A genetic analysis of intraspecific competition for growth in mussel cultures

In domestic organisms that are cultured in situations where competition for resources exists, the effect of an individual on the overall yield of the population depends not only on its own growth in the face of competition, but also on its competitive influence on its neighbours' growth. The genetic variability of this influence may be very important and therefore useful in a breeding plan, but is seldom estimated in practice. In this study, we carried out a genetic analysis of the intraspecific competition for growth in cultured mussels, and found that the family genotype had a clear effect on both the competitive influence of each individual on its neighbours, and its response to the competition from them. The limited number of male and female parents available for the experiment prevented a very precise partition of this genetic variability in additive and dominant variances, but in any case the heritability estimates obtained tended to be low (about 10% overall). These low heritabilities could still result in significant responses to artificial selection, given the high selection pressures that can be applied in bivalve molluscs, In addition, and in contrast with what usually happens in plants, the correlation between both kinds of effects in our mussel population was clearly greater than - 1, which could allow the use of artificial selection to increase the ability to grow at high population densities and simultaneously to reduce the competitive interference between neighbours. (C) 2001 Elsevier Science B.V. All rights reserved.