cost-benefit trade-offs limiting its net adaptive value within and across species. Theory predicts that such costs, if present, could strongly influence selection for decorating. 3We investigate the potential costs of carrying decoration and their evolutionary ramifications, using decorator crabs (Brachyura: Majoidea) as a test system. We demonstrate that decoration is energetically costly for the species Oregonia gracilis. 4We experimentally link those costs to sexually dimorphic ontogenetic shifts in O. gracilis claw size and decoration. 5We show that negative correlations between claw size, body size and decorating occur widely in the Majoidea, suggesting that energetic costs have played an important role in majoid evolution. 6This study demonstrates linkages between physiological constraints, sexual selection, and predation risk.