Morphological Datasets Fit a Common Mechanism Much More Poorly than DNA Sequences and Call Into Question the Mkv Model

GOLOBOFF, PABLO A.; PITTMAN, MICHAEL; POL, DIEGO; XU, XING

SYSTEMATIC BIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2018

1063-5157

The Mkv evolutionary model, based on minor modifications to models ofmolecular evolution, is being increasingly used to infer phylogenies fromdiscrete morphological data, often producing different results fromparsimony.  The critical differencebetween Mkv and parsimony is the assumption of a ?common mechanism? in the Mkvmodel, with branch lengths determining that probability of change for allcharacters increases or decreases at the same tree branches by the sameexponential factor.  We evaluate whetherthe assumption of a common mechanism applies to morphology, by testing theprediction implicit in the Mkv model that branch lengths calculated fromdifferent subsets of characters will be significantly correlated.  Our analysis shows that DNA (38 datasetstested) is often compatible with a common mechanism, but morphology (86datasets tested) generally is not, showing very disparate branch lengths fordifferent character partitions.  The lowlevels of branch length correlation demonstrated for morphology (fitting modelswithout a common mechanism) suggest that the Mkv model is too unrealistic forthe analysis of morphological datasets.