Form, function, and fitness: pathways to survival.

Two hypotheses have been considered in the literature regarding how anuran morphology reduces predation risk: by (1) improving escape swimming performance, or (2) using the tail as a lure to draw predator strikes away from the body of the tadpole. We investigated these hypotheses using a modification of the morphology, performance, and fitness path analysis of Arnold (1983, Am. Zool. 23:347-361). Indirect effects of morphology on fitness, as mediated by burst swimming speed, as well as direct paths from morphology to survival with dragonfly larvae were included in the path model. Tadpole morphology did affect burst swimming speed, however, burst swimming speed did not influence survival. Fast tadpoles were larger overall, had long tails, deep tail muscles, and proportionally small bodies. In addition, a shape trait similar to published descriptions of the tail lure morphology had a direct relationship with survival. Thus, only the tail lure effect was supported. This study documents the utility of analyzing multiple trait effects and demonstrates that including direct paths between traits and fitness in the morphology, performance, and fitness path model allows evaluation of alternative hypothesis of selection.