Multi-SpaM: A maximum-likelihood approach to phylogeny reconstruction using multiple spaced-word matches and quartet trees

Word-based or ‘alignment-free’ methods for phylogeny reconstruction are much faster than traditional, alignment-based approaches, but they are generally less accurate. Most alignment-free methods calculate pairwise distances for a set of input sequences, for example from word frequencies, from so-called spaced-word matches or from the average length of common substrings. In this paper, we propose the first word-based phylogeny approach that is based on multiple sequence comparison and Maximum Likelihood. Our algorithm first samples small, gap-free alignments involving four taxa each. For each of these alignments, it then calculates a quartet tree and, finally, the program Quartet MaxCut is used to infer a super tree for the full set of input taxa from the calculated quartet trees. Experimental results show that trees calculated with our approach are of high quality.