Effects of temperature-induced variation in anuran larval growth rate on head width and leg length at metamorphosis

We tested whether temperature-induced variation in the growth rate of Rana cascadae tadpoles caused any variation in head width or leg length at metam orphosis, independent of the effects of temperature on body size. Body-size -adjusted head width appears to be insensitive to even large variations in tadpole growth rate. This result mirrors previous observations on the effec ts of variation in food level and temperature on metric shape in frogs and other ectothermic vertebrates. Leg length, on the other hand, showed a smal l but statistically significant response to the temperature treatment. Fast -growing tadpoles attained slightly longer legs than slowly growing tadpole s at a common metamorphic body size. This example is the first to show that variation in growth rate per se can influence metric shape (i.e., the rate at which individuals reach a common body size determines their shape at th at size). Nevertheless, the induced effects were small, and our results tak en together with those of previous studies suggest that environmentally ind uced variation in growth rate is not a major source of variation in metric shape of skeletal characters in ectothermic vertebrates.