Consensus Networks: A Method for Visualising Incompatibilities in Collections of Trees

We present a method for summarising collections of phylogenetic trees that extends the notion of consensus trees. Each branch in a phylogenetic tree corresponds to a bipartition or split of the set of taxa labelling its leaves. Given a collection of phylogenetic trees, each labelled by the same set of taxa, all those splits that appear in more than a predefined threshold proportion of the trees are displayed using a median network. The complexity of this network is bounded as a function of the threshold proportion. We demonstrate the method for a collection of 5000 trees resulting from a Monte Carlo Markov Chain analysis of 37 mammal mitochondrial genomes, and also for a collection of 80 equally parsimonious trees resulting from a heuristic search on 53 human mitochondrial sequences.