Genetic Studies Of Quantitative Traits And Shell Colors In Two Hatchery Stocks Of The Bay Scallop, Argopecten Irradians Irradians

The bay scallop Argopecten irradians is distributed discontinously along the Atlantic and Gulf of the United States, including four subspecies: A i. irradians (Lamarck), A. i. concentricus (Say), A. i.amplicostatus (Dall), and A i. taylorae (Petuch). Various shell colors including gray, brown, yellow, orange, purple, and white are found at four subspecies. In 1982, the northern subspecies, A. i. irradians, was first introduced into China successfully from the U.S. A. and developed into one of the most important cultured bivalves in China rapidly. 406 individuals of the subspecies were reintroduced into China in December 1998 and February 1999 from U.SA., and they have become the most important culture stock currently. Each might present potentially different genetic resources, therefore, different stocks provide very useful materials for genetic improvement and breeding of the animal. Quantitative traits for Stock A (their ancestor was introduced in 1982) and Stock B (their ancestor was introduced in 1998 and 1999) have been studied by various lines since the beginning of 2002, including responses to selection, realized heritability, inbreeding depression, heterosis, and interaction between genotype and environment Meanwhile, genetics of various shell colors of Stock B has also been studied. The major results and conclusions are as follows:1 Response to selection and realized heritability1.1 For Stock A, response to selection and realized heritability were very small (0.077±0.058 and 0.045±0.034, respectively).1.2 For Stock B, responses to selection and realized heritability were 0.650±0.139 and 0.397+0.085 for the first generation, and they were 0.612±0.101 and 0.349+0.057 for the second generation. Genetic gain for the first and the second generation were 10.2% and 10.6%, and the total genetic gain for two generations was up to 17.56%. Retained genetic gain after the first generation selection was 6.25%.1.3 Afterone generation of divergent selection, responses to selection and realized heritability were 0.358 ± 0.082 and 0.208 ± 0.047 for a self-fertilized line derived from Stock A, and they were 0.403±0.141 and0.232±0.081 forafull-sib line derived from Stock B.2 Inbreeding depression2.1 After one self-fertilization generation, the magnitude of inbreeding depression for Stock A was 8.70%, which was significantly smaller than 17.72% for Stock B.2.2 Inbreeding of Stock A was nearly no longer depressed after three self-fertilization generations, whereas inbreeding depression was still up to 12.91% after two generations of self-fertilization for Stock B.2.3 The magnitude of inbreeding depression caused by self-fertilization was different for different progeny derived from various mating systems (random mating, full-sib, and self-fertilization), which were 21.53%, 14.64% and 10.11%, respectively. Inbreeding depression rates decreased with inbreeding coefficient increasing.3 Heterosis3.1 For crosses between two stocks A and B, mid-parent heterosis was smaller than single-parent heterosis of Stock A, but bigger than single-parent heterosis of Stock B, which was 7.81%, 22.98%, and -4.02%, respectively.3.2 For crosses between two lines A and B, mid-parent heterosis was smaller than Line A single-parent heterosis, but bigger than single-parent heterosis of Line B, which was 4.27%, 9.80%, and, -0.61%, respectively.4 Interaction between genotype and environment4.1 Both survival and growth of larvae were significantly different not only among upward-, downward-, and non-selected groups under the same temperature or salinity conditions, but also among three temperatures or salinities for anyone of the three larvae groups.4.2 Both inbreeding depression and heterosis were changed with the changing of environmental conditions.5 Genetics of shell color5.1 Different shell color might be controlled by different gene.5.2 Orange, purple, and white might be controlled by one gene; orange-purple, brown, and black might be controlled by more than three genes.5.3 There might be simple dominant-recessive relation...