| Rotifers are the main groups of zooplankton and often used in ecotoxicology studies because of its propagation speed,short life cycle and high sensitivity to toxicants.At present,most studies on ecotoxicology are concentrated on Brachlonus calyclflorus,but few reports are available on the ecotoxicological effects of predatory rotifers such as Asplanchna brightwelli.Because the latter is larger than the formerand its activity is slow and easy to count,many scholars suggest it as an indicator of water environment monitoring.Testosterone and estradiol are steroid hormones secreted by vertebrates and cause endocrine disruption of plankton.In this paper,We used Asplanchna brightwelli as the test animal,aimed to explore the typical steroid hormones testosterone,estradiol,respectively,as well as quantitative effects on reproductive of rotifera.We further studied the enzyme activity of rotifer exposed two hormones,thus to investigate the reliability of the ecophysiological indicators of endocrine disruption.The main results are as follows:1.Testosterone,estradiol acute toxicity test(LCso)The experimental results showed that the 48h LC50 of testosterone to Asplanchna brightwelli was 9.56 mg/L,the linear regression equation was Y=1.9793X+3.0591(R2=0.9211),the 95%confidence interval was 2.74-33.40 mg/L;The 48h LC50 of estradiol to Asplanchna brightwelli was 8.18 mg/L,The linear regression equation was Y=3.5292X+1.7788(R2=0.9195).The 95%confidence interval was 3.07-21.77 mg/L.The results showed that after the treatment of testosterone and estradiol,Asplanchna brightwelli appeared significantly toxic effects,the mortality rate increased with the drug concentration increased.It means Asplanchna as animal subjects can accurately evaluate two kinds of drug toxicity.2.The effects of testosterone and estradiol on the population parameters of Asplanchna brightwelliThe experimental culture temperature was 25+1?,the light intensity was about 40001x,the day length ratio L:D = 12:12.After exposure to testosterone and estradiol at 1.0,2.0,4.0 and 8.0 mg/L,the population density,population growth rate,male ratio and resting egg yield of Asplanchna brightwelliwere studied.From the experimental results,we can draw:Both hormones had effects on the reproduction of Asplanchna brightwelli,the inhibition of population growth on rotifers was more obvious with increase of drug concentration.The difference between the 4d groups was the most obvious.Compared with the control group,the population growth rates were 0.74 and 0.55 exposed to 4 and 8.0 mg/L testosterone respectively,which were 10.77%and 33.58%lower than the control group respectively.Similar to testosterone,the population growth rates were 0.80,0.74 and 0.61 at day 4 with estradiol concentrations of 1.0,4.0 and 8.0 mg/L respectively,which were significantly lower than those in control group by 12.92%,18.70%and 33.53%(P<0.05).With the increase of two hormones concentration,the inhibitory effects on male and resting eggs of Asplanchna brightwelliwere more obvious.The testosterone and estradiol treatment groups at 8 mg/L completely inhibited the resting oviposition of rotifer.3.Effects of testosterone and estradiol on the reproduction and life span of Asplanchna brightwelli respectivelyWith the increase of testosterone concentration,Asplanchna brightwelliprolonged its reproductive period and shortened the average life expectancy,while the number of offspring individuals gradually decreased.The reproductive period was 11.71%(P<0.05)longer than the control group,but no significant change in the other groups(P>0.05)exposed to testosterone 8.0mg/L.Except the 0.5mg/L testosterone,the average life span of each treatment group was significantly shortened and the number of offspring individuals was significantly decreased(P<0.05).Compared with the control group,the average life expectancy was shortened by 21.91%,35.61%,35.00%and 52.22%,and the number of offspring decreased by 31.63%,69.22%,60.51%and 82.20%when exposed to 1.0,2.0,4.0 and 8.0 mg/L testosterone respectively,the difference was significant(P<0.05).Similar to testosterone,with the increase of estradiol concentration,Asplanchna brightwellipro longed its reproductive period and shortened the average life expectancy,while the number of offspring individuals gradually decreased.The reproductive period were 6.74%and 7.10%longer than the control group(P<0.05)when exposed to 4,0 and 8.0 mg/L estradiol.Compared with the control group,the average life span of rotifers were shortened by 21.49%,27.72%,34.58%,39.09%and 49.75%respectively,and the number of offspring were decreased by 24.44%,38.67%,46.22%,49.44%and 80.33%respectively when exposed to 0.5,1.0,2.0,4.0 and 8.0mg/L estradiol.4.The effects of testosterone and estradiol with a total concentration of 8mg/L on population growth and reproduction of Asplanchna brightwelliThe combination of testosterone and estradiol had a significant effect on the population growth rate of Asplanchna brightwelli,with the most significant difference between the 5th day.On the whole,with combination of testosterone and estradiol concentration increased,r value decreased.The combination of testosterone and estradiol had significant effects on reproductive period,mean life span and the number of offspring individuals of Asplanchna brightwelli.With the concentrations of ToEs,T2E6 and TsEo,reproductive period was significantly increased by 34.17%,48.01%and 43.57%respectively(P<0.05).Compared with the control group,the average life span and the number of offspring of each treatment group were significantly lower than the control group,the difference was extremely significant(P<0.001).Thus,in combinations of testosterone and estradiol,estradiol has a greater effect on survival and reproduction of rotifer,both of them showed significant synergistic effects.5.The effects of testosterone and estradiol on some enzyme activities of rotiferWith the increase of estradiol and testosterone concentrations,the content of SOD and CAT in Asplanchna brightwelli first increased and then decreased.The activity of SOD and CAT in each treatment group was higher than that in the control group.The SOD activity of rotifer reached its peak when the testosterone concentration was 2.0mg/L(P<0.05).The CAT activity was the highest at the concentration of lmg/L(P<0.05).When the concentration of estradiol was 1.0 mg/L,the activity of SOD in rotifers peaked(P<0.05).At the concentration of 0.5 mg/L,CAT activity was the highest,with significant difference(P<0.05). |
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