Effects of Environmentally Induced Development-Rate Variation on Head and Limb Morphology in the Green Tree Frog, Hyla cinerea

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Abstract
We have little idea to what extent natural variation in the size-independent shape of animals might be owing to environmentally caused variation in whole-body development rate. In this study we experimentally manipulated development rates in both the larval and juvenile stages of the green tree frog, Hyla cinerea, by raising animals at different food levels. We studied the effect of this development-rate variation on that fraction of the variance of head width and of tibiofibula length that remains after removing snout-vent length as a covariate. The development rate of larvae raised at different food levels had no effect on their size-adjusted head width or tibiofibula length at metamorphosis. Similarly, the food-controlled rate at which juveniles developed had no influence on their shape at a larger size. We also raised small metamorphs as juveniles to determine whether, for head width and tibiofibula length, the relation between body part and snout-vent length among metamorphs (static allometry) has the same slope as that relation in growing juveniles (longitudinal allometry). For tibiofibula length, the two allometries are indistinguishable. For head width, the longitudinal allometry may be steeper than the static, but further studies are needed to confirm this result.