---
title: "Detecting rogue taxa in Bayesian posterior tree sets"
author: "[](https://orcid.org/0000-0001-5660-1727)Martin R. Smith, Durham University"
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
bibliography: ../inst/REFERENCES.bib
csl: ../inst/apa-old-doi-prefix.csl
vignette: >
%\VignetteIndexEntry{Detecting rogue taxa in Bayesian posterior tree sets}
%\VignetteDepends{PlotTools}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteEncoding{UTF-8}
---
Detecting "rogue" taxa and removing them from summary trees can produce
consensus trees with a higher resolution, and can reveal strong support
for groupings that would otherwise be masked by the uncertain position of
rogues.
The raw output of Bayesian analysis requires a little processing
before rogue taxa can be identified and explored using the "Rogue" R package.
The workflow presented here should be reasonably easy to adapt for the output
of any Bayesian phylogenetic analysis, but if you hit snags or get stuck please
let me know by
[filing a GitHub issue](https://github.com/ms609/Rogue/issues/new?title=Bayesian+vignette)
or by e-mail.
## Set up
Let's start by loading the packages we'll need:
```{r load-packages, message = FALSE}
library("TreeTools") # Read and plot trees
library("Rogue") # Find rogue taxa
```
```{r test-connection, echo = FALSE}
online <- tryCatch({
read.csv("https://raw.githubusercontent.com/ms609/hyoliths/master/MrBayes/hyo.nex.pstat")
TRUE
},
warning = function(w) invokeRestart(""),
error = function(e) FALSE
)
```
We'll work with some example data generated from a morphological
analysis of early brachiopods [@Sun2018] using
[MrBayes](https://nbisweden.github.io/MrBayes/) [@Hulsenbeck2001].
Our data files are stored on
[GitHub](https://github.com/ms609/hyoliths/tree/master/MrBayes).
Let's load the results of run 1:
```{R load-trees}
if (online) {
dataFolder <- "https://raw.githubusercontent.com/ms609/hyoliths/master/MrBayes/"
run1.t <- paste0(dataFolder, "hyo.nex.run1.t")
# Reading 10k trees takes a second or two...
run1Trees <- ape::read.nexus(run1.t)
if (packageVersion('ape') <= "5.6.1") {
# Workaround for a bug in ape, hopefully fixed in v5.6.2
run1Trees <- structure(lapply(run1Trees, function(tr) {
tr$tip.label <- attr(run1Trees, 'TipLabel')
tr
}), class = 'multiPhylo')
}
} else {
# If no internet connection, we can generate some example trees instead
run1Trees <- structure(unlist(lapply(0:21, function(backbone) {
AddTipEverywhere(ape::as.phylo(0, nTip = 12), 'ROGUE')
}), recursive = FALSE), class = 'multiPhylo')
}
```
## Select trees to analyse
Our tree file contains all trees generated. We typically want to discard
a proportion of trees as burn-in:
```{R discard-burnin}
burninFrac <- 0.25
nTrees <- length(run1Trees)
trees <- run1Trees[seq(from = burninFrac * nTrees, to = nTrees)]
```
This is a large number of trees to analyse. We could save time for an initial
analysis by thinning our sample somewhat.
```{R thin-trees}
sampleSize <- 100
trees <- run1Trees[seq(from = burninFrac * nTrees, to = nTrees,
length.out = sampleSize)]
```
For a full analysis, we ought to consider the output from the other runs of our
analysis, perhaps with
```r
nRuns <- 4
allTrees <- lapply(seq_len(nRuns), function(run) {
runTrees <- ape::read.nexus(paste0(dataFolder, 'hyo.nex.run', run, .'t'))
runTrees <- runTrees[seq(from = burninFrac * nTrees, to = nTrees,
length.out = sampleSize / nRuns)]
})
trees <- structure(unlist(allTrees, recursive = FALSE), class = 'multiPhylo')
```
## Initial appraisal
Let's start by looking at the majority rule consensus tree.
It can be instructive to colour leaves by their instability; here we use
the _ad hoc_ approach of @SmithCons.
First let's define a function to plot a gradient legend:
```{r initial-view, fig.width = 8, fig.asp = 2/3}
plenary <- Consensus(trees, p = 0.5)
par(mar = rep(0, 4), cex = 0.85)
plot(plenary, tip.color = ColByStability(trees))
PlotTools::SpectrumLegend(
"bottomright", legend = c("Stable", "Unstable"),
palette = hcl.colors(131, 'inferno')[1:101]
)
```
Some taxa stand out as having a less stable position on the tree than others.
Will removing those taxa reveal enough additional information about the
remaining taxa to compensate for the loss of information about where those
taxa plot?
## Detect rogue taxa
We have a few options for how we evaluate the negative impact of retaining
these rogue taxa in our consensus tree.
`QuickRogue()` uses the quick heuristic method of @SmithCons;
`RogueTaxa()` supports Smith's slower heuristic, which might find a set of
rogue taxa that yield slightly more improvement to a consensus tree;
it can also be configured to employ the RogueNaRok approach [@Aberer2013].
```{R find-rogues}
rogues <- QuickRogue(trees)
# rogues <- RogueTaxa(trees) might do a better job, much more slowly
rogues
# The first line reports the information content of the plenary tree
rogueTaxa <- rogues$taxon[-1]
```
## Visualize results
Let's see how these taxa influence the majority rule consensus of our results.
Removing rogues may reveal information by producing reduced consensus trees
with a higher resolution, or with higher split support values.
```{R trees, fig.asp = 1.2/2, fig.width = 8}
par(mar = rep(0, 4)) # Remove plot margin
par(mfrow = c(1, 2)) # Multi-panel plot
par(cex = 0.85) # Smaller labels
plenary <- Consensus(trees, p = 0.5)
reduced <- ConsensusWithout(trees, rogueTaxa, p = 0.5)
plot(plenary,
tip.color = ifelse(plenary$tip.label %in% rogueTaxa, 2, 1))
LabelSplits(plenary, SplitFrequency(plenary, trees))
plot(reduced)
LabelSplits(reduced, SplitFrequency(reduced, trees))
```
We can also visualize the locations where our rogue taxa would plot on the
reduced consensus tree: the rogue occurs more frequently at the brighter
locations.
```{r rogue-plot-trees, fig.width = 8, fig.asp = 2/3}
par(mar = rep(0, 4), cex = 0.8)
whichTaxon <- length(rogueTaxa) # Select an illuminating taxon
positions <- RoguePlot(trees, rogueTaxa[whichTaxon], p = 0.5,
legend = "bottomleft", legend.inset = 0.06)
```
## References