State-of-the-Art Age Determination Methods for Amphibians and Reptiles

In this work, we provide an overview of the age determination methods of amphibians and reptiles, critically evaluating their methodological principles, utility (including range of applicability), as well as experimental and biological limitations. Potentially, the most reliable age estimation method is the capture-mark-recapture (CMR) technique, allowing a precise chronological age estimation of wild individuals. However, this is a time-consuming method and is not always applicable. Among the indirect methods of age estimation, skeletochronology is one of the most reliable techniques and has been successfully applied in numerous species of amphibians and reptiles. Skeletochronology is based on the interpretation of the growth marks (especially lines of arrested growth or LAGs) that form in hard-mineralized tissues. Other indirect methods such as the counting of growth marks on epidermal scutes, dermal scales, and claw sections have shown to be less reliable and/or have a more limited range of applicability. Recently, the estimation of chronological age using molecular methods has acquired new perspectives from different approaches. Among them, measurements of telomere length and DNA methylation represent promising and minimally invasive methods, but their effective use requires further refinement and testing on a larger number of species.