Body size variation of odorous frogs (Odorrana grahami) across altitudinal gradients

We used skeletochronology to determine the ages of 249 (93 females, 108 males and 48 juveniles) odorous frogs (Odorrana grahami) from four locations covering an altitudinal span of 1030-1860 m in Sichuan Province, western China. We found distinct lines of arrested growth (LAGs) from excised toe bone for 242 individuals, and each LAG was assumed to represent one year of age. In disagreement with Bergmann's rule, body size of four O. grahami populations did not change clinally along the 830 m altitudinal gradient. Average adult SVL and age differed significantly among populations in females, but not in males. For both sexes, age did not predict body size. When removing the effects of age, we found significant inter-population differences in body size only for males. Post-metamorphic growth rates in males were highest from the lowest altitude, whereas growth rates of females were highest at high altitudes. Our findings suggest that, apart from age, ecological factors such as trophic resources or predation further shape body size differences between populations and sexes.