Effects of Season, Gravidity, and Streamflow on Body Condition from Tail Width in Two Federally Listed Salamanders, Eurycea sosorum and E. tonkawae

In population studies, individual physiological metrics can reveal important aspects of ecology and act as indicators of overall population health. Body condition is frequently used as a metric of physiological status and commonly quantified as some function of mass relative to structural size. In this study, we examined the natural variation in body condition of two central Texas spelerpines (Eurycea sosorum and E. tonkawae: Plethodontidae) to understand their nutritional status as a function of environmental variability and reproductive condition. Rather than using a mass-based metric to generate a body condition index (BCI), we used residuals from a linear regression of tail width vs. body length measured from subject photographs taken from the dorsal perspective. Overall, mean BCI for both species was lowest in the winter and generally higher in spring and summer. Streamflow had a small positive effect on E. tonkawae BCI and a negative effect on E. sosorum. BCI. Gravid individuals for both species had lower BCI during autumn and winter (when the proportion of gravid individuals was the greatest) than nongravid individuals. By contrast, the few gravid E. sosorum we observed in summer had higher BCI than nongravid individuals. Our results provide important baseline information on the ecology of these federally protected salamanders and demonstrate the utility of a BCI based on width instead of mass.