Altitudinal variation in body size and age structure of the Sauter's frog Rana sauteri in Taiwan

Background: The tendency for organisms to be larger in cooler climates, the so-called Bergmann's rule, has been widely observed in endotherms, but it is debatable in ectothermic anurans. Altitudinal variations in body size, age, and growth rate of the Sauter's frog Rana sauteri were investigated with skeletochronology at six sites along the altitudinal gradients from 330 to 2,320 m in subtropical Taiwan. The aims of this study were to determine whether these life history traits vary with altitude and differ between males and females. Results: The body size of male R. sauteri followed a converse Bergmann's cline; the size decreased with increase in altitude, while no significant altitudinal change was found for females. The size dimorphism was female-biased and became greater at higher altitudes because of the altitudinal decrease in male size. Ages ranged between 1 and 5 years for males and 1 and 6 years for females. There was no significant difference in the age structures between the two sexes, but both sexes had higher average ages at higher-altitude sites. According to von Bertalanffy's model, the growth coefficients decreased with increase in altitude for males but not for females. The annual growth rates were greater for all age classes of females than males, suggesting that growth rate was a major factor underlying body size patterns of both sexes. Conclusions: Growth rate was a major factor underlying body size patterns in both sexes of R. sauteri. It could be affected by not only altitudinal temperature gradient but also sex-biased life history traits and environmental factors.