Meeting Abstract

P1-45   -   Scaling of offensive capacity and endurance in a cavitation-based animal weapon Dinh, JP*; Patek, SN; Duke University; Duke University jpd29@duke.edu http://www.jasonpdinh.com

Contests are agonistic interactions over limited resources. Contestants with greater fighting ability, or resource holding potential (RHP), typically win contests. In mutual assessment, contestants assess their opponent’s relative RHP and forfeit when they ascertain that their opponent is stronger than they are. In self assessment, contestants do not assess their opponent’s fighting ability; instead, they accrue costs, either self-imposed exclusively (pure self assessment) or self-imposed and imposed by the opponent (cumulative assessment) until they reach a cost threshold. Although assessment strategies are well-studied, the mechanisms underlying assessment often remain black-boxed. Here, we identify physical and physiological mechanisms that could underlie assessment in the snapping shrimp, Alpheus heterochaelis. In particular, we were interested in the cavitation bubbles (hereafter, “snaps”) fired from their enlarged and ultrafast claws. We found that snapping shrimp begin contests using mutual assessment, but in escalated contests when snaps are fired, they switch to cumulative assessment. We collected high speed video with synchronous audio (n = 188 individuals, 10 snaps per individual) to assess how maximal performance and endurance of snaps scaled with size. Larger individuals produced longer lasting cavitation bubbles and greater pressures, suggesting that offensive capacity scales positively with size. To our surprise, however, larger individuals had lower endurance than smaller individuals: as more snaps were produced, bubble duration and pressure decreased, and this effect was strongest for large individuals. We conclude that in the snapping shrimp, cumulative assessment is likely driven by offensive capacity and not endurance. More broadly, there may be trade-offs in weapon performance such that larger weapons impose greater costs, but they are costly to repeatedly deploy.