Adaptive variation in avian eggshell gas conductance and structure across elevational gradients?

Abstract
Data availability
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Abstract

Many tropical bird species have restricted elevational distributions, potentially limited by how environmental conditions affect physiological processes. While some studies have examined adult physiology across elevations, relatively little attention has been given to the structure and function of eggshells despite their critical role in regulating gas exchange during the vulnerable embryonic stage. At high elevations, dry air is expected to increase water loss from the egg, and natural selection may favor lower gas conductance to reduce desiccation risk. Structural variation in eggshells, such as increased shell thickness or reduced pore size and density, could serve as a mechanism to regulate gas diffusion. To test for adaptive variation in eggshell traits along elevational gradients, we measured water vapor conductance and used scanning electron microscopy (SEM) to examine eggshell structure in 197 bird species from the Andes. We found that water vapor conductance declined at high elevations across avian communities. However, structural changes in eggshells varied among bird families and did not vary in a predictable way with elevation, suggesting no relationship or divergent adaptive responses to shared selective pressures, particularly in shell thickness, pore density, and pore size. We propose that examining functional and structural eggshell traits can offer insight into species' elevational limits and inform predictions about their responses to climate change.

Data availability

Data and code for this paper are available in the Figshare Digital Repository: 10.6084/m9.figshare.30182047

The following data sets were generated

1. Ocampo D
2. et al
(2025) Adaptive variation in avian eggshell gas conductance and structure across elevational gradients?
Figshare, 10.6084/m9.figshare.30182047.

https://figshare.com/articles/dataset/_b_Adaptive_variation_in_avian_eggshell_b_-_b_Data_accessibility_b_/30182047

Article and author information

Author details

David Ocampo

Department of Ecology and Evolutionary Biology, Princeton University, Princeton, United States

For correspondence
docampo@princeton.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0003-1597-4038
Carlos D Cadena

Departamento de Ciencias Biológicas, Universidad de Los Andes, Bogotá, Colombia

Competing interests
The authors declare that no competing interests exist.
Esteban Correa-Agudelo

Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, United States

Competing interests
The authors declare that no competing interests exist.
Marcela Hernández Hoyos

Departamento de Ingeniería de Sistemas y Computación, Univesidad de los Andes, Bogotá, Colombia

Competing interests
The authors declare that no competing interests exist.
Gustavo A. Londoño

Departamento de Ciencias Biológicas, Universidad Icesi, Cali, Colombia

For correspondence
galondono@icesi.edu.co

Competing interests
The authors declare that no competing interests exist.

Funding

National Science Foundation (DEB-1120682)

Gustavo A. Londoño

Neotropical Ornithological Society (Francois Vuilleumier Fund)

David Ocampo

American Ornithologists' Union (Research Grant)

David Ocampo

National Museum of Natural History (Graduate Student Fellowships)

David Ocampo

Association of Field Ornithologists (Alexander Skutch Award)

Gustavo A. Londoño

Wilson Ornithological Society (Louis Agassiz Fuertes Award)

Gustavo A. Londoño

American Ornithologists' Union (Alexander Wetmore Award)

Gustavo A. Londoño

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: Our animal use protocols were approved by the University of Florida IACUC (Protocol #201106068). Field research in Peru was authorized by Conservación Amazónica ACCA and conducted under permits from the Government of Peru (Permit 0239-2013 MINAGRI-DGFFS/DGEFFS). In Colombia, protocols were approved by Universidad Icesi and authorized by ANLA (Resolution #0509, 21 May 2014). To minimize potential impacts on nesting performance, we restricted our sampling to eggs from nests with known clutch age that were either abandoned or partially predated.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.