Colorings of unrooted tree-based networks and related graphs

In mathematical phylogenetics, evolutionary relationships are often represented by trees and networks.

The latter are typically used whenever the relationships cannot be adequately described by a tree, which happens when reticulate evolutionary events happen, such as horizontal gene transfer or hybridization.

But as such events are known to be relatively rare for most species, evolution is sometimes thought of as a process that can be represented by a tree with some additional edges, i.e., with a network that is still "somewhat tree-like".

In this context, different versions of tree-based networks have played a major role in recent phylogenetic literature.

Yet, surprisingly little is known about their combinatorial and graph-theoretic properties.

In our manuscript, we answer a recently published question concerning the colorability of a specific class of tree-based networks.

In particular, we will investigate an even more general class of graphs and show their 3-colorability.

This nicely links recent phylogenetic concepts with classical graph theory.

Moreover, the ideas we use to answer the colorability question are new and might potentially be generalizable to other coloring problems in graph theory.