Effect of food level and rearing temperature on burst speed and muscle composition of Western Spadefoot Toad (Spea hammondii)

1. Past studies on phenotypic plasticity usually focus on ultimate (evolutionary) issues. More recently, proximate (developmental) factors explaining how plasticity is achieved are starting to be addressed. 2. Here, we examine the importance of resource level and temperature on growth rate and burst swimming speed in tadpoles of Spea hammondii (Western Spadefoot Toad). 3. Food and temperature manipulations alter growth rate via different developmental processes (cell growth and cell recruitment, respectively) and these processes appear to have consequences for swimming performance in tadpoles. 4. Tadpoles reared at warm temperatures were slower swimmers than those reared at cooler temperatures while food level had no effect on size-specific burst speed. Tadpoles reared at warm temperatures also had more fibres in the tail muscle, probably due to an earlier onset of recruitment. Tadpoles reared at higher food levels had larger muscle fibres, but little differences in fibre number compared to those reared at low food levels. 5. These results indicate that growth by adding cells comes at a performance cost not seen when growth is due to increasing cell size. This developmental difference also has implications for how body size manipulations are carried out in behavioural and ecological studies.