A cataract is a clouding of the lens that reduces light transmission to the retina, and it decreases the visual acuity of the bearer. The prevalence of cataracts in natural populations of mammals, and their potential ecological significance, is poorly known. Cataracts have been reported to arise from high levels of oxidative stress and a major cause of oxidative stress is ionizing radiation. We investigated whether elevated frequencies of cataracts are found in eyes of bank voles Myodes glareolus collected from natural populations in areas with varying levels of background radiation in Chernobyl. We found high frequencies of cataracts in voles collected from different areas in Chernobyl. The frequency of cataracts was positively correlated with age, and in females also with the accumulated radiation dose. Furthermore, the number of offspring in female voles was negatively correlated with cataract severity. The results suggest that cataracts primarily develop as a function of ionizing background radiation, most likely as a plastic response to high levels of oxidative stress. It is therefore possible that the elevated levels of background radiation in Chernobyl affect the ecology and fitness of local mammals both directly through, for instance, reduced fertility and indirectly, through increased cataractogenesis.
Cataracts were found in 57 out of 80 voles from Chernobyl (71%). Females and males had cataracts at roughly equal frequency (males: 73%, females 67%, Table 1). While the cataract score increased with age in both sexes, the influence of accumulated radiation dose on cataract score differed between female and male voles (Table 2a). Therefore the data were split by sex and re-analysed. The interaction between age and accumulated radiation dose was not significant in either sex (females: F1, 23 = 0.092, P = 0.764; males: F1, 44 = 0.396, P = 0.533) and removed from the final model. The frequency of cataracts was positively correlated with age in both females and males (Fig. 1A,B), and age explained a significant amount of the variance in cataract scores in both sexes (Table 2b,c). In addition, the frequency of cataracts was also positively correlated with accumulated radiation dose. However, this effect was only significant for female voles, but not for the male voles (Table 2b,c, Fig. 1C,D). Finally, in the analysis of female litter size the interaction between cataract score and age was non-significant and removed (F1, 10 = 4.078, P = 0.071) after which the analysis was redone with only the main effects. Number of offspring in pregnant female voles was positively correlated with age and strongly negatively correlated with cataract score (Full model: F2, 11 = 14.916, P = 0.001; Age: F1, 11 = 23.194, P = 0.001; Cataract score: F1, 11 = 25.901, P < 0.001; Random factors: estimate ± residual: 0.105 ± 0.111, z = 0.941, P = 0.347, Fig. 2). Overall all results stay unchanged if only animals from 2011 (the majority of samples) were analysed (data not shown).
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Data: 27.01.2016
Fonte: www.nature.com
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