title: Adaptive evolution of a derived radius morphology in manakins (Aves, Pipridae) to support acrobatic display behavior.
abstract: The morphology of the avian skeleton is often studied in the context of adaptations for powered flight. The effects of other evolutionary forces, such as sexual selection, on avian skeletal design are unclear, even though birds produce diverse behaviors that undoubtedly require a variety of osteological modifications. Here, we investigate this issue in a family of passerine birds called manakins (Pipridae), which have evolved physically unusual and elaborate courtship displays. We report that, in species within the genus Manacus, the shaft of the radius is heavily flattened and shows substantial solidification. Past work anecdotally notes this morphology and attributes it to the species' ability to hit their wings together above their heads to produce loud mechanical sonations. Our results show that this feature is unique to Manacus compared to the other species in our study, including a variety of taxa that produce other sonations through alternate wing mechanisms. At the same time, our data reveal striking similarities across species in total radius volume and solidification. Together, this suggests that supposedly adaptive alterations in radial morphology occur within a conserved framework of a set radius volume and solidness, which in turn is likely determined by natural selection. Further allometric analyses imply that the radius is less constrained by body size and the structural demands that underlie powered flight, compared to other forelimb bones that are mostly unmodified across taxa. These results are consistent with the idea that the radius is more susceptible to selective modification by sexual selection. Overall, this study provides some of the first insight into the osteological evolution of passerine birds, as well as the way in which opposing selective forces can shape skeletal design in these species. J. Morphol. 277:766-775, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California, 90095.
authors.forename: Anthony
authors.initials: A
authors.lastname: Friscia
authors.affiliation: Department of Biology, Wake Forest University, Winston-Salem, North Carolina, 27109.
authors.forename: Gloria D
authors.initials: GD
authors.lastname: Sanin
authors.affiliation: Department of Biological and Environmental Sciences, Gothenburg University, Gothenburg, Sweden.|Department of Biology, University of Mississippi, University, Mississippi, 38677.
authors.forename: Willow R
authors.initials: WR
authors.lastname: Lindsay
authors.affiliation: Department of Biology, University of Mississippi, University, Mississippi, 38677.
authors.forename: Lainy B
authors.initials: LB
authors.lastname: Day
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California, 90095.|Laboratory of Neuroendocrinology, University of California, Los Angeles, California, 90095.|Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, 90095.|Smithsonian Tropical Research Institute, Balboa, Ancon, Panama.
authors.forename: Barney A
authors.initials: BA
authors.lastname: Schlinger
authors.affiliation: Department of Radiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, 27157.
authors.forename: Josh
authors.initials: J
authors.lastname: Tan
authors.affiliation: Department of Biology, Wake Forest University, Winston-Salem, North Carolina, 27109.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Fuxjager
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001522:Behavior, Animal; D005075:Biological Evolution; D003380:Courtship; D021621:Imaging, Three-Dimensional; D009929:Organ Size; D046109:Passeriformes / Q000033:anatomy & histology*; D011884:Radius / Q000033:anatomy & histology*; D012044:Regression Analysis
keywords: avian skeleton; courtship display; manakin; passerine bird; sexual selection