Tanglegram is a representation of co-phylogeny where two phylogenetic trees are linked. This method is super useful to visualize common traits shared by both trees. For example, it can be used to visualize host-pathogen (or host-symbiotic) evolution and visualize if there is any phylogenetic concordance between the two phylogenetic trees.
I was in need to visualize co-phylogeny of phylogenetic tree reconstructed from chromosomal and symbiotic genes. Surprisingly, I didn’t find any strait-forward solution in R that can be used for drawing tanglegram. Particularly I wanted to leverage the beautiful `ggtree` library. After trying out several methods, I found the following approach works well for me so far.
In this post, I’m going to use two toy trees with the following Newick format. Note that they have the same isolate, but different tree-topology (since supposedly different gene-set were used to reconstruct them).
Tree 1: (((((((A:4,B:4):6,C:5):8,D:6):3,E:21):10,((F:4,G:12):14,H:8):13):13,((I:5,J:2):30,(K:11,L:11):2):17):4,M:56); Tree 2: (((((((F:8,I:18,G:4):2,C:5):3,M:6):3,E:21):10,((A:2,B:2):4):3):13,((K:5,L:2):20,(H:18,J:11):2):17):4,D:56);
We might be interested to visualize one (or more) interesting feature(s) (i.e. genotype) associated with the isolates in both trees. Our meta-file looks like the following:
Let’s load the necessary packages.
library(ggplot2) library(ggtree) library(phangorn) library(dplyr)
The best thing about `ggtree` is you can attach any feature(s) associated with isolates using a simple CSV file. Just make sure that the first column of your metafile has the same isolate names as used in the tree. Let’s load the metafile and both phylogenetic tree to be used. I also like to do midpoint rooting at this point.
# Meta file meta <- read.table('~/path/to/meta.csv', sep=',', header = T) # Load tree 1 tree1 <- read.tree('~/path/to/tree1.nwk') tree1 <- midpoint(tree1) # Load tree 2 tree2 <- read.tree('~/path/to/tree2.nwk') tree2 <- midpoint(tree2)
Let’s combine the meta feature dataset with both phylogenetic trees and visualize how they look.
t1 <-ggtree(tree1) %<+% meta + geom_tiplab() t2 <- ggtree(tree2) %<+% meta + geom_tiplab() t1 t2
Now we are going to draw both trees in a single figure. We also want to flip tree 2, for which we need to change the x-coordinates in that tree.
d1 <- t1$data d2 <- t2$data d1$tree <-'t1' d2$tree <-'t2' d2$x <- max(d2$x) - d2$x + max(d1$x) + max(d1$x)*0.3 pp <- t1 + geom_tree(data=d2) pp
In the above code block, we are grabbing the backend data frame from both trees and updating the tree 2 data frame x-coordinate. We are using this equation for the update: ‘max(d2$x) – d2$x + max(d1$x) + max(d1$x)*0.3’. You can toy with different values depending on the branch length unit of your tree to get good visualization (I particularly suggest changing max(d1$x)*0.3 terms).
Now, we are going to conditionally join the tips of both trees for the feature we are interested in. Connected tips will represent the same isolates.
green_tree <- dd1[which(dd1$Genotype == 'Green'), c('label', 'x', 'y', 'tree')] pp + geom_line(aes(x, y, group=label), data=green_tree, color='#009E73')