title: Parsimony score of phylogenetic networks: hardness results and a linear-time heuristic.
abstract: Phylogenies-the evolutionary histories of groups of organisms-play a major role in representing the interrelationships among biological entities. Many methods for reconstructing and studying such phylogenies have been proposed, almost all of which assume that the underlying history of a given set of species can be represented by a binary tree. Although many biological processes can be effectively modeled and summarized in this fashion, others cannot: recombination, hybrid speciation, and horizontal gene transfer result in networks of relationships rather than trees of relationships. In previous works, we formulated a maximum parsimony (MP) criterion for reconstructing and evaluating phylogenetic networks, and demonstrated its quality on biological as well as synthetic data sets. In this paper, we provide further theoretical results as well as a very fast heuristic algorithm for the MP criterion of phylogenetic networks. In particular, we provide a novel combinatorial definition of phylogenetic networks in terms of "forbidden cycles," and provide detailed hardness and hardness of approximation proofs for the "small" MP problem. We demonstrate the performance of our heuristic in terms of time and accuracy on both biological and synthetic data sets. Finally, we explain the difference between our model and a similar one formulated by Nguyen et al., and describe the implications of this difference on the hardness and approximation results.
authors: Department of Computer Science, Rice University, Houston, TX 77005, USA. jin@cs.rice.edu
authors: Guohua
authors: G
authors: Jin
authors: Luay
authors: L
authors: Nakhleh
authors: Sagi
authors: S
authors: Snir
authors: Tamir
authors: T
authors: Tuller
mesh_terms: D000465:Algorithms; D001105:Archaea / Q000235:genetics; D051546:Cyclooxygenase 2 / Q000235:genetics; D008957:Models, Genetic; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D010944:Plants / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics
chemical_list: D010940:Plant Proteins; D012269:Ribosomal Proteins; D051546:Cyclooxygenase 2