Reduced burst speed is a cost of rapid growth in anuran tadpoles: problems of autocorrelation and inferences about growth rates

1. It is becoming clear that individual growth rates are optimized to suit local conditions rather than maximized to be as fast as possible. To understand this adaptive variation in growth rates, we need to understand the costs of rapid growth. 2. Recent work in teleost fish suggests that a trade-off between growth rate and critical swimming speed may be common. The current study demonstrates that the trade-off also occurs in anuran tadpoles with regard to burst speed. 3. Individual growth rate and burst speed were compared in Bufo americanus and Scaphiopus hamondi , representatives of two distantly related anuran families. Path analysis showed that growth rate is negatively correlated with burst speed. Because the trade-off between growth rate and swimming speed occurs in two such distantly related anuran species as well as teleosts, it may be general for all vertebrates. 4. However, identifying costs of rapid growth is complicated by the indirect effects of growth rate on body size which will also often correlate with performance factors. Distinguishing between direct effects of growth rate and indirect effects through body size is difficult because the two necessarily result in collinearity. A randomization test shows just how severe this problem can be.