Induction of photolyase activity in wood frog (Rana sylvatica) embryos

Impacts of UVB radiation on food consumption of forest specialist tadpoles

Solar ultraviolet radiation B (UVB) is an important environmental stressor for amphibian populations due to its genotoxicity, especially in early developmental stages. Nonetheless, there is an absence of works focused on the UVB effects on tadpoles' food consumption efficiency. In this work, we investigated the effects of the exposure to a low environmental-simulated dose of UVB radiation on food consumption of tadpoles of the forest specialist Hypsiboas curupi [Hylidae, Anura] species. After UVB treatment tadpoles were divided and exposed to a visible light source or kept in the dark, in order to indirectly evaluate the efficiency of DNA repair performed by photolyases and nucleotide excision repair (NER), respectively. The body mass and the amount of food in tadpoles' guts were verified in both conditions and these data were complemented by the micronuclei frequency in blood cells. Furthermore, the keratinized labial tooth rows were analyzed in order to check for possible UVB-induced damage in this structure. Our results clearly show that the body weight decrease induced by UVB radiation occurs due to the reduction of tadpoles' food consumption. This behavior is directly correlated with the genotoxic impact of UVB light, since the micronuclei frequency significantly increased after treatments. Surprisingly, the results indicate that photoreactivation treatment was ineffective to restore the food consumption activity and body weight values, suggesting a low efficiency of photolyases enzymes in this species. In addition, UVB treatments induced a higher number of breaks in the keratinized labial tooth rows, which could be also associated with the decrease of food consumption. This work contributes to better understand the process of weight loss observed in tadpoles exposed to UVB radiation and emphasizes the susceptibility of forest specialist amphibian species to sunlight-induced genotoxicity.

Identification of influential events concerning the Antarctic ozone hole over southern Brazil and the biological effects induced by UVB and UVA radiation in an endemic treefrog species

The increased incidence of solar ultraviolet radiation (UV) due to ozone depletion has been affecting both terrestrial and aquatic ecosystems and it may help to explain the enigmatic decline of amphibian populations in specific localities. In this work, influential events concerning the Antarctic ozone hole were identified in a dataset containing 35 years of ozone measurements over southern Brazil. The effects of environmental doses of UVB and UVA radiation were addressed on the morphology and development of Hypsiboas pulchellus tadpole (Anura: Hylidae), as well as on the induction of malformation after the conclusion of metamorphosis. These analyzes were complemented by the detection of micronucleus formation in blood cells. 72 ozone depletion events were identified from 1979 to 2013. Surprisingly, their yearly frequency increased three-fold during the last 17 years. The results clearly show that H. pulchellus tadpole are much more sensitive to UVB than UVA light, which reduces their survival and developmental rates. Additionally, the rates of micronucleus formation by UVB were considerably higher compared to UVA even after the activation of photolyases enzymes by a further photoreactivation treatment. Consequently, a higher occurrence of malformation was observed in UVB-irradiated individuals. These results demonstrate the severe genotoxic impact of UVB radiation on this treefrog species and its importance for further studies aimed to assess the impact of the increased levels of solar UVB radiation on declining species of the Hylidae family.

Beyond xeroderma pigmentosum: DNA damage and repair in an ecological context. A tribute to James E. Cleaver

The ability to repair DNA is a ubiquitous characteristic of life on Earth and all organisms possess similar mechanisms for dealing with DNA damage, an indication of a very early evolutionary origin for repair processes. James E. Cleaver's career (initiated in the early 1960s) has been devoted to the study of mammalian ultraviolet radiation (UVR) photobiology, specifically the molecular genetics of xeroderma pigmentosum and other human diseases caused by defects in DNA damage recognition and repair. This work by Jim and others has influenced the study of DNA damage and repair in a variety of taxa. Today, the field of DNA repair is enhancing our understanding of not only how to treat and prevent human disease, but is providing insights on the evolutionary history of life on Earth and how natural populations are coping with UVR-induced DNA damage from anthropogenic changes in the environment such as ozone depletion.

Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape

Increasing UV-B radiation (UV-B; 290-320 nm) due to stratospheric ozone depletion has been a leading explanation for the decline in amphibians for nearly 2 decades. Yet, the likelihood that UV-B can influence amphibians at the large spatial scales relevant to population declines has not yet been evaluated. A key limitation has been in relating results from individual sites to the effect of UV-B for populations distributed across heterogeneous landscapes. We measured critical embryonic exposures to UV-B for two species of montane amphibians with contrasting physiological sensitivities, long-toed salamander (Ambystoma macrodactylum) and Cascades frog (Rana cascadae), at field sites spanning a gradient of UV-B attenuation in water. We then used these experimental results to estimate the proportion of embryos exposed to harmful UV-B across a large number of breeding sites. By combining surveys of the incubation timing, incident UV-B, optical transparency of water, and oviposition depth and light exposure of embryos at each site, we present a comprehensive assessment of the risk posed by UV-B for montane amphibians of the Pacific Northwest. We found that only 1.1% of A. macrodactylum and no R. cascadae embryos across a landscape of breeding sites are exposed to UV-B exceeding lethal levels. These results emphasize that accurately estimating the risk posed by environmental stressors requires placing experimental results in a broader ecological context that accounts for the heterogeneity experienced by populations distributed across natural landscapes.

Expression of the DNA repair enzyme, photolyase, in developmental tissues and larvae, and in response to ambient UV-R in the Antarctic sea urchin Sterechinus neumayeri

Gene expression of the DNA repair enzyme, photolyase (E.C. 4.1.99.3) was examined in the gonads, eggs, embryos and larval stages of the Antarctic sea urchin, Sterechinus neumayeri. Partial sequencing of the gene revealed two highly conserved regions, including a 300 bp region representing the binding site for the cofactor flavin adenine dinucleotide. The second 1200 bp region, likely representing a second light-harvesting cofactor binding site, was identified in a second sea urchin species, Strongylocentrotus frascicanus. Probes for photolyase were developed from the shorter sequence, and expression in sea urchin developmental tissue and stages, and in response to in situ exposure to ultraviolet radiation was quantified using PCR and RT-qPCR, with concentrations of photolyase normalized to actin concentrations. Photolyase was expressed in all tissues and developmental stages examined. In controlled field-based experiments in McMurdo Sound, Antarctica, we found evidence of both constitutive expression of photolyase and induction in response to in situ exposure of embryos to UV-R. Induction of photolyase was observed in response to greater ambient UV-R (such as shallower water depths or sea ice-free regions).

Impact of UV-B exposure on amphibian embryos: linking species physiology and oviposition behaviour

Increasing ultraviolet-B radiation (UV-B) has recently captured the attention of ecologists as a key environmental stressor. Certain species may be particularly vulnerable as a result of either high natural exposure to UV-B or limited physiological capacity to withstand it. UV-B sensitivity has been examined at the cellular and individual level for a wide variety of taxa, but estimates of exposure to UV-B in natural systems are lacking and predictions of large-scale impacts are therefore limited. Here, we combine data on the physiological sensitivity to UV-B and patterns of field exposure across sites for embryos of several well-studied US Pacific Northwest amphibian species. We find substantial differences among species' physiological abilities to withstand UV-B and in the level of UV-B exposure of embryos in the field. More specifically, we find that species with the highest physiological sensitivity to UV-B are those with the lowest field exposures as a function of the location of embryos and the UV-B attenuation properties of water at each site. These results also suggest that conclusions made about species' vulnerability to UV-B in the absence of information on field exposures may often be misleading.

Amphibian defenses against ultraviolet-B radiation

As part of an overall decline in biodiversity, amphibian populations throughout the world are disappearing. There are a number of potential causes for these declines, including those related to environmental changes such as increasing ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion. UV-B radiation can kill amphibian embryos or can cause sublethal effects that can harm amphibians in later life stages. However, amphibians have defenses against UV-B damage that can limit damage or repair it after exposure to UV-B radiation. These include behavioral, physiological, and molecular defenses. These defenses differ interspecifically, with some species more able to cope with exposure to UV-B than others. Unfortunately, the defense mechanisms of many species may not be effective against increasing persistent levels of UV-B radiation that have only been present for the past several decades due to human-induced environmental damage. Moreover, we predict that persistent UV-B-induced mortality and sublethal damage in species without adequate defenses could lead to changes in community structure. In this article we review the effects of UV-B radiation on amphibians and the defenses they use to avoid solar radiation and make some predictions regarding community structure in light of interspecific differences in UV-B tolerance.

Photolyase activity of the embryo and the ultraviolet absorbance of embryo jelly for several Ontario amphibian species

Organisms whose eggs develop at or near the interface between air and water may be particularly vulnerable to damage from ultraviolet radiation. The primary form of ultraviolet B (UV-B) radiation damage to biological systems is the formation of cyclobutane pyrimidine dimers (CBPDs) in DNA. The most common method of repairing this damage is photoenzymatic repair via photolyase, whose actions are specific to CBPDs. We utilized a bacterial-transformation assay to estimate the level of photolyase activity of various tissue types in seven species of amphibians collected in south-central Ontario. In this assay, the photolyase activity of a species is measured as the rate of CBPD removal from UV-B-damaged plasmid DNA by cell-free extracts created from the tissue of the species in question. The depth of oviposition and the UV-B absorbance of the embryo jelly, two variables that alter an embryo's in situ exposure to UV-B radiation, were measured to determine whether the level of photolyase activity was correlated with expected UV-B exposure. In vitro measurements of photolyase activity for the seven species were significantly different (F[6]= 10.31, p < 0.0001) and tended to be positively correlated with expected in vivo exposure to UV-B radiation.