Seasonal Clock of Siberian Hamsters (IMAGE) University of Chicago Caption Siberian hamsters exhibit striking seasonal changes in physiology and behavior, which are driven by epigenetic changes in gene expression in the brain, as revealed in new research appearing this week in the online Early Edition of the Proceedings of the National Academy of Sciences. The hamster on the left is in the summer breeding condition, whereas the hamster on the right is in the winter non-breeding condition. Credit Tyler Stevenson Usage Restrictions News organizations may use this image in connection with reports about the research of Brian Prendergrast and Tyler Stevenson. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.