| Macrobrachium rosenbergii originates from tropical and subtropical regions.Low temperatures limit its culturing time and area in China.Therefore,cultivating new varieties with high quality,high yield and low temperature tolerance is conducive to breaking through the time and space constraints of their culturing and improving economic benefits.The basic theoretical research on genetic parameter analysis and related gene screening of cold-tolerant traits can provide reference for the breeding of new cold-tolerant varieties.In this study,a linear mixed model was developed by artificially cooling a population of adult M.rosenbergii indoors,and the genetic parameters of cold-tolerance traits（Cooling degree hours,CDH）and growth traits（Body weight,BW;Body length,BL）were assessed by ASReml-R based on the restricted maximum likelihood method for a culture duration of about 200 days.Body weight（BW）and body length（BL）were evaluated by ASReml-R,and multiple regression analysis and path analysis were performed for the cold tolerance traits（CDH）and growth traits（BW）of adult M.rosenbergii using SPSS software.At the same time,in order to further explore the molecular mechanism of low temperature tolerance of M.rosenbergii,the juvenile M.rosenbergii cultured for about 80 days was selected for Cold stress experiment,and the hepatopancreas and muscle of cold-sensitive group（CS）and the cold-tolerant group（CT）under low temperature stress and the control group were subjected to transcriptome analysis.The main research results are as follows:1.The heritability of the cold tolerance trait（CDH）in adult M.rosenbergii cultured for about 200 days was low（0.12±0.05）,which reached a significant level by statistical test（P<0.05）;the heritability of the growth traits BW and BL was medium-low（0.2±0.06,0.1±0.04）,which also reached a significant level by statistical test（P<0.05）,and the heritability of BW was higher than that of BL,and the coefficient of variation of BW was larger,indicating that BW has a greater potential for genetic improvement.2.The phenotypic and genetic correlation coefficients between the growth traits BW and BL of adult M.rosenbergii were 0.66±0.019 and 0.78±0.085,respectively,showing a highly significant positive correlation（P<0.05）,suggesting that selection for breeding with one of BW and BL as the target trait can have a synergistic effect on the other trait.The phenotypic and genetic correlations of CDH vs.BW,and CDH vs.BL were-0.21±0.033 and-0.71±0.127,-0.63±0.022 and-0.94±0.034,respectively,all of which were highly significant negative correlations（P<0.05）,subsequently suggesting that CDH,BW,and BL are difficult to achieve simultaneous improvement of the two traits including low temperature tolerance and growth in the same population.3.When the mean BW of adult M.rosenbergii was 50.63±17.99 g and the mean BL was 128.15±21.33 mm,the low temperature tolerance of adult M.rosenbergii that were carrying eggs was significantly greater than that of prawn that had carried eggs and never carried eggs;M.rosenbergii in the hard-shelled group tolerated cold temperatures better than the soft-shelled group;the cold tolerance of the group with chela was stronger than that of the group without chela;sex did not affect the CDH of adult M.rosenbergii,but the low-temperature mortality temperature of male was higher than that of female prawn.It is suggested that the hard-shelled and chelated prawn should be retained as parents in the selection and breeding of cold-tolerant varieties of M.rosenbergii.The main factors affecting CDH may be other than the six phenotypic traits of egg-carrying status,exoskeleton hardness,body length,number of dorsal rostrum teeth,number of ventral rostrum teeth,and abdominal weight.Therefore,the future studies need to increase the measured indices and establish a more complete model.In addition,direct selection for adult M.rosenbergii for body length,length of second leg,carapace length,abdominal length,number of dorsal rostrum teeth,weight of second leg,and abdominal weight traits can be achieved by indirect selection for BW.4.The initial mortality temperature was about 16.5±0.5℃,the temperatures resulting in lowest LT50（lethal temperature at which 50% prawn die）and lowest lethal temperature were approximately 12.5±0.5℃ and 11.5±0.5℃ when juvenile M.rosenbergii was respectively 1.87±0.86 g in body weight and the mean BL was41.87±5.45 mm in body length after culturing about 80 days.The exoskeletal hardness of juvenile M.rosenbergii does not affect their cold-tolerance ability;When M.rosenbergii was in the juvenile stage,the more cold-tolerant the juvenile prawn BW>2g was,the stronger the cold-tolerance of CT than CS group.5.There were 10 differentially expressed genes（DEGs）（P<0.05）,including acetylCoA carboxylase,transcription factor ATF-b and heat shock protein 90,that played important roles in the low temperature stress response in M.rosenbergii.The hepatopancreas had more DEGs than muscle,and several pathways were activated in the hepatopancreas,including folate biosynthesis,starch and sucrose metabolism,and pancreatic secretion,suggesting that this tissue may play a key role in response to low temperature stress.Among these pathways,folate biosynthesis is overlapping to both hepatopancreas and muscle,and this pathway may affect the immune system and antioxidant capacity of M.rosenbergii during low temperature stress.The only upregulated gene in this pathway was Alkaline phosphatase,indicating that this gene may play a key role in the low-temperature response.It can be seen that the cold tolerance traits（CDH）and growth traits of adult M.rosenbergii are difficult to achieve selection in the same population at the same time;the exoskeletal hardness,egg-carrying status and claw number of adult prawns can affect their cold tolerance ability.The low-temperature tolerance of juvenile R.rosenbergii was affected by BW,but not by exoskeletal hardness;the hepatopancreas of juvenile prawn is a key tissue for low-temperature response,and Alkaline phosphatase may be the main pathway for low-temperature stress in juvenile prawn. |
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