DOI: 10.1080/10635150590923227 A New Technique for Identifying Sequence Heterochrony

Abstract.—Sequence heterochrony (changes in the order in which events occur) is a potentially important, but relatively poorly explored, mechanism for the evolution of development. In part, this is because of the inherent difficulties in inferring sequence heterochrony across species. The event-pairing method, developed independently by several workers in the mid-1990s, encodes sequences in a way that allows them to be examined in a phylogenetic framework, but the results can be difficult to interpret in terms of actual heterochronic changes. Here, we describe a new, parsimony-based method to interpret such results. For each branch of the tree, it identifies the least number of event movements (heterochronies) that will explain all the observed event-pair changes. It has the potential to find all alternative, equally parsimonious explanations, and generate a consensus, containing the movements that form part of every equally most parsimonious explanation. This new technique, which we call Parsimov, greatly increases the utility of the event-pair method for inferring instances of sequence heterochrony. [Developmental sequences; event pairing; heterochrony; Parsimov program; principle of parsimony.] Developmental data from temporal sequences, espe-cially those in embryonic development, are increasingly being analyzed in an evolutionary context (e.g., Mabe