Ambient ultraviolet-B radiation reduces hatchling size in the common frog Rana temporaria

Effects of ambient UV-B radiation and pH on hatchability and early developm ent of Rana temporaria embryos were studied in field experiments conducted at two sites in Sweden. In neither of the populations did we find clear evi dence for reduced hatchability or increased frequency of developmental anom alies of embryos exposed to ambient UV-B levels. However, in both populatio ns hatchling size was significantly larger in UV-B blocked as compared to c ontrol treatments, suggesting that ambient UV-B levels had a negative effec t on early growth of embryos. This result is consistent with the hypothesis that the cellular UV-B damage repair mechanisms are costly and trades-off against early growth. Alternatively, UV-B induced photoproducts inhibiting DNA-transcription and thereby protein synthesis may directly reduce growth rare. Although low pH (5.0) had negative effects on hatchability and early embryonic growth, there was no evidence for synergistic effects of pH and U V-B on hatchability, frequency of developmental anomalies or early growth. The results suggest that increased levels of UV-B radiation may cause fitne ss loss in natural populations of the common frog.