Abstract

Selection, either natural or artificial, induces an inter-generational response only when the trait exhibits additive genetic variation. An index of additive genetic variation is narrow-sense heritability (h 2): the ratio between additive genetic variance and phenotypic variance. Here, we present narrow-sense heritabilities for mass and size in the Chilean blue mussel Mytilus chilensis at different ages and in three different populations. We found that h 2 changed with age and that maternal-non-additive variance was high, generating relatively low estimates of h 2 in most cases. Our results, together with previous studies, suggest that genotype-by-environment interaction does not appear to play a significant role. However, we found that non-additive and common environmental variance are important determinants of phenotypic morphological variation in body size in M. chilensis. Further studies are needed to establish the precise contributions of these sources of variation, to assess the real potential for response to selection. © 2007 Blackwell Publishing Ltd.