Genotype by environment interaction for shell length in Mytilus galloprovincialis

Abstract

Several drawbacks have emerged on the welfare status of shellfishes grown intensively in natural estuaries, such as density-dependent competition, overexploitation, low growth, and harmful algae blooming episodes (HAB), which anticipate profound socioeconomic consequences. The improvement of body size would hitchhike other growth surrogates and is a natural solution to increase productivity and circumvent HAB by shortening the production cycle. Such improvement in aquaculture depends on the existence of genotypic variation in quantitative traits. Namely, heritability plays a predictive role in the study of metric characters because it measures the resemblance between the phenotypic value and the breeding value. The aim of this study was to estimate variance components and interaction phenomena on shell length of the quasi-sessile marine invertebrate M. galloprovincialis grown in a Hatchery Environment Nucleus (HEN) and replicated in a Production Environment (PDE). A large amount of additive variation for shell length exists in M. galloprovincialis which broad-sense heritability after the animal model was higher in the richer production environment (h¯2AM_PDE = 0.643 ± 0.066) than in the hatchery environment (h¯2AM_HEN = 0.606 ± 0.127). The stability of the phenotypic variation (Vp) observed in HEN, suggests the increasing weight of the non-additive genetic variance which makes h2 increase with age. The reaction norm showed a reduced phenotypic variance in PDE as a byproduct of a change in scale as well as in ranking due to the presence of Genetic by Environment Interaction (GEI). Therefore, quantitative parameters recorded in the farm (HEN) should not be employed to extrapolate potential growth in the production field (PDE). Provided that selection accuracy depends on both, Family by Environment Interaction (FEI) and GEI, evaluation in the breeding nucleus entailed a global 5.35% gain overestimation (∆G= + 3.74 mm in shell length) on the expected phenotypic gain in PDE of the directional L lines constructed. Correction for accuracy and genetic correlation indicates that a selective breeding program for directional selection could yield a 9% (6 mm in shell length) gain in the first generation at PDE what could allow to attain a significant production cycle shortening in few generations of selection.