| Under the dual impact of human activities such as climate warming and globalization,biological invasion has become one of the key issues of concern for all countries.The invasive organisms represented by the apple snails pose a great threat to China’s agricultural production and people’s health.In March 2003,the State Environmental Protection Administration listed the apple snails in the black list of exotic species,and the Twentieth National Congress proposed the goal of strengthening biosafety management and preventing the invasion of exotic species.As a representative species of invading China,apple snail is native to the Amazon basin of South America,with strong fertility and mixed feeding habits.Because of its high protein content,apple snail was introduced into China as an economic animal,in the 1980 s.Due to the lack of natural enemies,and the blind breeding and random discarding of the masses,the apple snails spread rapidly in China,seriously damaging biodiversity.In addition,the eggs of the apple snails are pink,which seriously affects the aesthetic value of the waterfront landscape.According to statistics,apple snails have invaded 246 counties(cities)in 13 provinces of China and are continuing to spread.Therefore,it is urgent to strengthen the physiological and biochemical research of the apple snails and explore the interaction mechanism between them and the environment.Starting from molecular biology,this paper has carried out molecular identification of the apple snails in Guangzhou,Shanghai and Chengdu from a microscopic perspective to explore their variation in the process of invasion and diffusion;At the same time,combined with morphological observation,we can compare and judge the direct differences between samples from different places.On this basis,the effects of environmental stress on the activity of superoxide dismutase(SOD)and the content of malondialdehyde(MDA)in the liver and pancreas of the apple snails were analyzed by measuring physiological and biochemical indicators,and the relevant control strategies were put forward.Finally,by studying the changes of microorganisms and water quality in the water environment where the apple snails live,the interaction mechanism between the apple snails and the water body is clarified,in order to provide a theoretical basis for the prevention and control of the apple snails.(1)The results of morphology and molecular identification showed that there was no genetic variation in the apple snails from Guangzhou,Shanghai and Chengdu.The samples from the three places belonged to Pomacea canaliculata and Pomacea maculata.The samples from Guangzhou were Pomacea canaliculata and Pomacea maculata,The samples in Chengdu are all small tube apple snails.The results showed that the small tube apple snails had a wider distribution range and stronger invasiveness than the spotted apple snails,and attention should be paid to distinguish them in terms of prevention and control.(2)The sharp change of environmental factors will affect the fluctuation of the content of antioxidants in the body of apple snails.SOD and MDA are related substances of antioxidant stress response,so they can be used to characterize the response of apple snails to environmental stress.This experiment showed that under the stress of temperature,dissolved oxygen and salinity,the SOD activity and MDA content of the hepatopancreas of the three places of the apple snails in Guangzhou,Shanghai and Chengdu increased first and then decreased,and reached the maximum value at24h～48h,and returned to the initial level at 72 h,but the relative values were different.Under the combined temperature-salinity stress,the change trend of SOD activity and MDA content in the hepatopancreas of the apple snails was consistent with that of the single factor stress,but the value was higher than that of the single factor stress,and the temperature and salinity showed a synergistic effect.The temperature stress experiment showed that there was a risk of invasion to the low temperature area;The salinity stress experiment showed that the apple snails had the risk of invading into the saline region.(3)The apple snails will make the water body appear weakly acidic,and gradually tend to be neutral with the increase of time.The total nitrogen(TN)and total phosphorus(TP)in the water body are significantly increased,in which the TN on the fifth day is 9 times of that on the tenth day,and the TP on the seventh day is 10 times of that on the first day.α In terms of diversity,the Chao1 index of water microorganisms in the control group was higher than that in the experimental group from day 0 to day 5,but showed a continuous downward trend;The Chao1 index of the experimental group decreased in a fluctuating manner.From the 5th to the 8th day,the Shannon index and Simpson index of water microorganisms in the experimental group were higher than those in the control group,and began to decline on the 8th day;From the 9th day,the Shannon index and Simpson index of water microorganisms in the experimental group showed an upward trend.The Pielou index of water microorganisms in the control group generally showed a downward trend,while the Pielou index of water microorganisms in the experimental group fluctuated up and down.β In terms of diversity,the distance matrix and PCo A analysis showed that the sample heterogeneity between the experimental group and the control group was strong,and the sample heterogeneity in the control group was greater than that in the experimental group.NMDS analysis showed that there were significant differences in microbial communities between the control group and the experimental group.The distribution analysis of microbial community diversity showed that there were differences in the microbial community structure of water microorganisms with average relative abundance greater than 1% at the class level between the experimental group and the control group.A total of 10 and 13 classes were found respectively,of which the control group contained α-Proteobacteria γ-Proteobacteria,actinomycetes and Bacteroides;The microbial group of the experimental group contains γ-Proteobacteriaα-There are five dominant classes of bacteria,including Proteobacteria,Bacteroides,Actinobacillus and Acidomycetes.Compared with the control group,the microbial community structure of the experimental group was significantly different.The distribution of microbial community structure in the experimental group was disorderly,and the dominant bacteria(γ-Proteobacteria α-Proteus)is higher than the control group. |
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