Hi Chris,
I think MCMCglmm is probably giving you the right answer. There are huge
chunks of the phylogeny that are either egg-laying and live-bearing. The
non-phylogenetic model shows a strong relationship between reproductive
mode and depth, and that might be causal or it might just be because
certain taxa tend to live at greater depths and *happen to have* the
same reproductive mode. There's not much information in the phylogenetic
spread of reproductive modes to distinguish between these hypotheses,
hence the wide confidence intervals. Just to be sure can you
a) just perform independent contrasts (not really suitable for binary
data, but probably won't give you an answer far off the truth and is a
nice simple sanity check).
b) using MCMCglmm (not MCMCglmmRAM) fit
prior.dep2<-=list(R=list(V=diag(1), fix=1), G=list(G1=list(V=diag(1),
nu=0.002)))
dep2<-MCMCglmm(parity~log.med.depth,
random=~animal,
rcov=~units,
pedigree=shark.tree,
data=traits,
prior=prior.dep2,
pr=TRUE,
pl=TRUE,
family="threshold")
an send me the summary and hist(dep2$Liab)
Cheers,
Jarrod
On 16/12/2016 07:02, Jarrod Hadfield wrote:
Hi Chris,
I think ngen in threshbayes is not the number of full iterations (i.e.
a full update of all parameters), but the number of full iterations
multiplied by the number of nodes (2n-1). With n=600 species this
means threshbayes has only really done about 8,000 iterations (i.e.
about 1000X less than MCMCglmm). Simulations suggest threshbayes is
about half as efficient per full iteration as MCMCglmm which means
that it may have only collected 0.5*1132/1200 = 0.47 effective samples
from the posterior. The very extreme value and the surprisingly tight
credible intervals (+/-0.007) also suggest a problem.
*However*, the low effective sample size for the covariance in the
MCMglmm model is also worrying given the length of chain, and may
point to potential problems. Are egg-laying/live-bearing scattered
throughout the tree, or do they tend to aggregate a lot? Can you send
me the output from:
prior.dep<-=list(R=list(V=diag(1)*1e-15, fix=1),
G=list(G1=list(V=diag(1), fix=1)))
dep<-MCMCglmm(parity~log.med.depth,
random=~animal,
rcov=~units,
pedigree=shark.tree,
reduced=TRUE,
data=traits,
prior=prior2,
pr=TRUE,
pl=TRUE,
family="threshold")
summary(dep)
summary(glm(parity~log.med.depth, data=traits,
family=binomial(link=probit)))
Cheers,
Jarrod
On 15/12/2016 20:59, Chris Mull wrote:
Hi All,
I am trying to look at the correlated evolution of traits using the
threshold model as implemented in phytools::threshBayes (Revell 2014) and
MCMCglmmRAM (Hadfield 2015). My understanding from Hadfield 2015 is that
the reduced animal models should yeild equivalent results, yet having run
both I am having trouble reconciling the results. I have a tree covering
~600 species of sharks. skates, and rays and am interested in testing for
the correlated evolution between reproductive mode (egg-laying and
live-bearing) with depth. When I test for this correlation using
phytools:threshBayes there is a clear result with a high correlation
coefficient (-0.986) as I would predict. When I run the same analysis using
MCMCglmmRAM I get a very different result, with a low degree of covariation
and CI crossing zero (-0.374; -3.638 - 3.163 95%CI). Both models are run
for 10,000,000 generations with the same bunr-in and sampling period. I
have looked at the trace plots for each model using coda and parameter
estimates and likelihodd . I'm not sure how to reconcile the differences in
these results and any advice would be greatly appreciated. I have appended
the code and outputs below.
#######################
#phytools::threshBayes#
#######################
X<-shark.data[c("parity","log.med.depth")]
X<-as.matrix(X)
#mcmc paramters (also see control options)
ngen<-10000000
burnin<-0.2*ngen
sample<-500
thresh<-threshBayes(shark.tree,
X,
types=c("discrete","continuous"),
ngen=ngen,
control = list(sample=sample))
The return correlation is -0.986 (-0.99 - -0.976 95%HPD)
#############################
#MCMCglmm bivariate-gaussian#
#############################
prior2=list(R=list(V=diag(2)*1e-15, fix=1), G=list(G1=list(V=diag(2),
nu=0.002, fix=2)))
ellb.log.dep<-MCMCglmm(cbind(log.med.depth,parity)~trait-1,
random=~us(trait):animal,
rcov=~us(trait):units,
pedigree=shark.tree,
reduced=TRUE,
data=traits,
prior=prior2,
pr=TRUE,
pl=TRUE,
family=c("gaussian", "threshold"),
thin=500,
burnin = 1000000,
nitt = 10000000)
summary(ellb.log.dep)
Iterations = 1000001:9999501
Thinning interval = 500
Sample size = 18000
DIC: 2930.751
G-structure: ~us(trait):animal
post.mean l-95% CI u-95% CI eff.samp
traitscale.depth:traitscale.depth.animal 16.965 15.092 18.864
18000
traitparity:traitscale.depth.animal -0.374 -3.638 3.163
1132
traitscale.depth:traitparity.animal -0.374 -3.638 3.163
1132
traitparity:traitparity.animal 1.000 1.000 1.000
0
R-structure: ~us(trait):units
post.mean l-95% CI u-95% CI eff.samp
traitscale.depth:traitscale.depth.units 16.965 15.092 18.864 18000
traitparity:traitscale.depth.units -0.374 -3.638 3.163 1132
traitscale.depth:traitparity.units -0.374 -3.638 3.163 1132
traitparity:traitparity.units 1.000 1.000 1.000 0
Location effects: cbind(scale.depth, parity) ~ trait - 1
post.mean l-95% CI u-95% CI eff.samp pMCMC
traitscale.depth 0.12297 -3.63655 4.02005 18000 0.949
traitparity -0.02212 -1.00727 0.93387 17058 0.971
Thanks for any and all input.
Cheers,
Chris
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