Birds, Geometric morphometrics, Allometry, Integration, Feeding, Parrots
Digital Object Identifier (DOI)
Background: The Psittaciformes (parrots and cockatoos) are characterised by their large beaks, and are renowned for their ability to produce high bite forces. These birds also possess a suite of modifications to their cranial architecture interpreted to be adaptations for feeding on mechanically resistant foods, yet the relationship between cranial morphology and diet has never been explicitly tested. Here, we provide a three-dimensional geometric morphometric analysis of the developmental and biomechanical factors that may be influencing the evolution of psittaciformes’ distinctive cranial morphologies.
Results: Contrary to our own predictions, we find that dietary preferences for more- or less- mechanically resistant foods have very little influence on beak and skull shape, and that diet predicts only 2.4% of the shape variation in psittaciform beaks and skulls. Conversely, evolutionary allometry and integration together predict almost half the observed shape variation, with phylogeny remaining an important factor in shape identity throughout our analyses, particularly in separating cockatoos (Cacatuoidea) from the true parrots (Psittacoidea).
Conclusions: Our results are similar to recent findings about the evolutionary trajectories of skull and beak shape in other avian families. We therefore propose that allometry and integration are important factors causing canalization of the avian head, and while diet clearly has an influence on beak shape between families, this may not be as important at driving evolvability within families as is commonly assumed.
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Citation / Publisher Attribution
BMC Evolutionary Biology, v. 19, art. 104
Scholar Commons Citation
Bright, Jen A.; Marugán-Lobón, Jesús; Rayfield, Emily J.; and Cobb, Samuel N., "The Multifactorial Nature of Beak and Skull Shape Evolution in Parrots and Cockatoos (Psittaciformes)" (2019). School of Geosciences Faculty and Staff Publications. 2160.
Amination cycling between maximum and minimum warps of PC1, scale factor = 1. Warp template is based on a CT scan of Conuropsis carolinensis. (GIF 1082 kb)
Additional File 2.gif (987 kB)
Animation cycling between maximum and minimum warps of PC2, scale factor = 1. Warp template is based on a CT scan of Conuropsis carolinensis. (GIF 987 kb)
Additional File 3.gif (929 kB)
Animation cycling between maximum and minimum warps of PC3, scale factor = 1. Warp template is based on a CT scan of Conuropsis carolinensis. (GIF 929 kb)
Additional File 4.docx (1620 kB)
Supplementary figures and tables. (DOCX 1620 kb)
Additional File 5.pdf (33801 kB)
Interactive 3D visualisations of the maximum and minimum warps along PCs 1–3. Warp template is based on a CT scan of Conuropsis carolinensis. (PDF 33801 kb)
Additional File 6.zip (2110 kB)
Zipped folder containing supplementary data files and code. BrightetalParrotsGM.R: R script used for running analysis. R input data: Ccarolinensis.ply; EltonTraits1.csv; landpairs.txt; NewParrots.tre; parrot.lms.txt; Parrot_preSlide.txt; ParrotGroups.csv; sliders.txt. (ZIP 2110 kb)