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 ultraviolet-B radiation (UVBR) on amphibian early-embryonic performance, leading to the conclusions, first, that the embryonic stages of many species are 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 many amphibian populations. However, possible carry-over effects of exposure to UVBR in the embryonic stages to the larval stages have received less attention. We studied the effects of UVBR experienced during the embryonic stages (age less than 11 days) on the later performance (age 11-75 days) of common frog, Rana temporaria, larvae. In a factorial laboratory experiment, newly fertilized embryos were divided into three different UVBR treatments (no UVBR (control), 1.25 kJm(-2) (normal) and 1.58 kJm(-2) (26% enhanced)), after which the individual larvae were raised until metamorphosis in the absence of UVBR. No effects of UVBR on embryonic survival rates, frequency of developmental anomalies or hatchling size were found, corroborating the earlier results indicating that R. temporaria embryos are tolerant to UVBR. However, analyses of larval performance revealed that larvae exposed to enhanced levels of UVBR as embryos suffered from an increased frequency of developmental anomalies and metamorphosed later and at a smaller size than larvae that had been protected from UVBR as embryos. These results suggest, in contrast to the earlier studies, that UVBR has direct negative effects on R. temporaria embryos, but these effects are expressed mostly or only during the 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 source of phenotypic variation in fitness.