| Water pollution indicates that the amount of the discharged pollutants exceed the concentration and environmental capacity of the water body,which result in destroys of the physical,chemical,and biological characters of the water body.Water pollution causes inevitable damage to animals,plants and microorganisms living in or around the water.Plants and microorganisms are able to metabolize pollutants and synthesize their own nutrients,and they show tolerance and toxicity conversion;therefore they indicate adaptation to the pollution environment.However,the pollutants cannot be metabolized by animals,moreover,the animal cells are fragile and normally they show lower endurance to water pollutants comparing to plants and microbes.How animal' adapt in polluted water environment?Whether there are different adaption abilities accompanying ploidy or not?What is the adaptation mechanism?All these questions are still under survey.Lake Dianchi is known as the Plateau Pearl,its water quality has undergone significant changes in the past four decades.In the past 40 years,the water quality in Lake Dianchi had been worsening from the clear type III down to the heavy pollution of type V or even worse.From 2013,since diverting water from River Niulan,the water quality in Lake Dianchi has been gradually improved.The survey and literature revealed that,1)the proportion of 2N/3N individuals in the Carassius auratus complex population varies in differently polluted positions of Lake Dianchi;2)during the period of water quality of type III,the ratio of 2N was more than 40%,while during the period of the water quality of type V and even worse,the ratio of 2N decreased dramatically down to 5%;3)and in recent 10 years,we have not found any individuals of 2N in the Grass sea part of Lake Dianchi,which is highly polluted;while 3N showed as a dominant population in samples.Whether 3N population is more adaptive than its 2N inidividuals in the polluted water?What is the genomic basis for their adaptation?What are the similarities and differences of adaptation between 3N and 2N?These questions need to be further investigated.In order to explore the adaptation ability of wild C.auratus complex with two ploidy(2N/3N)based on the previous long-term sample collection,we firstly sampled 2N and 3N individuals from positions with different levels of pollution in Lake Dianchi and Erhai(2005-2009,2015-2016);meanwhile,in order to increase the efficiency of ploidy detection,we developed two methods to help identify 2N/3N individuals quickly,based on the morphological differences between 2N and 3N;secondly,we investigated the correlation between the water quality and the distribution ratios of different ploidy in wild C.auratus complex;lastly,by integrating the environmental factors and the transcriptomic data,on the one hand,we analyzed the relationship between water pollution factors and diploid distribution ratios;on the other hand,we analyzed the differences of expressional patterms between two types of ploidy in wild C.auratus complex from different or same positions in Lake Dianchi,and found the candidate genes and regulation pathway that might be related to the adaptations of 2N/3N C.auratus.The results are as following,In the first part,we found significant difference in the morphological characteristics between 2N and 3N based on two methods of principal component analysis and machine learning.1)Principal component analysis was conducted.The comparison between quantified datasets of body color,body height/body length and head angle in 2N and 3N indicated significant differences,which could help distinguish only 80%individuals with different ploidy;2)in order to identify the 2N/3N individuals more effectively,we developed the methods based on machine learning and the accuracy rate of ploidy identification was improved to 96%.Additionally,there existed several individuals whose ploidy could not be distinguished by both methods.In order to explore their genetic difference,we hired the phylogenetic analyses of D-loop obtained from Sanger sequencing.The results indicated that some 3N shared the same branch with 2N,which had been confirmed of deriving from 2N.It suggested the 3N with similar morphological traits to 2N and sharing the same haplotype of D-loop with 2N might be recently established from diploid relative.The' results might also indicated the cause of error rate during ploidy identification by both methods.In the second part,integrated the results of ploidy survey and water quality parameters of Lake Dianchi,we analyzed their correlation and the results showed,1)the correlations between the distribution of 2N and total phosphorus,ammonia nitrogen,transparency were significant positive,which suggested the promoting factors for 2N survival;2)the correlations between the distribution of 2N and fluoride,permanganate index were significant negative,which suggested the stress factor for 2N survival.In the last part,we analyzed the transcriptomic data of livers from individuals with different ploidy of Lake Dianchi.The transcriptomic data of 2N/3N from Lake Erhai were used as control.The analyses including differential expression,shared-expressed genes and functional annotations for candidate genes were performed.The results showed that,1)in different positions of Lake Dianchi(Fushan and Dawan),the genes from both 2N and 3N in four biological processes(complement activation,lectin pathway,positive regulation of MAPK cascade,cytoskeleton organization and negative regulation of cell adhesion)were all differentially expressed;2)in different positions of Lake Dianchi(Fushan and Dawan),the expression of antioxidant genes(APOA1.TFPI)and anti-oncogene(VDAC1)were up-regulated,while the expression of proto-carcinoma(DIAPH3)and growth inhibition gene(IGFBP3)were down-regulated in 3N.This suggested the up-and down-regulated genes might promote the adaptation of 3N;further,we compared the expression of the same gene in individuals from Lake Dianchi and Erhai,and found the expression of genes in Lake Erhai were also up-regulated in 3N,but with significantly lower FPKM values comparing to the one from Lake Dianchi,this indicated the change of gene expression might be caused by the pollution instead of ploidy;3)there were 17 genes down-regulated in 3N from Fushan(with worse water quality),while they were up-regulated in Dawan(with relatively better quality of water),which indicated the changes might be due to the different levels of pollution.In summary,firstly,we developed two methods to distinguish 2N and 3N by theiri&morphological characteristics and found the machine learning are more efficiency and with higher accuracy rate;by analyzing the correlation between water quality and ploidy.Secondly,we identified the stress factors for 2N survival in pollution.Lastly,by digging the candidate genes related to the adaptations of pollution,we also found the potential resistance genes in 3N were signifieantly up-regulated,While the genes related to growth inhibiton and apoptosis were significantly down-regulated.The results suggested that 3N might be more adaptive in polluted Lake Dianchi than 2N as the promotion in expression of resistance genes.However,this results have not beenverified by experiment yet,more experimental evidences are still in need.Generally,the results in this study have provided basic clues for exploring the adaptation mechanisms and the similarities and differences between 3N and 2N in polluted Lake Dianchi.Using C.auratus complex as the research model,and the Lake Dianchi as a natural research lab,might help explore the myth of biological adaptability.Further studies would provide theoretic foundations for the biological protection and utilization of organisms in Lake Dianchi and worldwide for similar water pollution and recovery. |
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