Tadpole density changes the relationship of red-eyed treefrog morphology and jumping performance [poster]

As organisms develop, increased body size is often accompanied by shape changes that alter the morphology–performance relationship. Animals with different growth histories may also have different shapes at similar body sizes. To investigate how larval growth history affects the morphology–performance relationship, we raised red-eyed treefrog tadpoles (Agalychnis callidryas) at three densities (5, 25 and 50 tadpoles per 400 L tank) and measured jump distance during metamorphosis. We predicted that tadpoles grown at low density would metamorphose into larger frogs with relatively longer legs than those grown at higher densities. We also expected low density frogs to jump further – both absolutely, because of their larger body size and relative to their size if they had longer legs. Frogs from low density had longer snout-vent lengths (SVL) than those from medium and high densities and longer tibiafibula lengths and greater masses relative to their SVL. Jump distance was strongly correlated with tibiafibula length; however, there was a significant density*tibiafibula interaction. While longer tibiafibulas in high and medium density frogs were correlated with longer jump distances, there was no such correlation in the frogs from low density tanks. We interpret these results as a consequence of the greater relative mass of the frogs from low density tanks. The relatively long legs of these frogs may not fully compensate for their disproportionately higher mass. This study demonstrates that different larval densities can change not only red-eyed treefrog morphology, but also the morphology–performance relationship. It suggests a trade-off where low larval density can increase body size and presumably fat reserves, but the latter may decrease jumping performance