Genetics of the resistance to hypoxia in postlarvae and juveniles of the Pacific white shrimp Penaeus (Litopenaeus) vannamei (Boone 1931)

The genetics of resistance to hypoxia was studied in shrimp using two approaches, heritability estimation and heterosis estimation. The heritability of resistance to hypoxia was evaluated in two populations of shrimp postlarvae families produced at different times, and heterosis was estimated through the reciprocal crosses of two genetically distinct shrimp populations at postlarvae and juvenile. Heritabilities of resistance to hypoxia in postlarvae were large and out of the range for the heritability (1.73 +/- 0.09, 1.35 +/- 0.14) regardless of population evaluated. When covariates (survival and mean total weight to postlarvae 15 days old) were introduced in the analyses to correct for effects during rearing of the larvae, the heritabilities did not change substantially for the first population, but were decreased for the second population depending on the covariate used for correction (1.15 +/- 0.10 and 1.08 +/- 0.11 for the covariates survival and total weight respectively). Those large heritabilities could be explained by the presence of confounded common environmental variance in the estimated genetic variance (maternal effects), or by dominance and epistatic effects being an important part of the estimated genetic variance. Heterosis analyses dissecting maternal effect indicated that both effects, maternal and dominance, are involved in the resistance to hypoxia at postlarvae, and that although maternal effects decreased at juvenile stage, the trait was still characterized by presenting a large heterosis value (62-65% for postlarvae and 36% for juveniles).