title: Shared developmental programme strongly constrains beak shape diversity in songbirds.
abstract: The striking diversity of bird beak shapes is an outcome of natural selection, yet the relative importance of the limitations imposed by the process of beak development on generating such variation is unclear. Untangling these factors requires mapping developmental mechanisms over a phylogeny far exceeding model systems studied thus far. We address this issue with a comparative morphometric analysis of beak shape in a diverse group of songbirds. Here we show that the dynamics of the proliferative growth zone must follow restrictive rules to explain the observed variation, with beak diversity constrained to a three parameter family of shapes, parameterized by length, depth and the degree of shear. We experimentally verify these predictions by analysing cell proliferation in the developing embryonic beaks of the zebra finch. Our findings indicate that beak shape variability in many songbirds is strongly constrained by shared properties of the developmental programme controlling the growth zone.
authors.affiliation: 1] School of Engineering and Applied Sciences and Kavli Institute for Bionano Science and Technology, Harvard University, Cambridge, Massachusetts 02138, USA [2].
authors.forename: Joerg A
authors.initials: JA
authors.lastname: Fritz
authors.affiliation: 1] Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA [2].
authors.forename: Joseph
authors.initials: J
authors.lastname: Brancale
authors.affiliation: 1] Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA [2].
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tokita
authors.affiliation: Department of Biology, San Diego State University, San Diego, California 92182, USA.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Burns
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: M Brent
authors.initials: MB
authors.lastname: Hawkins
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Arhat
authors.initials: A
authors.lastname: Abzhanov
authors.affiliation: School of Engineering and Applied Sciences and Kavli Institute for Bionano Science and Technology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Brenner
mesh_terms: D000818:Animals; D001502:Beak / Q000033:anatomy & histology / Q000196:embryology*; D001837:Body Weights and Measures; D049109:Cell Proliferation; D003198:Computer Simulation; D046369:Finches / Q000033:anatomy & histology / Q000196:embryology*; D008954:Models, Biological; D009024:Morphogenesis / Q000502:physiology*; D010802:Phylogeny; D012641:Selection, Genetic