title: Is Beak Morphology in Darwin's Finches Tuned to Loading Demands?
abstract: One of nature's premier illustrations of adaptive evolution concerns the tight correspondence in birds between beak morphology and feeding behavior. In seed-crushing birds, beaks have been suggested to evolve at least in part to avoid fracture. Yet, we know little about mechanical relationships between beak shape, stress dissipation, and fracture avoidance. This study tests these relationships for Darwin's finches, a clade of birds renowned for their diversity in beak form and function. We obtained anatomical data from micro-CT scans and dissections, which in turn informed the construction of finite element models of the bony beak and rhamphotheca. Our models offer two new insights. First, engineering safety factors are found to range between 1 and 2.5 under natural loading conditions, with the lowest safety factors being observed in species with the highest bite forces. Second, size-scaled finite element (FE) models reveal a correspondence between inferred beak loading profiles and observed feeding strategies (e.g. edge-crushing versus tip-biting), with safety factors decreasing for base-crushers biting at the beak tip. Additionally, we identify significant correlations between safety factors, keratin thickness at bite locations, and beak aspect ratio (depth versus length). These lines of evidence together suggest that beak shape indeed evolves to resist feeding forces.
authors.affiliation: Laboratory of Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerpen, Belgium.
authors.forename: Joris
authors.initials: J
authors.lastname: Soons
authors.affiliation: Laboratory of Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerpen, Belgium; Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, 9000, Gent, Belgium.
authors.forename: Annelies
authors.initials: A
authors.lastname: Genbrugge
authors.affiliation: Department of Biology, 221 Morrill Science Center, University of Massachusetts, Amherst, Massachusetts, 01003, United States of America.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Podos
authors.affiliation: Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, 9000, Gent, Belgium.
authors.forename: Dominique
authors.initials: D
authors.lastname: Adriaens
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, 2610, Antwerpen, Belgium; Department of movement and sports sciences, University of Ghent, Watersportlaan 2, 9000, Gent, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Aerts
authors.affiliation: Laboratory of Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerpen, Belgium.
authors.forename: Joris
authors.initials: J
authors.lastname: Dirckx
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, 2610, Antwerpen, Belgium; Département d'Ecologie et de Gestion de la Biodiversité, Museum National d'Histoire Naturelle, 57 rue Cuvier, Case postale 55, 75231, Paris, Cedex 5, France.
authors.forename: Anthony
authors.initials: A
authors.lastname: Herrel
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001502:Beak / Q000033:anatomy & histology* / Q000502:physiology; D005075:Biological Evolution; D046369:Finches / Q000033:anatomy & histology / Q000235:genetics*