title: Cranial shape evolution in adaptive radiations of birds: comparative morphometrics of Darwin's finches and Hawaiian honeycreepers.
abstract: Adaptive radiation is the rapid evolution of morphologically and ecologically diverse species from a single ancestor. The two classic examples of adaptive radiation are Darwin's finches and the Hawaiian honeycreepers, which evolved remarkable levels of adaptive cranial morphological variation. To gain new insights into the nature of their diversification, we performed comparative three-dimensional geometric morphometric analyses based on X-ray microcomputed tomography (µCT) scanning of dried cranial skeletons. We show that cranial shapes in both Hawaiian honeycreepers and Coerebinae (Darwin's finches and their close relatives) are much more diverse than in their respective outgroups, but Hawaiian honeycreepers as a group display the highest diversity and disparity of all other bird groups studied. We also report a significant contribution of allometry to skull shape variation, and distinct patterns of evolutionary change in skull morphology in the two lineages of songbirds that underwent adaptive radiation on oceanic islands. These findings help to better understand the nature of adaptive radiations in general and provide a foundation for future investigations on the developmental and molecular mechanisms underlying diversification of these morphologically distinguished groups of birds.This article is part of the themed issue 'Evo-devo in the genomics era, and the origins of morphological diversity'.
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA tokkyevolution@gmail.com.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tokita
authors.affiliation: Department of Oral Anatomy, Asahi University School of Dentistry, 1851 Hozumi, Mizuho, Gifu 501-0296, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Yano
authors.affiliation: Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, MRC 116, Washington, DC 20013-7012, USA.
authors.forename: Helen F
authors.initials: HF
authors.lastname: James
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA a.aabzhanov@imperial.ac.uk.
authors.forename: Arhat
authors.identifier: 0000-0002-8577-8318
authors.initials: A
authors.lastname: Abzhanov
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D046369:Finches / Q000033:anatomy & histology; D008297:Male; D046109:Passeriformes / Q000033:anatomy & histology*; D012886:Skull / Q000033:anatomy & histology*; D055114:X-Ray Microtomography
keywords: Darwin's finches; Hawaiian honeycreepers; adaptive radiation; geometric morphometrics; skull shape