title: The evolution of eggshell cuticle in relation to nesting ecology.
abstract: Avian eggs are at risk of microbial infection prior to and during incubation. A large number of defence mechanisms have evolved in response to the severe costs imposed by these infections. The eggshell's cuticle is an important component of antimicrobial defence, and its role in preventing contamination by microorganisms in domestic chickens is well known. Nanometer-scale cuticular spheres that reduce microbial attachment and penetration have recently been identified on eggs of several wild avian species. However, whether these spheres have evolved specifically for antimicrobial defence is unknown. Here, we use comparative data on eggshell cuticular structure and nesting ecology to test the hypothesis that birds nesting in habitats with higher risk of infection (e.g. wetter and warmer) are more likely to evolve cuticular nanospheres on their eggshells than those nesting in less risky habitats. We found that nanostructuring, present in 54 of 296 analysed species, is the ancestral condition of avian eggshells and has been retained more often in taxa that nest in humid infection-prone environments, suggesting that they serve critical roles in antimicrobial egg defence.
authors.affiliation: Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH 44325-3908, USA Department of Biology, Terrestrial Ecology Unit, University of Ghent, 9000 Ghent, Belgium liliana.dalba@ugent.be.
authors.forename: Liliana
authors.identifier: 0000-0002-2478-3455
authors.initials: L
authors.lastname: D'Alba
authors.affiliation: Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY 10027, USA.
authors.forename: Rafael
authors.identifier: 0000-0002-7563-9795
authors.initials: R
authors.lastname: Maia
authors.affiliation: Department of Psychology, Hunter College and the Graduate Center, City University of New York, New York, NY 10065, USA.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Hauber
authors.affiliation: Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH 44325-3908, USA Department of Biology, Terrestrial Ecology Unit, University of Ghent, 9000 Ghent, Belgium.
authors.forename: Matthew D
authors.identifier: 0000-0002-5131-8209
authors.initials: MD
authors.lastname: Shawkey
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000145:classification; D060467:Disease Resistance; D004463:Ecology; D017753:Ecosystem; D004528:Egg Shell / Q000502:physiology*; D010802:Phylogeny
keywords: eggshell cuticle; microbial infection; nest humidity; nest type