Size-related performance variation in the wood frog (Rana sylvatica) tadpole tactile-stimulated startle response

Abstract

I described the initial response of the Rana sylvatica LeConte, 1825 tadpole to predator contact, that is, the tactile-stimulated startle response (TSR). Because tadpole survival from predation increases with tadpole size and with exposure to chemical predator cues during development, I anticipated that TSR performance would vary accordingly among tadpoles. Startle responses were stimulated in a laboratory setting and filmed using high-speed video. This method allowed analysis of performance at fine spatial and temporal scales. Maximum acceleration performance increased with tadpole length, as did cumulative distance covered after the first 0.016 s of the response. In contrast, the cumulative distance covered during the initial instants of the response did not depend on tadpole size. Exposure to a predator cue (odor of the dragonfly naiad Anax junius (Drury, 1773)) during development had no effect on tadpole morphology. Predator-cue exposure negatively affected cumulative distance traveled after the first 0.072 s of the startle response. I concluded that size-dependent variation in performance of the TSR may partially explain differential survival of tadpoles, but there was no evidence that exposure to this predator cue increased TSR performance.