The Herpetological Journal

Authors: Sinsch, Ulrich

Abstract: A long-standing challenge for amphibian population ecologists is the reliable estimation of age in individuals without known recapture history. The development and widespread application of skeletochronology seems to have solved the issue, although studies evaluating the precision and reliability of age estimates are rare and controversial. Skeletochronology attempts to relate the number of dense hematoxylinophilic narrow growth marks (Lines of Arrested Growth, LAGs) separated by faintly stained broad growth zones in the round bones of Anura and Caudata with age. In this review, I briefly summarise the laboratory procedures to obtain informative histological cross sections, and the interpretation of growth marks becoming visible through staining. I discuss the precision and constraints of skeletochronological age estimation by evaluating evidence derived from individuals with known age. Individuals of up to eight years of age are correctly aged by LAG-counting, whereas the lifespan of older individuals is systematically underestimated, due to the increasing rapprochement of LAGs at the periphery of bones. A case study on the latitudinal and altitudinal variation of demographic life-history traits in natterjack toads illustrates the utility of skeletochronology to assess plasticity of age distributions in response to climate variation. Finally, I provide perspectives for future research to which skeletochronology may contribute valuable information.

Keywords: LIFE HISTORY, AGE AT MATURITY, LONGEVITY, SKELETOCHRONOLOGY, GROWTH PATTERN, LARGE-SCALE VARIATION AMONG AND WITHIN SPECIES