Patterns of correlated character evolution in flightless birds: a phylogenetic approach

Abstract

Given a robust phylogeny for a particular higher taxon, it is possible to map the evolution of various character changes onto the phylogeny and study the extent to which they co-occur. Of particular interest are the questions of (a) whether particular morphological changes tend to accompany changes in ecology or behaviour to which they bear a functional relationship and (b) whether changes in those ‘primary’ morphological characters tend to be associated with correlated changes in other aspects of morphology, as would be expected given the high level of morphological integration that characterizes most organisms. Here we report a study of this kind, looking at morphological correlates of the evolution of flightlessness in birds, and using the concentrated changes test to determine whether associations are significant. We find that pectoral reduction, pelvic enlargement and changes in skull morphology significantly co-occur, and that these are usually achieved through heterochrony rather than other kinds of developmental reprogramming.