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- Pahkala, Maarit, et al.
(författare)
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Effects of ultraviolet-B radiation and pH on early development of the moor frog Rana arvalis
- 2001
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Ingår i: Journal of Applied Ecology. - : Wiley. - 1365-2664 .- 0021-8901. ; 38:3, s. 628-636
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Tidskriftsartikel (refereegranskat)abstract
- 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 studied 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 April 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 ambient 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 (50) reduced hatchability, increased frequency of developmental 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 traits. 5. The lack of UV-B radiation effects on the development of R. arvalis embryos cannot be ascribed to relatively low effective daily doses of radiation (c. 043 kJ m2) during the field experiments, as in the laboratory even higher doses at UV-B 125 kJ m2 and 158 kJ m2 (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.
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| 2. |
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| 3. |
- Pahkala, Maarit
(författare)
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Evolutionary ecology of ultraviolet-B radiation stress tolerance in amphibians
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades many amphibian species and populations have experienced declines and extinctions in different parts of the world. Anthropogenic activities are believed to account for these declines, and one of the hypothesized causes has been the increased level of ultraviolet-B (UV-B) radiation due to depletion of the stratospheric ozone layer. Although negative effects of UV-B radiation on development of many amphibian species have been demonstrated, a number of potentially critical issues around assessment of amphibian UV-B radiation tolerance have remained unexplored. For instance, next to nothing is known about geographic variation in UV-B tolerance and about possible carry-over effects of early UV-B exposure to later life-stages. Likewise, synergistic effects with other stressors, as well as sublethal effects on growth have received little attention. The results from field and laboratory experiments show that R. temporaria and R. arvalis are relatively tolerant to even high levels of UV-B in terms of embryonic survival. However, it was found that even normal levels of UV-B can reduce early embryonic growth. In addition, the effects of early exposure to UV-B became manifested mostly or only after a considerable time-lag (i.e. at metamorphosis). Furthermore, it was found that the sublethal effects of UV-B may become manifested only in combination with other stressors, such as low pH, and this synergism may differ among different populations. No evidence for genetic differentiation in UV-B tolerance was found.These findings suggest that even a relatively tolerant species, such as R. temporaria, may be sensitive to increased levels of UV-B radiation, but that this sensitivity may be highly population, environment and trait dependent. The observed carry-over effects over life-stages emphasise the importance of the early life environment on later life fitness.
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| 4. |
- Pahkala, Maarit, et al.
(författare)
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Lethal and Sublethal Effects of UV-B/pH Synergism on Common Frog Embryos
- 2002
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Ingår i: Conservation Biology. - : Wiley. - 0888-8892 .- 1523-1739. ; 16:4, s. 1063-1073
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Tidskriftsartikel (refereegranskat)abstract
- Although the negative effects of ultraviolet-B ( UV-B) radiation on the development of many amphibian species have been demonstrated, some speciessuch as the common frog ( Rana temporaria)seem to be tolerant of UV-B radiation. The amount of UV-B radiation received is likely to vary among populations of the same species, but little is known about geographic variation in UV-B tolerance. Similarly, although UV-B radiation can have synergistic effects with other stressors, no studies have focused on geographic variation of these effects on amphibians. We investigated the synergistic effects of UV-B radiation and low pH on hatchability and early development of R. temporaria embryos in a factorial laboratory experiment with animals originating from southern and northern Sweden. Newly fertilized eggs were exposed to three different UV-B treatments (no UV-B [control, 1.254 k/J/m 2[normal and 1.584 k/J/m 2[26 enhanced) and two pH treatments (4.5 [low and 7.6 [neutral). Ultraviolet-B radiation in combination with low pH lead to markedly (approximately 50) reduced survival rates and increased (approximately 30) frequency of developmental anomalies in the northern but not in the southern population. The UV-B- exposed embryos hatched at smaller size in the southern population, whereas low pH reduced hatchling size in both populations. In both populations and pH treatments, embryos in the normal UV-B treatment developed significantly faster than embryos in the enhanced or control UV-B treatments. No interaction between pH and UV-B on developmental rates or hatchling size was detected. The results demonstratecontrary to earlier beliefthat R. temporaria embryos are not insensitive to increased levels of UV-B radiation. The lethal effects of UV-B radiation may, however, become manifested only in combination with other stressors, such as low pH, and the effects of this synergism may differ among different populations of the same species.
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