Models with indirect genetic effects depeding on group sizes - A simulation study assessing the precision of the estimates of the dilution

With social interactions, the phenotype of an individual is influenced by the direct genetic effect (DGEs) of the individual, as well as the indirect genetic effects (IGEs) of its group mates. With IGEs, the heritable variance and response to selection depend on the group size. The change of IGE with group size can be modelled via a 'dilution' parameter ( d ), which reflects the magnitude of IGE as a function of group size. Very little is known of the estimability of d and the precision of its estimate. The relevance of d estimation is due to its impact on the dynamics of response to selection and heritable variation. We simulated data with varying group sizes and estimated d using IGE models including d parameter. Schemes investigated differed with respect to average group size (4, 6 or 8) and variability of group size (coefficient of variation= CV , ranging from 0.125 to 1.010) obtained based on either 2 or 3 group sizes within a scheme. A design where individuals were randomly allocated to groups was used to estimate d . Results showed that it was possible to estimate d in data with varying group sizes. All estimates were unbiased. With larger CV of group sizes, d could be estimated more precisely. Estimation of the relationship between the magnitude of IGEs and group size would allow for proper interpretation of direct and indirect variance components that contributes to heritable variation in relation to group size.