Evolution of the courtship phenotype in the bird of paradise genus Parotia (Aves: Paradisaeidae): homology, phylogeny, and modularity

Birds of paradise (Aves: Paradisaeidae) exhibit extreme differences among taxa in courtship-related form (i.e. courtship phenotype). In the genus Parotia, the courtship phenotype is organizationally modular and this property may play an important role in the evolution of phenotypic disparity among taxa. The present study investigates variational aspects of phenotypic modularity in the Parotia by examining the structure and composition of courtship form in a comparative context. First, a module-based model of male display-phenotypes is compiled for four biological species to facilitate phenotypic comparison. Models are constructed using data from existing phenotype ontologies and associated video-vouchers. Next, a phylogenetic analysis of display-phenotype data is performed using a matrix of 47 etho-phenotypic characters coded for eight Parotia and out-group taxa. Analysis yields one tree, length 60 (CI = 0.83; RI = 0.85). The results demonstrate variation among taxa to be greater at higher-levels of phenotypic integration (i.e. among display-modules) than at intermediate and lower-levels (i.e. among phase- and element-modules). Three display-modules and five of six phase-modules were present in the common ancestor and complexity has increased through time as the display-modules became dissociated into subunits that diverged independently. The history of Parotia evolution involves numerous instances of duplication and divergence of etho-phenotypic modular components and likely reflects the same processes that have contributed to the pronounced phenotypic disparity within the entire bird of paradise radiation.