Sánchez-Montes,
G.,
Rotger, A., Caballero-Díaz, C., Tavecchia, G., Gutiérrez-Rodríguez, J. and
Martínez-Solano, Í. 2026. The Wonder Years: A
Demographic Approach to Revisit the Age-at-Size Conundrum in
Amphibians. Integrative Zoology. https://doi.org/10.1111/1749-4877.70086
In a shell: This study shows that long-term capture–mark–recapture data combined with growth models can reliably estimate age from body size in amphibians, overcoming limitations of traditional methods. By applying this approach across multiple species, we improved understanding of age structure, maturity timing, and recruitment patterns, highlighting its value for amphibian conservation and demographic research.
Abstract: Characterizing age–structure patterns in amphibian populations is
crucial to unravel the drivers of their demographic dynamics and
implement biologically informed conservation management. Consequently,
accurately assessing the age of individuals in wild populations is of
utmost importance in the face of the current amphibian crisis. However,
age estimation in amphibians has so far remained elusive due to the
difficulty of lifetime tracking, especially during the terrestrial
juvenile stage, and to the uncertainty associated with alternative
methods like skeletochronology.

Here, we illustrate the usefulness of
long-term monitoring programs based on capture–mark–recapture to address
age estimation from body size data. Specifically, we combined repeated
body size measurements of marked individuals of unknown age throughout
their adult life with growth records of individuals marked as
postmetamorphic juveniles and recaptured years later as sexually mature
adults, focusing on 10 amphibian species in central Spain. Growth models
fitted to mark–recapture data provided robust estimates of size-at-age,
supported by data on individuals of known age for five of the study
species. For three additional species, known age records disproved
mark–recapture models, but rendered enough data to build alternative
growth models. The inferred consensus size estimates allowed discerning
first- and second-year age classes in some species, contributing to
assess the age at maturity of individuals and population-specific
patterns of recruitment. Consequently, our demographic approach provided
multi-evidence information to address age-at-size estimation in
amphibians, thus demonstrating the value of long-term mark–recapture
programs to fill pervasive gaps in our knowledge about amphibian
demographic dynamics.