Carry-over effects of ultraviolet-B radiation on larval fitness in Rana temporaria

A number of studies have failed to find evidence for negative effects of ul traviolet-B radiation (UVBR) on amphibian early-embryonic performance, lead ing to the conclusions, first, that the embryonic stages of many species ar e tolerant to UVBR, and second, that the increased amount of UVBR reaching the Earth's surface is not likely to have any direct negative effects on ma ny amphibian populations. However, possible carry-over effects of exposure to UVBR in the embryonic stages to the larval stages have received less att ention. We Studied the effects of UVBR experienced during the embryonic sta ges (age less than 11 days) on the later performance cage 11-75 days) of co mmon frog, Rana temporaria, larvae. In a factorial laboratory experiment, n ewly fertilized embryos were divided into three different UVBR treatments ( no UVBR (control), 1.25 kJ m(-2) (normal) and 1.58 kJ m(-2) enhanced)), aft er which the individual larvae were raised until metamorphosis in the absen ce of U-VBR. No effects of UVBR on embryonic survival rates. frequency of d evelopmental anomalies or hatchling size were found, corroborating the earl ier results indicating that R. temporaria embryos are tolerant to UVBR. How ever, analyses of larval performance revealed that larvae exposed to enhanc ed levels of UVBR as embryos suffered from an increased Frequency of develo pmental anomalies and metamorphosed later and at a smaller size than larvae that had been protected from UVBR as embryos. These results suggest, in co ntrast to the earlier studies, that UVBR has direct negative effects on R. temporaria embryos. but these effects are expressed mostly or only during t he later life stages. To this end., our results support the contention that carry-over effects from one life stage to another may be an important sour ce of phenotypic variation in fitness.