In PuttickMacroevolution/MCMCtreeR: Prepare MCMCtree Analyses and Plot Bayesian Divergence Time Analyses Estimates on Trees

library(knitr)
opts_chunk$set(tidy.opts=list(width.cutoff=60),tidy=TRUE)

knitr::opts_chunk$set(fig.pos = 'H')

This is a guide for the R program MCMCtreeR.

MCMCtreeR contains functions to set up analyses in the MCMCtree program. The functions here help users choose the best parameters to reflect age information for prior age distributions, visualise time priors, and produce output files ready to be used in MCMCtree. A seperate vignette is available to explain the plotting options for timescaled trees in MCMCtreeR.

MCMCtree is a Bayesian program in the software PAML that estimates divergence times on fixed topologies using molecular data, developed by Ziheng Yang. The program requires various inputs from the user: a phylogeny, molecular sequence alignment, and selected model parameters. This guide does not include details about which time and other priors are most appropriate for the data, etc., so please see the MCMCtree manual for more information.

Installation

if(!any(rownames(installed.packages()) == "MCMCtreeR")) install.packages("MCMCtreeR")
library(MCMCtreeR, quietly=TRUE, warn.conflicts=FALSE)

The examples here use a phylogeny of apes and associated age information. These data are a phylogeny of apes apeTree, the minimum ages for internal nodes minimumTimes, maximum ages for internal nodes maximumTimes, and the tip labels descending from each node monophyleticGroups. These example data can be substituted for other data.

data(apeData)
attach(apeData)
names(apeData)
minimumTimes
maximumTimes
monophyleticGroups
apeTree

The order of the data must match in the minimumTimes, maximumTimes, and monophyleticGroups objects. These data do not need to be given in the order they appear in the tree, but the order must match in each object. For example, if the minimum age for the root is the first element in minimumTimes it must also be the first element in the minimumTimes and monophyleticGroup objects.

For this example there are four calibrated nodes. The MCMCtree function tipDes can be used to recreate the monophyleticGroups list object. First the ape package is used to plot the tree and view the node label numbers.

plot(apeTree)
nodelabels()
tipDes(apeTree, 10)

The calibrated nodes in this example are 8, 10, 11, and 13. The function tipDes takes the tree and node numbers as input and returns the taxon names that descend from that node; this output can be used directly in the functions below.

monophyleticGroups.user <- tipDes(apeTree, c(8, 10, 11, 13))
monophyleticGroups.user

Estimate parameters for node input parameters

This section includes information to estimate and plot prior age distributions for node(s) used in MCMCtree divergence time estimation. The data required to do this are a phylogeny, minimum and maximum ages for the nodes with prior distributions, and taxa that descend from each node (please see above for information on how to make this various objects).

The code can be used to simultaneously estimate the parameter values that reflect the a priori time information for nodes and write files ready for MCMCtree input. MCMCtreeR can produce output files with the same type of distributions used to summarise a priori time information for all nodes, or different distributions can be used to reflect uncertainty on different internal nodes.

The functions here estimates the distribution parameters so that the distribution spans for user-supplied minimum bounds (lower age) and maximum bounds (upper age). By default, minimum ages are treated as 'hard' constraints and maximum ages are 'soft'. The function then ensures that 97.5% of the distribution falls between these minimum and maximum ages. The code can estimate paramaters for the Cauchy, Skew t, Skew-normal, and Gamma distirbutions shown in the MCMCtree manual on page 49, and calibrated node priors can also be placed on trees for uniform (bound), fixed, and upper age.

For each function, if only a single value is provided for each parameter by the user, the function outputs warnings to indicate these values are recycled for each node.

Skew t

estimate scale with a given shape

The default arguments in the estimateSkewT assumes the user wants to estimate the scale of the distribution with a given shape value (the default shape value is 50). The function estimates the parameters with the user-supplied minimum and maximum ages for all nodes, and the monophyletic groups that define the nodes.The output skewT_results$MCMCtree shows the estimated parameters in the input ready for MCMCtree. Here the parameters for the Skew t distributions are the location (lower node age), scale, shape, and degrees of freedom.

skewT_results <- estimateSkewT(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, phy=apeTree, plot=FALSE)
skewT_results$MCMCtree

As explained above, if only a single value is provided for each parameter by the user, the function outputs warnings to indicate these values are recycled for each node.

The function plotMCMCtree plots the estimated age distributions given these parameters.

par(mfrow=c(2,2), family="Palatino")
for(i in 1:4) plotMCMCtree(skewT_results$parameters[i,], method="skewT", title=paste0("node ", i), upperTime=max(maximumTimes))
skewT_results$MCMCtree

If the distributions are acceptable, the output can be written into a tree file ready to be input into MCMCtree using the function estimateSkewT. The functions will be written when the argument writeMCMCtree is set to TRUE, and the file is set using the MCMCtreeName argument. Additionally, a PDF file is output showing the estimated distributions if plot=TRUE and the file name can be specifying using the argument pdfOutput.

# result in tree MCMCtree format
skewT_results$MCMCtree
## not run
## skewT_results <- estimateSkewT(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, phy=apeTree, plot=FALSE, pdfOutput="skewTPlot.pdf", writeMCMCtree=TRUE, MCMCtreeName="skewTInput.tre")

It is not necessary to specify the same shape value for each parameter: a different value of the shape parameter can be set for each distribution.

## not run (remove ## to run)
## skewT_results <- estimateSkewT(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, shape=c(9, 10, 8, 10), phy=apeTree, plot=TRUE, pdfOutput="skewTPlot.pdf", writeMCMCtree=TRUE, MCMCtreeName="skewTInput.tre")
## skewT_results$parameters

estimate shape with a given scale

The function estimateSkewT will take input minimum input times, and estimate the value of the shape that will produce the desired distribution with the scale parameter set to 0.05.

skewT_results <- estimateSkewT(minAge=minimumTimes[2], maxAge=maximumTimes[2], monoGroups=monophyleticGroups, scale=0.05, estimateShape=TRUE, estimateScale=FALSE, phy=apeTree, plot=FALSE, writeMCMCtree=FALSE)
skewT_results$parameters

Skew normal

The estimateSkewNormal function estimates the value of the scale that will produce a skew normal distribution with the 97.5% cumulative probability of the distribution at the maximum age.

skewNormal_results <- estimateSkewNormal(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, addMode=0.05, phy=apeTree, plot=FALSE)
skewNormal_results$parameters

These skew normal distributions can also be plotted to the screen.

par(mfrow=c(2,2), family="Palatino")
for(i in 1:4) plotMCMCtree(skewNormal_results$parameters[i,], method="skewNormal", title=paste0("node ", i), upperTime=max(maximumTimes))

Cauchy

Here the estimateCauchy function is used to estimate parameters and plot the example on page 49 of PAML manual.

example_page_50 <- estimateCauchy(minAge=1, maxAge=4.32, monoGroups=monophyleticGroups[[1]],   phy=apeTree,  offset=0.5, minProb=0.025, plot=FALSE)[[1]]
plotMCMCtree(example_page_50, method="cauchy", title=paste0("node ", i), upperTime=max(maximumTimes))

estimate scale with a given shape

The estimateCauchy function will take minimum input times, and estimate the value of the scale parameter that will produce a Cauchy distribution with the 97.5% cumulative probability of the distribution at the user-supplied maximum age.

cauchy_results <- estimateCauchy(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups,  offset=0.5, phy=apeTree, plot=FALSE)
cauchy_results$parameters
par(mfrow=c(2,2), family="Times")
for(i in 1:4) plotMCMCtree(cauchy_results$parameters[i,], method="cauchy", title=paste0("node ", i), upperTime=max(maximumTimes))

These plots indicate we may have constrained our distribution too much for the 2nd, 3rd, and 4th distribution so we can modify that to allow for a smaller offset.

cauchy_results <- estimateCauchy(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups,  offset=c(0.5, 0.1, 0.1, 0.05), phy=apeTree, plot=FALSE)
cauchy_results$parameters
par(mfrow=c(2,2), family="Times")
for(i in 1:4) plotMCMCtree(cauchy_results$parameters[i,], method="cauchy", title=paste0("node ", i), upperTime=maximumTimes[i])

Uniform distribution

uniform_results <- estimateBound(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, phy=apeTree, plot=FALSE)
uniform_results$parameters
par(mfrow=c(2,2), family="Palatino")
for(i in 1:4) plotMCMCtree(uniform_results$parameters[i,], method="bound", title=paste0("node ", i), upperTime=maximumTimes[i]+1)

Gamma distribution

gamma_results <- estimateGamma(minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, alpha=188, beta=2690, offset=0.1, phy=apeTree, plot=FALSE)
gamma_results$parameters
par(mfrow=c(2,2), family="Palatino")
for(i in 1:4) plotMCMCtree(gamma_results$parameters[i,], method="gamma", title=paste0("node ", i), upperTime=maximumTimes[i])

Upper Age

upper_results <- estimateUpper(maxAge=maximumTimes, monoGroups=monophyleticGroups, rightTail=0.025, phy=apeTree)
upper_results$parameters

Fixed ages

fixed_results <- estimateFixed(minAge=minimumTimes[1], monoGroups=monophyleticGroups[[1]], phy=apeTree)
fixed_results 

Different parameters on different nodes

It is possible to specify different node calibration distributions to each calibrated node. we can specify this by using the MCMCtreePhy function. Here there are different distributions applied to the internal nodes: a fixed root (node 1), skew normal (node 2), gamma (node 3), and upper distribution (node 4). For each input we give the associated parameter values in a vector in the order of nodes. i.e., for the minProb on four nodes can be set as 1, 2, 4 to be 1e-8 and node 3 to be 0.025

each.node.method <- c("skewT", "cauchy", "gamma", "upper")
output.full <- MCMCtreePhy(phy=apeTree, minAge=minimumTimes, maxAge=maximumTimes, monoGroups=monophyleticGroups, method=each.node.method, writeMCMCtree = FALSE)

This can fine-tuned. For example, to estimate alpha not beta for the 3rd node

estimate.alpha <- c(FALSE, FALSE, TRUE, FALSE)
estimate.beta <- c(TRUE, TRUE, FALSE, TRUE)
outputFull <- MCMCtreePhy(phy=apeTree, minAges=minimumTimes, maxAges=maximumTimes, monoGroups=monophyleticGroups, method=each.node.method, estimateAlpha=estimate.alpha, estimateBeta=estimate.beta, alpha=188, beta=100, writeMCMCtree = FALSE)

Outputs from individual methods can be added to the input for subsequent node estimation. This allows for easier fine-tuning. Perhaps easier to explain with an example. Here, a skew normal calibration is applied to the first node.

skewNormal_results_nodeOne <- estimateSkewNormal(minAge=minimumTimes[1], maxAge=maximumTimes[1], monoGroups=monophyleticGroups[[1]], addMode=0.05, phy=apeTree, plot=FALSE, writeMCMCtree = FALSE)
skewNormal_results_nodeOne$apePhy

This output is then used as input in estimateCauchy to estimate parameters for a Cauchy distribution, which is applied to the second node.

cauchy_results_nodeTwo <- estimateCauchy(minAge=minimumTimes[2], maxAge=maximumTimes[2], monoGroups=monophyleticGroups[[2]],  offset=0.5, phy=skewNormal_results_nodeOne$apePhy, plot=FALSE, writeMCMCtree = FALSE)
cauchy_results_nodeTwo$apePhy

The third node is the set as a uniform distribution.

uniform_results_nodeThree <- estimateBound(minAge=minimumTimes[3], maxAge=maximumTimes[3], monoGroups=monophyleticGroups[[3]], phy=cauchy_results_nodeTwo$apePhy, plot=FALSE, writeMCMCtree = FALSE)
uniform_results_nodeThree$apePhy

The fourth is a skewT distribution, and the tree can be written to file for input into MCMCtree.

## not run
# skewT_results_nodeFour <- estimateSkewT(minAge=minimumTimes[4], maxAge=maximumTimes[4], monoGroups=monophyleticGroups[[4]], scale=0.5, phy=cauchy_results_nodeTwo$apePhy, plot=FALSE, writeMCMCtree = TRUE)
# skewT_results_nodeFour$apePhy

PuttickMacroevolution/MCMCtreeR documentation built on Nov. 24, 2019, 5:22 a.m.