Abstract
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. 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. 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.
Highlights
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
At the 2,100- and 2,320- sites, the breeding season occurred from May to June, but tadpoles were observed in the water all year round
Breeding activity period decreased from 11 weeks at the low-altitude sites to 3 weeks at the high-altitude sites (Table 1)
Summary
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. The aims of this study were to determine whether these life history traits vary with altitude and differ between males and females. Many endothermic vertebrates with larger body sizes live in cold environments, the so-called Bergmann’s rule. It infers that larger body size would have better ability of conserving heat in cold climates which characterize high-latitude and high-altitude regions (Macholán et al 2008). Up to now, it still remains controversial whether Bergmann’s rule is applicable to body sizes of ectothermic vertebrates like amphibians (Ashton 2002; Adams and Church 2008). The tendency of body size variation in male may differ from that in female within species in the frogs (Zhang et al 2012; Liao et al 2013). Altitudes and latitudes may cause a similar temperature effect on amphibians (Morrison and Hero 2003; Sinsch et al 2010), so it would be necessary to reduce the latitudinal effect in investigating altitudinal effect on body size in amphibians
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