Weapon performance and contest assessment strategies of the cavitating snaps in snapping shrimp

Animals compete in contests over limited resources. Contestants forfeit once they ascertain that their opponent has greater resource-holding potential (RHP; mutual assessment) or once they reach a threshold of costs (self-assessment). Functional scaling studies of contest behaviour performance can inform how assessment signals, offensive capacity and endurance scale with RHP and thereby elucidate the mechanisms through which each of these assessment types operates. Here, we performed behavioural contest analyses to determine the assessment strategies used in snapping shrimp (Alpheus heterochaelis) contests. Then, we used biomechanical measurements of a common contest behaviour to inform how assessment might operate. We were specifically interested in the snapping behaviour during which snapping shrimp fire imploding cavitation bubbles—hereafter, ‘snaps’—at their opponents. We showed that A. heterochaelis use mutual assessment early in contests. Then, when they fire snaps, they switch to cumulative assessment—a type of self-assessment where contestants endure costs from their own behaviours (e.g. energy) and their opponent's (e.g. injury). Because larger individuals tend to win contests, we then tested how the maximum performance and endurance of snaps scaled with size. We measured the average angular velocity of the snapping dactyl, cavitation bubble duration and pressure of snaps as metrics of performance. We measured 10 snaps per individual (n = 76 individuals). From this series of 10 snaps, we calculated the maximum of each metric as the maximum performance and the attrition of each metric over the course of 10 snaps as a measure of endurance. Maximum performance increased with size, but endurance did not. This suggests that cumulative assessment in snapping shrimp is driven by opponent-imposed costs. Our results are not consistent with self-assessment based on endurance; however, the experiment could not fully replicate the quick succession of snaps fired in real contests. Future experiments should better replicate the rapid firing of snaps to test if endurance matters in a more ecologically relevant context. Our framework of integrating biomechanics and behavioural ecology provides a pathway to identify precise mechanisms of contest assessment and animal behaviour more broadly. Read the free Plain Language Summary for this article on the Journal blog.

Duke Scholars

Author Sheila N Patek Biology