Seasonal variation of the relationship between body condition and fluctuating asymmetry in two sympatric ranid frogs

Abstract

Fluctuating asymmetry (FA) in organisms is an indicator of disturbances during development. This indicator has been associated with multiple causes, such as presence of metals, and organic and inorganic pollutants. However, the effect of FA on individual traits has been little explored. In this study, we examine the presence of FA in some morphological characters in two sympatric species of ranid frogs, Lithobates spectabilis and Lithobates zweifeli, predicting that L. zweifeli would exhibit more characters with FA and higher levels of FA. We also evaluated whether body condition in the two species differ between seasons and whether body condition is associated with FA of limb characters in two seasons. We predicted that this association would be more pronounced in the dry season. We found FA in tympanum and limb characters in both species, but L. zweifeli exhibited FA in one character more than L. spectabilis, as well as higher levels of FA in the horizontal length of the tympanum. Additionally, the characters exhibiting FA only in L. zweifeli are presumed to be more relevant for locomotor performance, fitness and survival than those exhibiting FA only in L. spectabilis. We did not find differences in body condition between seasons in either species, but we found a negative correlation between body condition and FA of the humerus in L. zweifeli. However, this correlation was detected in the rainy but not in the dry season, which could be related to depletion of energetic reserves associated with reproductive investment. This study highlights the importance of evaluating sensitivity of sympatric species through analyses of FA and its effects on individual traits, as well as the analysis of these effects in seasons with different environmental conditions. Keywords: Atoyac basin, limb asymmetry, Lithobates, Mexico, tympanum asymmetry