Estimating variance components and heritabilities in the wild: a case study using the 'animal model' approach

Using a genealogy containing over 1800 dams and nearly 400 sires (estimated by genetic paternity techniques), combined with maximum likelihood procedu res and an 'animal model', we have estimated the heritabilities, genetic co rrelations and variance components of three morphometric traits in the Soay sheep (Ovis aries) on St Kilda, Scotland. This approach allows heritabilit ies to be estimated in natural populations that violate the assumptions of offspring-parent regression methods. Maternal (or paternal) effects can als o be estimated under natural conditions. We demonstrate that all the traits , body weight, hind leg length and incisor arcade breadth, have low but sig nificant heritabilities. Body weight, the trait that experiences the strong est selection, had the lowest heritability but the highest additive genetic coefficient of variation. An evolutionary response to selection is predict ed. When maternal effects were not taken into consideration heritabilities were over-estimated, although this effect was only significant in female of fspring.