DOES LEKKING PROMOTE THE EVOLUTION OF MALE-BIASED SIZE DIMORPHISM IN BIRDS - ON THE USE OF COMPARATIVE APPROACHES

An early study compared the size dimorphism of lekking and nonlekking birds by out-group analysis (i.e., evolutionarily independent clades) and could not find, contrary to common belief, that lekking birds were more size dimorphic than their close relatives. A subsequent study reanalyzed the data using different comparative approaches and did find the postulated relationship. This study compared the generic means of sister taxa that differ in mating system (lekking vs. nonlekking) and analyzed concentrations of size dimorphism and lekking in a reconstruction of the bird phylogeny. In the present article we have once again reanalyzed the data and extended the comparative analyses. We find no evidence that lekking birds show more size dimorphism when compared to their close relatives and argue that the result of the second study can be explained mainly by the inclusion or exclusion of taxa and a bias introduced by a few clades in which size dimorphism indeed is larger in the lekking taxa. However, when independent evolutionary events are analyzed, lekking does not seem to promote the evolution of male-biased size dimorphism.