Effects of ultraviolet-B radiation on common frog Rana temporaria embryos from along a latitudinal gradient.

Interspecific variation in ultraviolet-B (UV-B) radiation tolerance in amphibians is well established, but little is known about the possible intraspecific variation in UV-B radiation tolerance within any species. We studied the effects of UV-B radiation on common frog Rana temporaria embryos originating from eight populations spanning a 1,200 km latitudinal gradient across Sweden. Newly fertilised eggs were exposed to three different UV-B treatments [absent (no UV-B), normal (1.254 kJ m-2) and enhanced (1.584 kJ m-2, 26% above normal) levels] in a laboratory, and effects on survival, frequency of developmental anomalies, developmental rate and hatchling size were documented. UV-B radiation treatments did not have main factor effects on embryonic mortality or frequency of developmental anomalies. Survival to hatching was lower at higher latitudes, but it was independent of UV-B treatments. High UV-B treatment prolonged development time in five populations, whereas in one population development time was longest in the absence of UV-B. Even though the northernmost populations had the shortest development times, the interaction between latitude and development time was not significant. There was a significant population×UV-B interaction in hatchling size, indicating that hatchling size was negatively affected by the UV-B treatments in some of the populations. Hatchling size increased until mid-latitudes and was again somewhat smaller at the northernmost latitudes, but this was independent of UV-B treatments. These results suggest that although R. temporaria embryos are rather tolerant of UV-B radiation, and there is no clear latitudinal pattern to UV-B tolerance in this species, the sublethal effects of UV-B on embryonic development may differ among different populations.