| Litopenaeus vannamei,commonly known as South American white shrimp,is native to the Pacific coast of Central and South America.It was introduced into China at the end of the 20 th century.After more than 30 years of development,it has become one of the most important economic aquaculture varieties in China.Due to its characteristics of fast growth,delicious meat and strong resistance to stress,its cultivation economic benefit is remarkable,and Fenneropenaeus chinensis and Penaeus Monodon are listed as the world’s three largest cultured shrimp species.Litopenaeus vannamei belongs to poitherm and is highly dependent on ambient temperature,so it is easily affected by external temperature.The change of temperature can directly affect the growth,reproduction,development,metabolism,feeding and even survival of Litopenaeus vannamei.Therefore,temperature is a non-negligible environmental factor in the culture process of Litopenaeus vannamei.The optimum water temperature for the growth,survival and feeding of Litopenaeus vannamei is 18-35℃.When the water temperature reached 35℃ to 40℃,the growth and feeding of Litopenaeus vannamei would be affected to a certain extent.When the water temperature reached 40℃,all Litopenaeus vannamei died within a certain period of time.In recent years,the impact of global warming is gradually significant,with frequent extreme weather,and the duration of high temperature in summer has also increased significantly.Moreover,in the summer of south China,the direct sunlight causes the water temperature to be too high,which has a certain impact on the cultivation of Litopenaeus vannamei.However,the high temperature tolerance of Litopenaeus vannamei is not known at present.In this study,we used Litopenaeus vannamei as experimental materials to conduct the experiment of high temperature stress by artificial heating method.On the one hand,we explored the differences of high temperature tolerance traits among Litopenaeus vannamei families and strains,and evaluated the genetic parameters of high temperature tolerance traits of Litopenaeus vannamei.Therefore,it provides a theoretical basis for formulating a reasonable and effective breeding program for high-temperature tolerance traits of Litopenaeus vannamei.On the other hand,in the use of the transcriptome sequencing technology,measurement of room temperature group(28 ℃)and high temperature stress group(40 ℃),achieved the whole shrimp sequencing,screening differentially expressed genes under high temperature stress and temperature related metabolic pathways,to predict and discovery,achieved high temperature resistance of new genes and prawn high-temperature resistance screening of molecular markers to lay a good foundation.The main results of this study are as follows:1.Analysis of high temperature tolerance of different strains of Litopenaeus vannameiIn order to understand the high-temperature resistance traits of Litopenaeus vannamei and explore the differences of high-temperature resistance traits among families and strains,12 families of Litopenaeus vannamei with high resistance and precocity strain were selected to conduct high-temperature stress experiments,and the heat resistance values of Litopenaeus vannamei families were calculated according to the UTT of high-temperature resistance traits.The results showed that the average heat resistance of the 24 Litopenaeus vannaei families ranged from 1000.1 to 1283.18℃·h,and that of the high resistance families ranged from 1000.1 to 1262.44℃·h,and that of the early maturity families ranged from 1017.57 to 1283.18℃·h.There were significant differences in heat resistance values among different lines,and the F test reached a significant level(P < 0.05).There was little difference in heat resistance between high resistance and early maturity strains,and F test did not reach a significant level(P >0.05).There were significant differences in high-temperature tolerance of high resistance and early maturity strains at family level(P < 0.05),but no significant differences at strain level(P > 0.05).2.Heritability analysis of high temperature tolerance of juvenile Litopenaeus vannameiIn order to study the effects of high temperature on the genetic variation of Litopenaeus vannamei,40 full-sibling families were randomly selected from the 4Litopenaeus vannamei populations(EGDB,PRMA,API,SIS)that were introduced from abroad in 2018,and 100 individuals were randomly selected from each family,which were divided into two parts and put into the designated experimental barrel.A total of 4000 larvae.Using water bath heating method,the experimental barrel was heated and its corresponding survival time and temperature were recorded.A single character animal model was used to evaluate the genetic parameters of high temperature tolerance.The results showed that the heat resistance of larvae of Litopenaeus vannamei ranged from 782.64 to 2074.33℃·h,among which there were 5 families(10401,10364,10345,10361 and 10359)with heat resistance higher than 1800℃·h,and 5 families(10401,10364,10345,10361 and 10359)with heat resistance lower than900℃·h.10480,10462,10434,10417,10414.The heritability of high-temperature tolerance in juvenile Litopenaeus vannamei was estimated to be 0.22±0.053 by using a single character animal model combined with pedigree information,which was medium heritability.The results indicated that the high temperature tolerance traits of juvenile Litopenaeus vannamei had a high level of genetic variation and a great potential for genetic improvement.3.Gene expression differences of Litopenaeus vannamei under heat stressIn order to study the gene response of Litopenaeus vannamei under normal temperature and high temperature stress,24 Litopenaeus vannamei families were tested under high temperature stress,and 3 Litopenaeus vannamei families with high heat resistance values were selected.Transcriptome sequencing was used to analyze the transcriptional levels of three Litopenaeus vannamei families under the conditions of control(28℃)and heat stress(40℃).The results showed that a total of 84,7249,496 original data were measured from 18 samples of 3 Litopenaeus vannamei families.After filtering the original data,a total of 79,763,608 clean reads and 119.65 G Clean＿bases were obtained.2631,5220 and 2824 differentially expressed genes were screened from4439,5001 and 5002 families,respectively,among which 68 differentially expressed genes were common in the three families.In GO enrichment analysis,the differential genes were significantly concentrated in chitin metabolism,aminoglycan metabolism,glucosamine compound metabolism,aminoglycan metabolism,extracellular domain,and chitin binding.In KEGG enrichment analysis,the differential genes were significantly concentrated in glycine,serine and threonine metabolic pathways,life span regulation pathways,glycolysis/gluconeogenesis pathways,endoplasmic reticulum protein processing,and amino acid biosynthesis pathways. |
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