| Manila clam Ruditapes philippinarum widely distribute in different sea area,it is a kind of commercially important marine shellfish in China.Its shell shape has complex and abundant polymorphism.This study intended to investigate genetic differentiation and difference degree of shell shape among different geographical populations of Ruditapes philippinarum with morphological analysis method;Simultaneously compared commercial traits of Ruditapes philippinarum among different populations,then revealed relationship,influence effect,and determinant connection between shell traits and volume;finally used design of 2×2 complete diallel hybrid to analyse herterosis of offspring among different crossbred groups.1.Analysis of shell shape among different populations of Ruditapes philippinarumBased on seven shell index of populations of Ruditapes philinppinarum from Japan(RB),North Korea(CX),Dalian(DL),Huludao(HLD),Jinzhou Banma(BM),multivariate statistical analysis were conducted on analysis of differentiation of shell shape among different populations of Ruditapes philinppinarum.(1)According to descriptor of shell shape,Ruditapes philippinarum within North Korea and Huludao were characterized by relatively round shells(shell height/shell length=0.7335,Circle index lateral view=0.5414;shell height/shell length=0.7096,Circle index lateral view=0.5865),Ruditapes philippinarum within Dalian were characterized by plump or globular shape(shell width/shell length=0.4873,Reference Ellipse index ventral view=0.7381),So the shell of the Dalian population is the most "full",close to the round ball.(2)Contributory ratios of the first two principal components within principal components analysis were 53.36% and 24.09% respectively,the cumulative contribu-tory ratio was 77.45%.Scatter plot further indicated that small part of the Banma's and most of Huludao's Ruditapes philippinarum almost had no overlap area with other populations of Ruditapes philippinarum.Most of the Dalian and North Korea groups have overlapping areas,and there are also some intersecting phenomena in Japan,Dalian and zebra groups.(3)The results of cluster analysis showed that the populations of Ruditapes philippinarum from Japan and Banma were closest in morphology.The shell shape of North Korea and Dalian population were also rather similar,they could gather together with Huludao population.(4)The integrated discriminant accuracy was 76.8%,the highest discriminant accuracy presented in zebra population(88%),and the lowest accuracy presented in North Korea population(58%).Based on scatter diagram of the first two discriminant functions,the results of discriminant analysis and principal components analysis were basically consistent.2.Comparison of growing traits among different geographical populations of Ruditapes philippinarumThe purpose of this study was to investigate variations in quantitative traits among different geographical populations of Ruditapes philippinarum,compared weight traits(live weight,soft weight,shell weight),volume(total volume,shell volume,shell cavity volume),and meat rate by ANOVA analysis.The results showed that there were significantly differences in live weight and shell weight between Dalian and other populations(p<0.05),significantly differences also existed in soft weight between Banma and other populations.About volume,total volume,shell volume and shell cavity volume of Dalian population were bigger than other populations significantly(p<0.05),Meat rate was in the following order: BM>HLD>RB>DL>CX.Correlation analysis and pathway analysis were applied in discussion about relatonship and influence effect between shell traits and volume among five populations of Ruditapes philippinarum.Then regression equations of shell traits on volume were established by stepwise regression analysis.There were significant correlation coefficient between shell traits and volume among different populations(p<0.01);Shell traits had different direct contributions to volume among different populations.As to total volume,the shell length was the major direct factor in total volume in the populations from Banma(0.78969),as to shell cavity volume,the shell width was the biggest direct influence to shell cavity volume in Japan(0.89483),while as to shell volume,the direct effect of shell height on shell volume was the great one in Dalian(0.66592);There were some differences in the regression equation of shell traits to volume among different populations.3.Early growth of hybrid among different shell shape strains of Ruditapes philippinarumAccording to 2 ratios of shell width and shell length,divided wild Ruditapes philippinarum from Laizhou into two strains.A 2×2 complete diallel cross was investigated using three strains of Ruditapes philippinarum,wide-shell(W)and plate-shell(P),Growth of Shell length and heterosis during different larval and juvenile stages were compared among two parental groups and four reciprocal hybrid crosse.The results indicated that cross PW was the only one that showed weak superiority of growth at larval stages,and average value of growing superiority was 2.46.Cross WP had the better heterosis for juvenile shell length than others,which reached 6.35.In the extended index,the PW experimental group showed a weak advantage in larval stage,with an average of 1.37.The elongation index of WP group was the most obvious and the advantage average value was 4.88.There were different heterosis among six reciprocal hybrid crosses,it might be attributed to genetic,environmental and maternal effects. |
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