Novel Allometric Estimators Improve Estimation Accuracy of Body Surface Area, Volume, and Surface Area-to-Volume Ratio in Lungless Salamanders (urodela: Plethodontidae)

Abstract Body surface area and volume are both physiologically important traits in amphibians, as their ratio constrains transport rates for water and respiratory gases across the skin. This is especially true in the lungless salamanders (Urodela: Plethodontidae), whose lungless morphology restricts nearly all gas and water transport to the body surface. Due to methodological difficulties of measuring surface area and volume, estimation techniques are the most convenient way to produce usable phenotype scores. To this end, we used high-resolution computerized tomography (CT) scans of three plethodontid species varying in body size and shape to produce allometric regression models to estimate body surface area (SA), volume, and surface area-to-volume ratio (SA:V). We compared our model estimates to empirical measurements and established estimation methods employed in the Plethodontidae using linear models and Deming regressions. We found our model estimates are both accurate and generalizable across temperate plethodontid species. This method significantly improves SA estimation accuracy when compared to published allometric models. Our models are also significantly more accurate than SA or volume estimates following geometric measurements, although SA:V estimates are comparable between these techniques for most body sizes. We discuss the relative utility of different estimation methods for future research questions.