Age and body size of Salamandrella keyserlingii (Caudata: Hynobiidae): a difference in altitudes, latitudes, and temperatures

The debate surrounding Bergmann's rule, in which the body size of animals is predicted to be larger in cooler environments, is still open concerning ectotherms. Our goal was to test this rule in the broadest ranging amphibian species Salamandrella keyserlingii. We determined age and body size in a cooler region (Darhadyn, Mongolia: mean yearly air temperature = -8.31 A degrees C) using skeletochronology, and compared their differences in altitude, latitude, and temperature with those of a warmer area (Kushiro, Japan: 7.98 A degrees C). In Darhadyn, both sexes reached sexual maturity at 5-6 years of age (growth coefficient: male = 0.585, female = 0.266), 2-3 years later than those in Kushiro (male = 1.341, female = 1.129). Mean body size was smaller in Darhadyn (53.08 mm) than in Kushiro (57.63 mm) for males despite their constant metamorphic size around 30 mm. We also analyzed data available from published studies for 27 populations within the geographic range of this species from 43 to 69A degrees N across a 2,900-km long latitudinal gradient. The analysis indicated an intraspecific tendency to decrease body size with increased latitude from 43 to 57A degrees N, to increase size from 57 to 69A degrees N, and to decrease body size with decreased temperature from 8 to -7 A degrees C and increase size from -7 to -15 A degrees C. This pattern does not follow the intraspecific extension of Bergmann's rule and may follow the converse of Terentjev's optimum rule-a rule formulated to be an inverted-U shaped curve between increased latitude (or decreased temperature) and increased body size.