Effect Of UVA Radiation On Biological Fitness And Antioxidant System Of Fruit Fly, Drosophila Melanogaster

Phototaxis is a common phenomenon in insects, and many insects exhibit positive response to light, which has been used widely to control populations of many types of insect pest. The spectral preferences, physiologic perception of light had been well studied all over the world. However, the mechanism of phototaxis is also not clear. The fruit fly, Drosophila melanogaster, is a diurnal insect display a conspicuous positive photo tactic behavior to light stimuli, especially to black light (UVA). To elucidate the phototaxis mechanism, we test the lifehistory fitness and physiolical responses. We use the high (200±25μw/cm2) and low (10±5μw/cm2) intensity of UVA light to irradiate Drosophila melanogaster for different exposure times (1h,2h,3h), and the effects on adult longevity and fecundity, F1 generation development were reflected. We also test responses of the lipid peroxidation, total antioxidant capacity, and antioxidant enzymes of adult flies under different UVA radiation and during different ages of flies. The main results are as follows:1. The effects of UVA radiation on lifespan and fecundity of fruit fly adults.The lifespan showed that the longevity by UVA radiation was longer than the control, and there were significant differences in intensity (p<0.001). The mean lifespan of flies in short exposure time was longer than that of longer exposure time, in the high intensity of UVA. While, in the low intensity, the lifespan both female and male were increasing with the exposure time extending. The fecundity tests showed that there were no significant effects on the lifetime fecundity neither in intensity nor exposure time of UVA radiation. However, all the UVA irradiation assays have more egg production than the ck. With exposure time prolonging, the lifetime reproduction were increasing in both UVA intensity, especially the 3h traits in low UVA intensity increased more. All in all, the low UVA intensity was of benefit to adults'fitness.2. The effects of UVA radiation on survivorship and development time of F1 generation of D. melanogaster.The survivorship from egg to eclosion showed that there were no significant effects of neither intensity nor the exposure time, only the 2h assay in low UVA had higher survivorship than the control. The development time data revealed a significant effect of main effect of UVA intensity (p< 0.001), but no difference among the exposure times (p =0.097), whereas the differences were reflected in a significant UVA intensity×Exposure time interaction. The flies in all the UVA irradiations developed slower than the control, significantly, among light regimes in high and low intensity. The results of survivorship and development time revealed that the UVA radiation was harmful to pre-adult's fitness, at least a partial effect.3. The effects of different intensity and exposure time of UVA radiation on antioxidant responses of D. melanogaster.There were significant differences on malonaldehyde (MDA) content, total antioxidant capacity, catalase (CAT) and peroxidases (POD) activity between the sexes. And the total antioxidant capacity (p< 0.001) and CAT (p= 0.004) activity were different between the intensities of UVA. No difference among the exposure time, while the interactions of UVA intensity×Exposure time were existed. To the male, in 30min high UVA radiation, the MDA content was higher, but the total antioxidant capacity was lower than those of ck, POD activity higher than 60min's. And in the low UVA radiation, CAT and glutathione-S-transferase (GST) activity were higher than the ck, which was in 120min. To the female, only 60min of high radiation was lower in total antioxidant capacity than 30min's. And in low intensity, MDA content was higher than ck in 60min and 120min, total antioxidant capacity and superoxide dismutase (SOD) activity were higher in 60min, all the CAT maintain higher activity, compared with ck.4. The effects of UVA radiation on antioxidant responses of D. melanogaster in different ages.In fly adults, Age-related changes in MDA content and SOD activity followed a bell-shaped trend, with increase during the first 2 or 4 weeks of life followed by a sharp decrease during the latter part of life, whereby the level of activity was similar in the very young and the very old flies. The POD activitie was linearly decline during 42 days, and then slightly increased. The CAT and GST activity were different changes in male and female, and both of them in female were increase with age of the flies, which relate to long life span. But CAT activity tends to slightly increase during young age and sharply decrease in the latter, in contrast GST activity declined first and then increased. The total antioxidant capacity tend was undulate, especially in the male, which is combination of all the antioxidant defenses.The above research showed that, the development time of F1 generation was longer in the UVA radiation, and the longevity was longer and egg production was more in UVA radiation, especially in low intensity, but The activity of SOD, CAT, POD and GST were contributing to control the low level of ROS, which caused by UVA radiation. In the old age, the continual high UVA radiation reduced activity of antioxidant enzymes, which was bad work in slowing the senescence down. In total, the effects of UVA radiation are depending on the intensity and exposure time.