Use of bone histology in estimating the age of frogs (Rana perezi) from a warm temperate climate area

The structure and the histological expression of annual bone growth marks of Iberian water frogs (Rana perezi) from a warm temperate climate region (southwestern Spain) differ markedly from the pattern observed in colder climate populations. Forty-eight percent of winter growth marks appeared to be annuli; 52% are lines of arrested growth but 20% of these are weakly expressed. Annuli or lines of arrested growth were very diffuse or absent in 7% of the 103 individuals studied, suggesting that variations in climate have a stronger influence on growth-mark formation than was previously considered. Males and females are sexually mature in their second year, although some males mature at 1 year of age and some females at 3 years. The oldest males were 4 years old, 1 year younger than males from northern populations. The oldest female was 6 years old. The wide range of body sizes among the 1-year-old froglets can be explained by the extended period of metamorphosis, from July to November.