Birds are among the most adaptable and widespread tetrapods on Earth, thriving in environments from icy glaciers to arid deserts. One key to this success lies in the remarkable adaptability of their eggs, particularly the diverse structures of their eggshells. By exploring eggshell surface textures and patterns, researchers are uncovering how these features help birds survive and reproduce in such varied environments.
Evolution of Eggshell Diversity
The extraordinary diversity in bird species—over 10,000 worldwide—has resulted in a wide range of eggshell types, each adapted to specific environmental pressures. The surface structure of eggshells has evolved to meet different ecological needs, enhancing egg viability by regulating gas exchange, blocking harmful UV radiation, and preventing bacterial contamination. These features are especially crucial for birds that must breed in challenging environments, from freezing mountain peaks to arid desert landscapes.
Why Study Eggshell Surface Structure?
Most eggshell studies have focused on a handful of species, leaving gaps in our understanding of the full spectrum of eggshell variation and function. This study aimed to fill those gaps by analysing surface structure in around 450 bird species, randomly selected across the avian evolutionary tree. The objective was to capture as much diversity as possible and explore whether eggshell topography—its roughness, texture, and surface complexity—is shaped more by evolutionary relationships or by specific life-history traits like diet, nesting behaviour, and habitat.
Methods: Imaging Eggshell Texture in 3D
Researchers used cutting-edge imaging methods, including scanning electron microscopy and optical profilometry, to capture detailed, three-dimensional profiles of eggshell surfaces. These technologies allowed for precise measurements of surface roughness and structural complexity, even on very fine scales. The detailed 3D imaging revealed patterns in eggshell texture, such as rougher or more intricate surface structures, which could provide critical advantages for different species in managing gas exchange and protecting embryos from environmental threats.
Key Findings: Adaptations for Egg Viability
The study found that eggshell surfaces vary widely across species, often aligning with environmental factors:
- Environmental Protection: Rougher surfaces are common in eggs from dense habitats, such as forests, possibly aiding in moisture retention or deterring bacteria.
- UV Protection and Gas Exchange: Surface roughness and pigmentation patterns may help moderate UV exposure and regulate water vapour and gas diffusion, particularly in eggs laid in exposed or arid environments.
- Bacterial Defence: Textured surfaces may reduce bacterial movement, helping to prevent infection—a critical feature for eggs laid in humid or soil-rich areas.
Marie Attard 