Application of skeletochronology to a population of Pelobates cultripes (Anura: Pelobatidae) from Portugal

We applied skeletochronology to a sample of Iberian spadefoot toads, Pelobates cultripes, from Serra da Arrica, an agro-forestal area in south-central Portugal marked by cool, rainy winters and hot, dry summers. These environmental conditions allow winter activities but constrain toads to a 12-16 week aestivation period. Lines of arrested growth (LAGs) in phalanges were easily readable albeit, unexpectedly, of varying distinctiveness. Double LAGs were scarce as predicted from the observation of a simple seasonal activity cycle. Limited endosteal resorption did not affect any LAG. Age of adult females ranged from 2-7 yr (N = 40) and that of adult males from 2-8 yr (N = 20). Mean adult snout-vent length (males, 52.8 mm; females, 54.2 mm) and growth rate were lower compared to other Iberian populations of spadefoot toads. However, von Bertalanffy growth curves predict much larger body sizes and greater longevity. We hypothesize that reduced growth rate is a consequence of lengthy, harsh summer conditions. Reduced longevity of spadefoot toads in the study area is probably related to local mortality factors, mainly road kill and land ploughing. Predictions of a postponement of age at sexual maturity at a smaller body size when conditions of reduced feeding and growth rate prevail were only weakly satisfied.