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Variation in avian brain shape: relationship with size and orbital shape
Soichiro Kawabe1, Tetsuya Shimokawa, Hitoshi Miki
1The University Museum, The University of Tokyo, Tokyo, Japan; Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan; Gifu Prefectural Museum, Gifu, Japan.
Journal of Anatomy
|September 12, 2013
Summary
Bird brain shape varies significantly, influenced by brain size and orbital shape. Understanding these three-dimensional (3D) geometric relationships is key to avian evolution.
Area of Science:
- Comparative anatomy
- Evolutionary biology
- Neuroscience
Background:
- Avian brain shape exhibits considerable diversity, reflecting evolutionary adaptations.
- Previous research primarily used volumetric or linear measurements, limiting 3D geometric insights.
- Understanding avian brain evolution necessitates quantitative analysis of 3D geometry.
Purpose of the Study:
- To investigate the relationship between overall brain size and avian brain shape.
- To examine the correlation between avian brain shape and orbital shape.
- To explore the 3D geometric morphometrics of avian brains.
Main Methods:
- Reconstruction of avian brain endocasts from computed tomography (CT) images.
- Analysis using 3D geometric morphometrics and principal component analysis (PCA).
- Multivariate regression and two-block partial least-squares (PLS) analyses to assess shape correlations.
Main Results:
- PCA identified significant regional variations and shape correlations between brain regions (telencephalon, cerebellum, myelencephalon, diencephalon, optic tectum).
- Increased brain size correlated with a more slender telencephalon and altered brain orientation.
- Brain shape correlated with orbital shape: rounder orbits associated with rounder brains and ventrally flexed bases, while elongated orbits linked to narrower brains and flatter bases.
Conclusions:
- Functionally linked avian brain regions exhibit correlated shapes.
- Orbital size and shape are significant determinants of overall avian brain geometry.
- This study provides novel 3D geometric insights into avian brain evolution and adaptation.
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