Clam Meretrix lamarchii is delicious seafood with high economic value. The M. lamarchii in present market is mainly collected from wild population due to the lack of large-scale artificial seed production. In 2013,we ...Clam Meretrix lamarchii is delicious seafood with high economic value. The M. lamarchii in present market is mainly collected from wild population due to the lack of large-scale artificial seed production. In 2013,we carried out the artificial seedling exploration of M. Lamarchii. The current study utilized several statistical methods to analyze the effects of morphological traits on M. Lamarchii,which may provide knowledge for clam quality seedlings breeding work. The samples of M. Lamarchii were randomly sampled from Donghai Island,Zhanjiang. Shell length（ SL）,shell width（ SW）,shell height（ SH）,ligament length（ Li L）,lunule length（ Lu L） and total weight（ TW） of two-year-old M. Lamarchii were measured. A correlation coefficient matrix was constructed based on the results,where the total weight was set as the dependent variable and others as independent variables. Path coefficient and correlation index were calculated,and the major phenotypic characters were determined. The results showed that all the correlation coefficients between independent variables and dependent variable were significant（ P < 0. 01）,with an exception of the lunule length（ P > 0. 05）. The effects of the shell length,shell width,and shell height on the total weight were significant（ P < 0. 01）,and the shell length had dominant effect on the weight as a key effective factor. The multiple regression equation between the weight and the other traits was established as Y;=- 126. 784 + 1. 249X;+ 2. 036X;+ 0. 911 X;,where YWis total weight,X;,X;and X;are the shell length,shell width and shell height,respectively. The current study may contribute to the artificial breeding of the species.展开更多
Gene expression variation can be considered as a phenotype,and it plays an important role in both acclimation and adaption.However,genetic variation of gene expression received much less attention than traditional com...Gene expression variation can be considered as a phenotype,and it plays an important role in both acclimation and adaption.However,genetic variation of gene expression received much less attention than traditional commercial traits in aquaculture.To estimate the genetic variation and heritability of gene transcription in clam Meretrix petechialis,five Vibrio resistance-related genes were selected for gene expression analysis in the digestive gland,and an animal linear model was used to analyze data from quantitative real-time PCR(qRT-PCR).Among the five genes,BIRC7 showed significant additive genetic variations,the heritability of this gene of 12-month-and 15-month-old clams were 0.84±0.32 and 0.91±0.34,respectively.The heritability of other four genes(Bax,NFIL3,Big-Def,and CTL9)expression were low-tomoderate but not significantly expressed.Additionally,no significant phenotypic and genetic correlations between the BIRC7 transcription trait and body size were detected.This study highlights that certain gene expression variation is heritable and provides a reference for indirect selection of M.petechialis with high Vibrio resistance.展开更多
A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix（P1, P2 and P3） was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair ...A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix（P1, P2 and P3） was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair environments for growth traits. Analysis of variance for shell length and whole body weight indicated highly significant cross effects, environment effects and the interaction of cross by environment. General combining ability（GCA） and specific combing ability exhibited great variation among crosses and between two environments. Pooled over environments, P2 was the top combiner among the three parental families for both traits studied. The cross of P1 and P3 had the highest SCA. Additionally, significant reciprocal effects were observed. For individual environment, about half of the crossbred combinations showed favorable Mid-parent heterosis（MPH）（〉1%） for the shell length and whole body weight. Our data has shown that non-additive genetic and reciprocal effects constituted the major sources of genetic variation for both shell length and whole body weight, which indicates that crossbreeding among selective families could further explore the heterotic effects.展开更多
Disease in clams frequently occurred over the last decade and has become a serious threat to the clam aquaculture industry and natural stocks.Mass clam mortality events were reported to be associated with the presence...Disease in clams frequently occurred over the last decade and has become a serious threat to the clam aquaculture industry and natural stocks.Mass clam mortality events were reported to be associated with the presence of opportunistic pathogen vibrio.However,the complexity of infection that occurs in the natural environment remains poorly understood.In this study,we smulated a natural disease outbreak by vibrio immersion infection to study the diversity and dynamics of microbiota in the digestive tract of clam Meretrix petechialis during the infection process.Dramatic changes in operational taxonomic unit richness and phylum composition of the bacterial communities were observed during pathogen invasion.In addition,we investigated the potential relationship between microbiota dynamics and host status during disease progression.Results reveal that,at the end stage of vibrio infection,interindividual variation in the digestive tract microbiota increased,as did the diff erence in individual health status.The moribund clams displayed signs of microbial community shifts to low diversity,and the microbial community was characterized by mass proliferation of a few operational taxonomic units.展开更多
The precise and accurate knowledge of genetic parameters is a prerequisite for making efficient selection strategies in breeding programs.A number of estimators of heritability about important economic traits in many ...The precise and accurate knowledge of genetic parameters is a prerequisite for making efficient selection strategies in breeding programs.A number of estimators of heritability about important economic traits in many marine mollusks are available in the literature,however very few research have evaluated about the accuracy of genetic parameters estimated with different family structures.Thus,in the present study,the effect of parent sample size for estimating the precision of genetic parameters of four growth traits in clam M.meretrix by factorial designs were analyzed through restricted maximum likelihood（REML） and Bayesian.The results showed that the average estimated heritabilities of growth traits obtained from REML were 0.23-0.32 for 9 and 16 full-sib families and 0.19-0.22 for 25 full-sib families.When using Bayesian inference,the average estimated heritabilities were0.11-0.12 for 9 and 16 full-sib families and 0.13-0.16 for 25 full-sib families.Compared with REML,Bayesian got lower heritabilities,but still remained at a medium level.When the number of parents increased from 6 to 10,the estimated heritabilities were more closed to 0.20 in REML and 0.12 in Bayesian inference.Genetic correlations among traits were positive and high and had no significant difference between different sizes of designs.The accuracies of estimated breeding values from the 9 and 16 families were less precise than those from 25 families.Our results provide a basic genetic evaluation for growth traits and should be useful for the design and operation of a practical selective breeding program in the clam M.meretrix.展开更多
Hard clam(Meretrix meretrix)has a rich shell color variation among individuals from light yellow to bluish gray,brown red,and black,which may associating with melanin.Tyrosinase(Tyr)is a key rate-limiting enzyme for t...Hard clam(Meretrix meretrix)has a rich shell color variation among individuals from light yellow to bluish gray,brown red,and black,which may associating with melanin.Tyrosinase(Tyr)is a key rate-limiting enzyme for the biosynthesis of melanin,which affects the dark color of animal skin,hair,fur,scales and feathers.Here,we isolated and characterized the full-length cDNA sequence of M.meretrix tyrosinase gene(MmTyr)which encodes a protein with 689 amino acids.Sequence characteristics and phylogenetic analysis showed that there are a variety of Tyr genes in mollusks,which can be divided into different categories.The abundance of MmTyr transcript was detected in six tissues including mantle,adductor muscle,digestive gland,foot,gill and siphon of adult M.meretrix with qRT-PCR.The results showed a higher expression specifically in the mantle,digestive gland and siphon,which was consistent with the phenotypic color difference.In the embryos and larvae at different developmental stages,high expression was found in the trochophore larvae and juvenile clams.Among three M.meretrix strains with different shell colors,the expression level of MmTyr and total melanin content in the mantle edge both showed significant differences,suggesting that MmTyr is involved in the formation of shell color.The results obtained in this study will improve our understanding of molluscan tyrosinase gene function and molecular mechanism of shell color pattern determination.展开更多
A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selec- tion populations were generated with the shell color pattern as an additional selection criterion and named as ...A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selec- tion populations were generated with the shell color pattern as an additional selection criterion and named as SP （purple stripes） population and SB （black dots） population. The third-generation SP and SB popula- tions （08G3SP and 08G3SB, respectively） were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared. 08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms （p 〈 0.05）, yet 08G3SB individuals were significantly smaller than 08G3SP individ- uals at the nursery pond （p 〈 0.05）. Then, we examined the growth of the fourth-generation SP and SB populations （10G4SP and 10G4SB, respectively） at a commercial farm, and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams （p 〈 0.05） from May to September, when the water temperature was between 24.2-27.5℃, while 10G4SB lost the growth advantage in the other months. These results indicated that SP and SB populations responded differently to environmental factors, so it is beneficial for the clam farmers to select a suitable population according to the culture environment. Furthermore, a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis. However, the heterosis was not shown in this study, which might result from the slight genetic divergence between SB and SP populations.展开更多
The bioaccumulation and elimination rule of prometryn in hard clam Meretrix meretrix were studied under semistatic conditions. Whenthe water temperature was （12±1）℃, M. meretrix were exposed to the seawater co...The bioaccumulation and elimination rule of prometryn in hard clam Meretrix meretrix were studied under semistatic conditions. Whenthe water temperature was （12±1）℃, M. meretrix were exposed to the seawater containing 1, 10, and 100 μg/L prometryn. The content of prometrynin M. meretrix increased with the increase of exposed concentration, and both had significant positive correlation. The accumulation of prometryn inM. meretrix first increased then decreased, and finally fluctuated at a certain level. The maximum accumulation content was observed in M. meretrixwhen exposed to prometryn for 10, 14 and 18 d, and the maximum bioaccumulation factors （BCFs） were 22.9, 8.3 and 4.3, respectively. At the forthday of the elimination test, the content of prometryn in M. meretrix of each group were decreased above 50%. At the 22ndday of the elimination test,the content of prometryn in M. meretrix were decreased to 8.7%, 5.6% and 2.6% of the initial content in the elimination test, respectively. The results indicated that hard clam M. meretrix had strong bioaccumulation and elimination ability on prometryn.展开更多
Unbalanced parental contribution and small effective population size(N e)are common issues during the artifi cial breeding of marine bivalves.The impact of hatchery-spawning practices on parental contribution,effectiv...Unbalanced parental contribution and small effective population size(N e)are common issues during the artifi cial breeding of marine bivalves.The impact of hatchery-spawning practices on parental contribution,effective population size,the N e/N ratio,and genetic diversity are largely unknown.To address this,we conducted a parentage analysis on a complete 3×3 diallel cross of clam M eretrix meretrix using eight microsatellite markers.The genetic diversity of the parents was higher than that of their respective offspring in most crosses(8/9).Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross,and the same parent clam exhibited large variation in parental contribution among different crosses.The variance in male contribution was higher than that of the female contribution in most crosses,suggesting that male contribution was more skewed than for females.The N e/N ratio for nine crosses ranged from 0.58 to 0.86.There was no linear relationship between the sex ratio and the N e/N ratio(P>0.05).Moreover,a sex ratio closer to one-to-one does not necessarily mean a larger effective population size.A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio.展开更多
The effects on ethoxyresorufin O-deethylase （EROD）, NADPH-cytochrome c reductase and NADH cytochrorne b5 reductase activities of digestive gland in Meretrix meretrix exposed to tributyltin （TBT） at environmental l...The effects on ethoxyresorufin O-deethylase （EROD）, NADPH-cytochrome c reductase and NADH cytochrorne b5 reductase activities of digestive gland in Meretrix meretrix exposed to tributyltin （TBT） at environmental levels （0.1,1.0,10.0 ng/dm as stannum concentration）,in experimental condition, were evaluated. The EROD, NADH cytochrorne b5 reductase activities were significantly inhibited after exposure to 10.0 ng/dm^3 TBT for 8 and 20 d, the NADPH cytochrorne c reductase activities were significantly inhibited after exposure to 0.1,1.0 and 10.0 ng/dm TBT for 8 d and to 1.0 and 10.0 ng/dm for 20 d, as compared with the matched control, while NADH cytochrorne b5 reductases and NADPH cytochrome c reductase activities were induced after exposure to 10.0 ng/dm^3 TBT for 2 d. The EROD activity in the 10 ng/dm^3 group,and the NADH cytochrome b5 reductases activities in 1.0 and 10.0 ng/dm groups, were significantly induced when transferred to clean recovery tanks for 7 d. The three enzymic activities in the clams exposed to TBT were recovered to the level corresponding to that of the control group after transfer to clean recovery tanks for 20 d. NADPH cytochrome c reductase activity in Meretrix meretrix seems to be more sensitive to exposure of TBT than that of the EROD and NADH cytochrome b5 reductases. The results suggest that induction and inhibition by TBT to the monooxygenase system enzymic activity in Meretrix meretrix would simultaneously exist. The enzymic activities were inhibited by exposure for a long time. The results suggest that inhibition of the monooxygenase system should be an indication of the exposure to environmentally relevant concentrations of TBT for a long time.展开更多
文摘Clam Meretrix lamarchii is delicious seafood with high economic value. The M. lamarchii in present market is mainly collected from wild population due to the lack of large-scale artificial seed production. In 2013,we carried out the artificial seedling exploration of M. Lamarchii. The current study utilized several statistical methods to analyze the effects of morphological traits on M. Lamarchii,which may provide knowledge for clam quality seedlings breeding work. The samples of M. Lamarchii were randomly sampled from Donghai Island,Zhanjiang. Shell length（ SL）,shell width（ SW）,shell height（ SH）,ligament length（ Li L）,lunule length（ Lu L） and total weight（ TW） of two-year-old M. Lamarchii were measured. A correlation coefficient matrix was constructed based on the results,where the total weight was set as the dependent variable and others as independent variables. Path coefficient and correlation index were calculated,and the major phenotypic characters were determined. The results showed that all the correlation coefficients between independent variables and dependent variable were significant（ P < 0. 01）,with an exception of the lunule length（ P > 0. 05）. The effects of the shell length,shell width,and shell height on the total weight were significant（ P < 0. 01）,and the shell length had dominant effect on the weight as a key effective factor. The multiple regression equation between the weight and the other traits was established as Y;=- 126. 784 + 1. 249X;+ 2. 036X;+ 0. 911 X;,where YWis total weight,X;,X;and X;are the shell length,shell width and shell height,respectively. The current study may contribute to the artificial breeding of the species.
基金Supported by the China Agriculture Research System(No.CARS-49)the National Natural Science Foundation of China(No.31772845)+1 种基金the Science and Technology Service Network Initiative of the Chinese Academy of Sciences(No.KFJ-STS-ZDTP-049)the Foundation of Zhejiang Key Laboratory of Exploitation and Preservation of Coastal Bio-Resource(No.J2018001)
文摘Gene expression variation can be considered as a phenotype,and it plays an important role in both acclimation and adaption.However,genetic variation of gene expression received much less attention than traditional commercial traits in aquaculture.To estimate the genetic variation and heritability of gene transcription in clam Meretrix petechialis,five Vibrio resistance-related genes were selected for gene expression analysis in the digestive gland,and an animal linear model was used to analyze data from quantitative real-time PCR(qRT-PCR).Among the five genes,BIRC7 showed significant additive genetic variations,the heritability of this gene of 12-month-and 15-month-old clams were 0.84±0.32 and 0.91±0.34,respectively.The heritability of other four genes(Bax,NFIL3,Big-Def,and CTL9)expression were low-tomoderate but not significantly expressed.Additionally,no significant phenotypic and genetic correlations between the BIRC7 transcription trait and body size were detected.This study highlights that certain gene expression variation is heritable and provides a reference for indirect selection of M.petechialis with high Vibrio resistance.
基金Supported by the National Special Research Fund for Non-Profit Marine Sector(No.201305043)the Key Laboratory for Ecological Environment in Coastal Areas,State Oceanic Administration(No.201311)+1 种基金the Collaborative Innovation Center for Zhejiang Marine High-Efficiency and Healthy Aquaculturethe K.C.Wong Magna Fund at Ningbo University
基金The National High-Tech R&D Program of China(863 Program)under contract No.2012AA10A410the Key Technologies R&D Program of Jiangsu Province under contract No.BE2011372
文摘A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix（P1, P2 and P3） was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair environments for growth traits. Analysis of variance for shell length and whole body weight indicated highly significant cross effects, environment effects and the interaction of cross by environment. General combining ability（GCA） and specific combing ability exhibited great variation among crosses and between two environments. Pooled over environments, P2 was the top combiner among the three parental families for both traits studied. The cross of P1 and P3 had the highest SCA. Additionally, significant reciprocal effects were observed. For individual environment, about half of the crossbred combinations showed favorable Mid-parent heterosis（MPH）（〉1%） for the shell length and whole body weight. Our data has shown that non-additive genetic and reciprocal effects constituted the major sources of genetic variation for both shell length and whole body weight, which indicates that crossbreeding among selective families could further explore the heterotic effects.
基金Supported by the National Natural Science Foundation of China(No.31772845)the China Agriculture Research System(No.CARS-49)+1 种基金the Science and Technology Service Network Initiative of the Chinese Academy of Sciences(No.KFJ-STS-ZDTP-049)the Foundation of Zhejiang Key Laboratory of Exploitation and Preservation of Coastal Bio-Resource(No.J2018001)。
文摘Disease in clams frequently occurred over the last decade and has become a serious threat to the clam aquaculture industry and natural stocks.Mass clam mortality events were reported to be associated with the presence of opportunistic pathogen vibrio.However,the complexity of infection that occurs in the natural environment remains poorly understood.In this study,we smulated a natural disease outbreak by vibrio immersion infection to study the diversity and dynamics of microbiota in the digestive tract of clam Meretrix petechialis during the infection process.Dramatic changes in operational taxonomic unit richness and phylum composition of the bacterial communities were observed during pathogen invasion.In addition,we investigated the potential relationship between microbiota dynamics and host status during disease progression.Results reveal that,at the end stage of vibrio infection,interindividual variation in the digestive tract microbiota increased,as did the diff erence in individual health status.The moribund clams displayed signs of microbial community shifts to low diversity,and the microbial community was characterized by mass proliferation of a few operational taxonomic units.
基金The National High Technology Research and Development Program(863 program)of China under contract No.2012AA10A410the Zhejiang Science and Technology Project of Agricultural Breeding under contract No.2012C12907-4the Scientific and Technological Innovation Project financially supported by Qingdao National Laboratory for Marine Science and Technology under contract No.2015ASKJ02
文摘The precise and accurate knowledge of genetic parameters is a prerequisite for making efficient selection strategies in breeding programs.A number of estimators of heritability about important economic traits in many marine mollusks are available in the literature,however very few research have evaluated about the accuracy of genetic parameters estimated with different family structures.Thus,in the present study,the effect of parent sample size for estimating the precision of genetic parameters of four growth traits in clam M.meretrix by factorial designs were analyzed through restricted maximum likelihood（REML） and Bayesian.The results showed that the average estimated heritabilities of growth traits obtained from REML were 0.23-0.32 for 9 and 16 full-sib families and 0.19-0.22 for 25 full-sib families.When using Bayesian inference,the average estimated heritabilities were0.11-0.12 for 9 and 16 full-sib families and 0.13-0.16 for 25 full-sib families.Compared with REML,Bayesian got lower heritabilities,but still remained at a medium level.When the number of parents increased from 6 to 10,the estimated heritabilities were more closed to 0.20 in REML and 0.12 in Bayesian inference.Genetic correlations among traits were positive and high and had no significant difference between different sizes of designs.The accuracies of estimated breeding values from the 9 and 16 families were less precise than those from 25 families.Our results provide a basic genetic evaluation for growth traits and should be useful for the design and operation of a practical selective breeding program in the clam M.meretrix.
基金supported financially by the National Key Research and Development Program of China (No. 2018YFD0901404)the National Natural Science Foundation of China (No. 31772846)+3 种基金the Zhejiang Provincial Natural Science Foundation (No. LY16C190004)the General project of Zhejiang Provincial Educational Department (No. Y201329410)the Open-End Funds of Jiangsu Key Laboratory of Marine Biotechnology (No. HS16001)the Modern Agro-Industry Technology Research System (No. CARS-49)
文摘Hard clam(Meretrix meretrix)has a rich shell color variation among individuals from light yellow to bluish gray,brown red,and black,which may associating with melanin.Tyrosinase(Tyr)is a key rate-limiting enzyme for the biosynthesis of melanin,which affects the dark color of animal skin,hair,fur,scales and feathers.Here,we isolated and characterized the full-length cDNA sequence of M.meretrix tyrosinase gene(MmTyr)which encodes a protein with 689 amino acids.Sequence characteristics and phylogenetic analysis showed that there are a variety of Tyr genes in mollusks,which can be divided into different categories.The abundance of MmTyr transcript was detected in six tissues including mantle,adductor muscle,digestive gland,foot,gill and siphon of adult M.meretrix with qRT-PCR.The results showed a higher expression specifically in the mantle,digestive gland and siphon,which was consistent with the phenotypic color difference.In the embryos and larvae at different developmental stages,high expression was found in the trochophore larvae and juvenile clams.Among three M.meretrix strains with different shell colors,the expression level of MmTyr and total melanin content in the mantle edge both showed significant differences,suggesting that MmTyr is involved in the formation of shell color.The results obtained in this study will improve our understanding of molluscan tyrosinase gene function and molecular mechanism of shell color pattern determination.
基金The National High Technology Research and Development Program of China (863 Program) under contract No.2012AA10A410National S&T Support Program under contract No.2011BAD13B09the Key Technologies R&D Program of Jiangsu under contract No.BE2011372
文摘A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selec- tion populations were generated with the shell color pattern as an additional selection criterion and named as SP （purple stripes） population and SB （black dots） population. The third-generation SP and SB popula- tions （08G3SP and 08G3SB, respectively） were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared. 08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms （p 〈 0.05）, yet 08G3SB individuals were significantly smaller than 08G3SP individ- uals at the nursery pond （p 〈 0.05）. Then, we examined the growth of the fourth-generation SP and SB populations （10G4SP and 10G4SB, respectively） at a commercial farm, and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams （p 〈 0.05） from May to September, when the water temperature was between 24.2-27.5℃, while 10G4SB lost the growth advantage in the other months. These results indicated that SP and SB populations responded differently to environmental factors, so it is beneficial for the clam farmers to select a suitable population according to the culture environment. Furthermore, a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis. However, the heterosis was not shown in this study, which might result from the slight genetic divergence between SB and SP populations.
基金Supported by Science and Technology Plan of Nanjing Customs(Former Jiangsu Inspection and Quarantine Bureau)(2017KJ12)
文摘The bioaccumulation and elimination rule of prometryn in hard clam Meretrix meretrix were studied under semistatic conditions. Whenthe water temperature was （12±1）℃, M. meretrix were exposed to the seawater containing 1, 10, and 100 μg/L prometryn. The content of prometrynin M. meretrix increased with the increase of exposed concentration, and both had significant positive correlation. The accumulation of prometryn inM. meretrix first increased then decreased, and finally fluctuated at a certain level. The maximum accumulation content was observed in M. meretrixwhen exposed to prometryn for 10, 14 and 18 d, and the maximum bioaccumulation factors （BCFs） were 22.9, 8.3 and 4.3, respectively. At the forthday of the elimination test, the content of prometryn in M. meretrix of each group were decreased above 50%. At the 22ndday of the elimination test,the content of prometryn in M. meretrix were decreased to 8.7%, 5.6% and 2.6% of the initial content in the elimination test, respectively. The results indicated that hard clam M. meretrix had strong bioaccumulation and elimination ability on prometryn.
基金Supported by the National High Technology Research and Development Program of China(863 Program)(No.2012AA10A410)the Key Technology R&D Program of Jiangsu Province,China(No.BE2011372)
文摘Unbalanced parental contribution and small effective population size(N e)are common issues during the artifi cial breeding of marine bivalves.The impact of hatchery-spawning practices on parental contribution,effective population size,the N e/N ratio,and genetic diversity are largely unknown.To address this,we conducted a parentage analysis on a complete 3×3 diallel cross of clam M eretrix meretrix using eight microsatellite markers.The genetic diversity of the parents was higher than that of their respective offspring in most crosses(8/9).Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross,and the same parent clam exhibited large variation in parental contribution among different crosses.The variance in male contribution was higher than that of the female contribution in most crosses,suggesting that male contribution was more skewed than for females.The N e/N ratio for nine crosses ranged from 0.58 to 0.86.There was no linear relationship between the sex ratio and the N e/N ratio(P>0.05).Moreover,a sex ratio closer to one-to-one does not necessarily mean a larger effective population size.A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio.
文摘The effects on ethoxyresorufin O-deethylase （EROD）, NADPH-cytochrome c reductase and NADH cytochrorne b5 reductase activities of digestive gland in Meretrix meretrix exposed to tributyltin （TBT） at environmental levels （0.1,1.0,10.0 ng/dm as stannum concentration）,in experimental condition, were evaluated. The EROD, NADH cytochrorne b5 reductase activities were significantly inhibited after exposure to 10.0 ng/dm^3 TBT for 8 and 20 d, the NADPH cytochrorne c reductase activities were significantly inhibited after exposure to 0.1,1.0 and 10.0 ng/dm TBT for 8 d and to 1.0 and 10.0 ng/dm for 20 d, as compared with the matched control, while NADH cytochrorne b5 reductases and NADPH cytochrome c reductase activities were induced after exposure to 10.0 ng/dm^3 TBT for 2 d. The EROD activity in the 10 ng/dm^3 group,and the NADH cytochrome b5 reductases activities in 1.0 and 10.0 ng/dm groups, were significantly induced when transferred to clean recovery tanks for 7 d. The three enzymic activities in the clams exposed to TBT were recovered to the level corresponding to that of the control group after transfer to clean recovery tanks for 20 d. NADPH cytochrome c reductase activity in Meretrix meretrix seems to be more sensitive to exposure of TBT than that of the EROD and NADH cytochrome b5 reductases. The results suggest that induction and inhibition by TBT to the monooxygenase system enzymic activity in Meretrix meretrix would simultaneously exist. The enzymic activities were inhibited by exposure for a long time. The results suggest that inhibition of the monooxygenase system should be an indication of the exposure to environmentally relevant concentrations of TBT for a long time.
