Spot symmetry predicts body condition in spotted salamanders, Ambystoma maculatum

Abstract

Reports of global amphibian declines necessitate a focus on measures of population health. Fluctuating asymmetry (FA) is a potential measure of the developmental stress experienced by individuals in different environments, but few studies have linked FA with measures of individual quality in amphibians, which is an important assumption of FA. The spotted salamander, Ambystoma maculatum, has two rows of yellow spots on its dorsal surface which might represent useful characters in FA analyses and population monitoring, provided they truly reflect the quality of individuals. In this paper we compared left-right asymmetry in spot features (spot number, size and shape) and leg lengths of this species with traditional measures of body size and body condition among museum specimens to address this question. Of all three spot symmetry variables, the simplest (the difference in left-right spot numbers) was the most important. Individuals with asymmetrical spot numbers were also more asymmetrical in hind leg length, evidence that spots are supposed to be symmetrical in this species. Moreover, salamanders with symmetrical numbers of left-right dorsal spots had higher body condition scores than those with asymmetrical spot numbers. Combined, our results indicate that spot number symmetry provides a good index of individual quality. Further, as many proximate factors can influence body condition (such as recent foraging history), FA in characters such as spots or limbs may provide a more stable metric for assessing the developmental health or quality of individuals, which would prove valuable in amphibian conservation programs.