[R] Help with Subtracting an effect from a Mixed Model

[Matthew Forister]

Hi Everyone,

I posted a similar question about a week ago, but haven't gotten any 
replies -- I'm afraid that's because my previous question was too 
vague.  Let me try again with a more specific question, and I hope 
someone can help.  NOTE, I know I should be using the newer lme4 
package, I just haven't had a chance to update my version of R yet, so 
the question below relates to nmle.

I have data from a classical quantitative genetics experiment, with 33 
sires mated each to 2 dams, with 15 progeny from each dam raised on 5 
host plants (3 larvae per host).  So the model I would like to run has 
the following factors:
Host (fixed)
Sire (random)
Dam [nested within sire] (random)
Host * Sire (random interaction)
Host * Dam [nested within sire] (random interaction)

This is the code I am using for that complete model:
lme1=lme(gain~host,random=~host|sire/dam)
I would like to try the model with and without each of those random 
interactions (host*sire and host*dam-nested-within-sire).

WHAT IS THE SYNTAX FOR SUBTRACTING AN EFFECT FROM THE RANDOM STATEMENT?
I have tried:
lme1=lme(gain~host,random=~host|sire/dam-sire:host)
But I get an "Invalid formula for groups" error.
Alternatively, I tried reorganizing the code, so that the interaction 
would be left out.  But there is no way to take out host*sire while 
still leaving in host*dam nested within sire.

any help will be greatly appreciated!
Matt

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Matthew L Forister
Department of Ecology and Evolution
State University of New York at Stony Brook
650 Life Sciences Building
Stony Brook, New York 11794-5245
Email: forister at life.bio.sunysb.edu
Webpage: http://life.bio.sunysb.edu/~forister/
Lab phone: (631) 632-8609
Fax: (631) 632-7626
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