FINDING OPTIMAL INGROUP TOPOLOGIES AND CONVEXITIES WHEN THE CHOICE OFOUTGROUPS IS NOT OBVIOUS

Considerable confusion remains among theoreticians and practicioners o f phylogenetic science on the use of outgroup taxa. Here, we show that , despite claims to the contrary, details of the optimal ingroup topol ogy can be changed by switching outgroup taxa. This has serious implic ations for phylogenetic accuracy. We delineate between the process of outgroup selection and the various possible processes involved in usin g an outgroup taxon after one has been selected. Criteria are needed f or the determination that particular outgroup taxa do not reduce the a ccuracy of evolutionary tree topologies and inferred character state t ransformations. We compare previous results from a sensitivity bootstr ap analysis of the mitochondrial cytochrome b phylogenetic relationshi ps among whales to the results of a Bremer support sensitivity analysi s and of a recently developed application of RASA theory to the questi on of putative outgroup taxon plesiomorphy content. (C) 1998 Academic Press.