The other day I was emailed the following question:

*“I would like to know if the function recently implemented in phytools
( cophylo) allows for colorizing internal clades in the tree.
The reason I wanted to do this is to show a more detailed view of the
relationships between the two trees that are being compared with the
function…. If this feature is not available in phytools, would you be able
to add it?”*

Indeed, this feature is not available in the current version of phytools.
`plot.cophylo`

uses a different function for plotting trees -
the internal phytools function, `phylogram`

, rather than the
function `plotSimmap`

that is used by many of phytools' other
plotting methods.

However, it is indeed possible to add. I have just pushed this update to GitHub.

The most complicated thing is that in the existing tree plotter vertical lines
are plotted as a single line segment; however, for the case of coloring
different edges, we can anticipate a case in which the vertical lines of our
right- or left-facing phylograms have descendant edges with different colors.
For this circumstance, we want to be able to split the line into two
differently colored segments. I accomplished this by substituting the function
`segments`

for `lines`

in plotting the vertical lines of
the tree.

Even more complicated is the situation in which multiple edges descend from a single node - potentially with different colors. In this case, I decided to pick the midpoint of the vertical line & plot line segments to the north or south of this midpoint the same color as their respective descendant edges.

First, let's try it using random color assignments:

```
library(phytools)
packageVersion("phytools")
```

```
## [1] '0.6.6'
```

```
t1
```

```
##
## Phylogenetic tree with 26 tips and 19 internal nodes.
##
## Tip labels:
## A, S, I, X, Q, K, ...
##
## Unrooted; includes branch lengths.
```

```
t2
```

```
##
## Phylogenetic tree with 26 tips and 19 internal nodes.
##
## Tip labels:
## Q, P, Y, O, H, T, ...
##
## Rooted; includes branch lengths.
```

```
obj<-cophylo(t1,t2)
```

```
## Rotating nodes to optimize matching...
## Done.
```

```
plot(obj,link.type="curved")
```

```
edge.col<-list(
left=sample(c("red","blue"),nrow(t1$edge),replace=TRUE),
right=sample(c("red","blue"),nrow(t2$edge),replace=TRUE))
edge.col
```

```
## $left
## [1] "red" "blue" "blue" "red" "red" "blue" "blue" "blue" "blue" "blue"
## [11] "red" "red" "blue" "blue" "red" "blue" "red" "red" "red" "red"
## [21] "red" "red" "red" "blue" "blue" "red" "red" "red" "blue" "red"
## [31] "red" "blue" "blue" "red" "red" "red" "red" "blue" "red" "blue"
## [41] "red" "blue" "blue" "blue"
##
## $right
## [1] "red" "red" "blue" "blue" "red" "red" "red" "blue" "red" "blue"
## [11] "red" "blue" "blue" "blue" "red" "red" "red" "red" "blue" "blue"
## [21] "red" "blue" "blue" "blue" "red" "red" "blue" "blue" "blue" "red"
## [31] "blue" "red" "red" "red" "red" "blue" "red" "blue" "blue" "blue"
## [41] "red" "blue" "red" "blue"
```

```
plot(obj,link.type="curved",edge.col=edge.col)
```

We can also color clades or parts of the tree as desired. This requires
identifying the set of edges *in the rotated trees* that correspond
with the clades we would like to color. For instance:

```
plot(obj,link.type="curved")
nodelabels.cophylo(which="left")
nodelabels.cophylo(which="right")
```

```
left<-rep("black",nrow(obj$trees[[1]]$edge))
nodes<-getDescendants(obj$trees[[1]],36)
left[sapply(nodes,function(x,y) which(y==x),y=obj$trees[[1]]$edge[,2])]<-
"red"
nodes<-getDescendants(obj$trees[[1]],43)
left[sapply(nodes,function(x,y) which(y==x),y=obj$trees[[1]]$edge[,2])]<-
"blue"
right<-rep("black",nrow(obj$trees[[2]]$edge))
nodes<-getDescendants(obj$trees[[2]],30)
right[sapply(nodes,function(x,y) which(y==x),y=obj$trees[[2]]$edge[,2])]<-
"red"
nodes<-getDescendants(obj$trees[[2]],42)
right[sapply(nodes,function(x,y) which(y==x),y=obj$trees[[2]]$edge[,2])]<-
"blue"
edge.col<-list(left=left,right=right)
edge.col
```

```
## $left
## [1] "black" "black" "black" "black" "black" "black" "black" "black"
## [9] "black" "black" "black" "black" "black" "black" "black" "black"
## [17] "black" "black" "black" "red" "red" "red" "red" "red"
## [25] "red" "red" "red" "red" "red" "red" "red" "red"
## [33] "black" "black" "black" "black" "blue" "blue" "blue" "blue"
## [41] "blue" "blue" "blue" "black"
##
## $right
## [1] "black" "black" "black" "black" "black" "red" "red" "red"
## [9] "red" "red" "red" "red" "red" "red" "red" "red"
## [17] "red" "red" "red" "red" "red" "red" "red" "red"
## [25] "red" "red" "red" "red" "black" "black" "black" "black"
## [33] "black" "black" "black" "blue" "blue" "blue" "blue" "blue"
## [41] "blue" "blue" "blue" "blue"
```

```
plot(obj,link.type="curved",edge.col=edge.col,lwd=2)
```

Hopefully, you get the idea.

The trees for this exercise were simulated as follows:

```
t1<-rtree(n=26,tip.label=LETTERS)
t2<-rtree(n=26,tip.label=LETTERS)
internal<-which(t1$edge[,2]>Ntip(t1))
t1$edge.length[sample(internal,6)]<-0
t1<-di2multi(t1)
internal<-which(t2$edge[,2]>Ntip(t2))
t2$edge.length[sample(internal,6)]<-0
t2<-di2multi(t2)
```

Hi Liam !

ReplyDeleteGreat Job here!

Is there any way to specify a cex parameter for the tiplabels ?

Thanks a lot !

Pierre

Sorry Liam, just found the answer with the 'fsize' parameter.

DeleteAn other question : Is there any way to cophylo two trees of which one (A) has fewer species than the other (B) (but the B tree has all A species).

Pierre