Volumetric analysis of brain structures, especially of the visual system in wild and domestic turkeys (Meleagris gallopavo).

The total brain volume, the volumes of the main brain subdivisions and regions belonging to the visual system of wild and domestic turkeys of either sex were measured and related to body weight. Using allometric methods sex-related reductions in brain size from wild to domesticated state was examined. Male domestic turkeys have 29% and female domestic turkeys 24% less brain volume. The total reduction of the brain size results from decreases of the brain subdivisions and structures of functional systems at various degree. The general reduction of prosencephalic brain parts is greater (males: 35%, females: 30%) than that of the rhombencephalon (males: 21%, females: 14%). Visual brain structures are reduced by 25% in males and 22% in females. The tertiary areas of this system have more decreased than secondary and primary visual targets. It was also shown that differences in size are accompanied by changes in the proportions of the brain. Telencephalic brain parts are relatively smaller in domestic turkeys. Different decreases in brain size of diverse species from wild to domestic state are regarded as processes of functional adaptation that is controlled by intensive breeding.