M. J. Adams R. Bruce Bury 1999 <p>Tailed frogs (<i>Ascaphus truei</i>) occur in permanent, cold streams in northwestern North America. Their tadpoles reportedly undergo metamorphosis after 2-4 years. Coastal populations that we examined transformed in 2 yr from the Olympic peninsula in Washington to northern Oregon, but in 1 yr from central Oregon to northern California. One inland site in northern California had a 2-yr period. Age at metamorphosis was consistent over different years. We suggest that total length and developmental stage accurately define cohorts for larval <i>Ascaphus</i>. Hind-leg length indicates whether metamorphs are a separate age class from tadpoles. Age at metamorphosis (1-4 yr) appears to reflect broad differences in climatic conditions. However, at a regional scale, variation is low and suggests a lack of sensitivity to local environmental conditions. This may be due to seasonal constraints on the time when metamorphosis occurs (late summer).</p> application/pdf en Allen Press Variation in age at metamorphosis across a latitudinal gradient for the tailed frog, Ascaphus truei article