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effective sample size in MCMCglmm

Rechecking your model, I noticed you have set the burnin at 250000 and your
thin at 10000 which resulted in a very small sample size for your
estimates, meaning your posterior distribution is based on a very small
sample of saved iterations of the chain. The setting suggested is
burnin=2500000, thin=500000 (which means we end up with 2 million
iterations of the chain) and thin=2000 (this way we end up with a 1000
sample size which is acceptable, i.e. 2000000/2000).

Another suggestion would be to use expanded parameters for your priors to
better the convergence of the model. I can't specifically suggest to you
what prior to specify but reading the "Parameter-expanded priors" section
in the coursenotes of the MCMcglmm package by Hadfield (2010) would be a
good place to start.

Good luck