CHICAGO, Feb. 14 (Xinhua) -- A study of the University of Illinois (UI) links fox domestication to changes in gene activity in the pituitary gland, a brain center that kicks out hormones to regulate various bodily functions, including the stress response.

To get a better view of how this occurs, the researchers looked at gene activity in the anterior pituitary glands of foxes in a breeding program at the Institute of Cytology and Genetics in Novosibirsk, Russia, designed to study the evolutionary processes associated with domestication. They compared six foxes selectively bred for tameness and six foxes selectively bred for aggression.

And analysis revealed that the differences between tame and aggressive foxes may lie in cells in the anterior pituitary gland, which can change their shapes to communicate with one another about when it's time to release stress hormones.

As previous studies show that ACTH levels in the anterior pituitary do not differ between tame and aggressive fox strains, researchers hold that the pituitary glands of tame fox strain may produce the same amount of stress hormones but be less efficient at getting those hormones into the bloodstream.

"If confirmed, our finding could help explain why tame foxes are not stressed so easily as foxes that have not been selected for tameness," said UI animal sciences professor Anna Kukekova.

The study, published in the journal G3: Genes, Genomes, Genetics, has added to a growing body of evidence suggesting that domestication alters animals' reactivity to stress.