Edouard Bedier

Microsatellite-associated heterosis in hatchery-propagated stocks of the shrimp Penaeus stylirostris

Abstract Correlation between DNA microsatellite heterozygosity and growth rate was investigated in two hatchery-propagated stocks of the shrimp Penaeus stylirostris, which had been genetically isolated from wild founders for 17 generations, and from each other for five more generations. Presumed demographic history of these populations suggested that they were maintained at small effective population sizes, and this was confirmed by significant changes in allelic frequencies between the two stocks. Despite a small sample size (n=60) and a small number of loci screened, a significant positive correlation was detected between microsatellite tri-locus heterozygosity and growth rate in one of the two stocks (r=0.3, P=0.02). In the other stock (n=48), the positive correlation was not significant, but the combined test of single locus heterozygote advantage over the three loci was significant (P=0.005). Use of DNA microsatellite markers, whose selectively neutral status is generally accepted, allowed us to reject the hypothesis of direct overdominance at marker loci as an explanation for an association of growth rate with heterozygosity. The average depression associated with one locus in our case is above or equivalent to the amount observed for a 10% increase of inbreeding in other species. These results suggest that heterozygosity at neutral marker loci is sufficiently well correlated with individual inbreeding coefficients to reveal a significant residual inbreeding load for growth rate in Tahitian P. stylirostris stocks. Inbreeding during hatchery propagation was, thus, insufficient to purge the ancestral load.

Selection for better growth of Penaeus stylirostris in Tahiti and New Caledonia

Abstract The penaeid shrimp, Penaeus stylirostris , has been domesticated in French Polynesia and New Caledonia for 20 years and was used in an experimental mass selection for better growth. The population under selection was graded once or twice each generation, which induced a selection rate fluctuating between 4% and 18% from 1 year to the next. At each generation, 24 to 32 individuals were used as parents (Ne=21–32) in the selected line and in the control line. The injection of colored elastomer in the two populations allowed an assessment of the genetic progress in earthen rearing ponds. The fifth generation demonstrated an increase of growth rate of 21% when compared to the nonselected control line. The optimization of the selection schemes and their integration into the production hatcheries is discussed with a special focus on the optimization of the age of grading.

Screening for intron-length polymorphisms in penaeid shrimps using exon-primed intron-crossing (EPIC)-PCR.

Keywords: cross-species amplification; EPIC-PCR; intron-length polymorphism; Penaeus japonicus; Penaeus monodon; Penaeus vannamei