1. Although the potential negative effects of increased ultraviolet-B (UV-B
) radiation on early life stages of aquatic organisms are widely recognized
, possible synergistic effects with other stressors have seldom been studie
d outside the laboratory. We investigated the effects of UV-B radiation and
pH on hatchability and early development of moor frog Rana arvalis eggs in
the field and in laboratory experiments conducted during April 1998 and Ap
ril 2000 in central Sweden.
2. In the field experiments, no evidence was found for reduced hatchability
or increased frequency of developmental anomalies of embryos exposed to am
bient levels of UV-B compared with embryos shielded from UV-B radiation.
3. Hatchlings shielded from ambient UV-B radiation did not grow larger than
their exposed full-sibs, giving no support to the hypotheses that (i) the
repair of cellular UV-B damage might be energetically costly nor (ii) that
UV-B-induced photoproducts directly reduce growth.
4. Although low pH (5.0) reduced hatchability, increased frequency of devel
opmental anomalies and reduced early embryonic growth in R. arvalis, there
was no evidence for synergistic effects of pH and UV-B on any of these trai
ts.
5. The lack of UV-B radiation effects on the development of R. arvalis embr
yos cannot be ascribed to relatively low effective daily doses of radiation
(c. 0.43 kJ m(-2)) during the field experiments, as in the laboratory even
higher doses at UV-B 1.25 kJ m(-2) and 1.58 kJ m(-2) (all DNA weighed) had
no negative effects.
6. These results suggest that current levels of UV-B radiation in northern
Europe are not likely to reduce fitness in natural populations of the moor
frog, even in areas already stressed by acidity.