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Type: Journal article
Title: Variability in avian eggshell colour: a comparative study of museum eggshells
Author: Cassey, P.
Portugal, S.
Maurer, G.
Ewen, J.
Boulton, R.
Hauber, M.
Blackburn, T.
Citation: PLoS One, 2010; 5(8):e12054
Publisher: Public Library of Science
Issue Date: 2010
ISSN: 1932-6203
Statement of
Phillip Cassey, Steven J. Portugal, Golo Maurer, John G. Ewen, Rebecca L. Boulton, Mark E. Hauber and Tim M. Blackburn
Abstract: Background: The exceptional diversity of coloration found in avian eggshells has long fascinated biologists and inspired a broad range of adaptive hypotheses to explain its evolution. Three main impediments to understanding the variability of eggshell appearance are: (1) the reliable quantification of the variation in eggshell colours; (2) its perception by birds themselves, and (3) its relation to avian phylogeny. Here we use an extensive museum collection to address these problems directly, and to test how diversity in eggshell coloration is distributed among different phylogenetic levels of the class Aves. Methodology and Results: Spectrophotometric data on eggshell coloration were collected from a taxonomically representative sample of 251 bird species to determine the change in reflectance across different wavelengths and the taxonomic level where the variation resides. As many hypotheses for the evolution of eggshell coloration assume that egg colours provide a communication signal for an avian receiver, we also modelled reflectance spectra of shell coloration for the avian visual system. We found that a majority of species have eggs with similar background colour (long wavelengths) but that striking differences are just as likely to occur between congeners as between members of different families. The region of greatest variability in eggshell colour among closely related species coincided with the medium-wavelength sensitive region around 500 nm. Conclusions: The majority of bird species share similar background eggshell colours, while the greatest variability among species aligns with differences along a red-brown to blue axis that most likely corresponds with variation in the presence and concentration of two tetrapyrrole pigments responsible for eggshell coloration. Additionally, our results confirm previous findings of temporal changes in museum collections, and this will be of particular concern for studies testing intraspecific hypotheses relating temporal patterns to adaptation of eggshell colour. We suggest that future studies investigating the phylogenetic association between the composition and concentration of eggshell pigments, and between the evolutionary drivers and functional impacts of eggshell colour variability will be most rewarding.
Keywords: Egg Shell; Animals; Birds; Pigmentation; Spectrophotometry; Adaptation, Physiological; Evolution, Molecular; Phylogeny; Species Specificity; Light; Museums
Rights: © 2010 Cassey et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
RMID: 0020108031
DOI: 10.1371/journal.pone.0012054
Appears in Collections:Earth and Environmental Sciences publications
Environment Institute Leaders publications

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