Does simultaneous UV-B exposure enhance the lethal and sub-lethal effects of aquatic hypoxia on developing anuran embryos and larvae?

Recent catastrophic global amphibian declines have been partially linked to increases in UV-B radiation as a consequence of stratospheric ozone depletion. Previous studies have shown that in the presence of other environmental stressors including aquatic pH and temperature and the presence of contaminants or pathogens, the lethal effects of UV-B on amphibian larvae are enhanced due to interactions between the stressors. Little is known about the interactions between UV-B and aquatic hypoxia, a common and significant natural stressor of amphibian larvae. We examined the potential effects of UV-B and aquatic hypoxia in combination on embryonic survival, developmental rate, body mass and locomotor performance of embryos and larvae of the striped marsh frog, Limnodynastes peronii. We found that while both UV-B and hypoxia independently had substantial negative effects on the developing embryos of L. peronii, they did not interact in a multiplicative or antagonistic manner. The effects of the stressors in combination were as might be predicted based on the knowledge of their independent actions alone (i.e. an additive effect). In all cases developing embryos exposed to both UV-B and hypoxia were more severely affected than those exposed to either UV-B or hypoxia alone. The results of this study show the importance of examining both the direct actions of individual stressors and how these may be influenced by the presence of other environmental factors.