[R] Mixed-effects models / heterogeneous covariances

[Lutz Ph. Breitling]

Dear R-list,

maybe someone can help me with the following mixed-effects models
problem, as I am unable to figure it out with the 'nlme-bible'.

I would like to fit (in R, obviously) a so-called animal model (google
e. g. "Heritability and genetic constraints of life-history" by Pettay
et al.) to estimate the variance component that is due to genetic
effects. The covariances of the genetic random effects between
observations are given by the different degrees of relatedness between
the individuals examined. (I find it difficult to explain, but Pettay
et al. describe it nicely in their methods section...)

Is there any straight-forward way to fit such a model with R? I first
thought I could handle it somehow with nlme's correlation structures,
but these within-group structures are quite a different thing, right?

Any suggestions would be highly appreciated-
Lutz

--
Lutz Ph. Breitling
University of Leeds/UK