Telomere shortening with age has been documented in many organisms, but few studies have reported telomere length measurements in amphibians, and no information is available for growth after metamorphosis, nor in wild populations. We provide both cross-sectional and longitudinal evidence of net telomere attrition with age in a wild amphibian population of natterjack toads (Epidalea calamita). Based on age-estimation by skeletochronology and qPCR telomere length measurements in the framework of an individual-based monitoring programme, we confirmed telomere attrition in recaptured males. Our results support that toads experience telomere attrition throughout
their ontogeny, and that most attrition occurs during the first 1–2 years.We did not find associations between telomere length and inbreeding or body condition. Our results on telomere length dynamics under natural conditions confirm telomere shortening with age in amphibians and provide quantification of wide telomere length variation within and among age-classes in a wild breeding population.

Data on age estimated by skeletochronology, relative telomere length (telomere/single copy gene GAPDH: T/S ratio) assessed by qPCR, genotype at 16 microsatellite markers, sex and body measures (snout to vent length and body mass) for 211 adult individuals of Epidalea calamita captured in Laguna de Valdemanco (central Spain) between 2010 and 2015. 33 of the individuals have T/S ratio measures obtained in a second capture (recapture) in 2018.

Missing data in the genotypes are coded as '0'.

BC09727 and BC09788 were identified as the same individual after genotyping, although both T/S measures showed different values.