Roelof A. Hut Post-doc at the University of Groningen, Center of Behavioural Neurosciences, the Netherlands Title The ground squirrel and the sun; a story about diurnal adaptation and hibernation energetics Abstract Evolution of life on our planet has been under continuous influence of sunlight, and its daily and yearly incidence cycles caused by the earth´s axial rotation and solar orbit. Daily variation in sunlight intensity resulted in a circadian system to evolve in almost all known life forms. Such a system enabled the European ground squirrel to adopt an extremely diurnal activity pattern, partly to match its visual adaptations. A possible mechanism of such extreme entrainment is suggested and tested in Arctic ground squirrels living in the polar summer. Yearly variation in temperature causes ground squirrels to exhibit extreme physiological changes when they go into heterothermic, energy saving winter hibernation. Despite possible neurobiological consequences, hibernation seems to be beneficial for winter survival. However, detailed energetic models show that (with current reaction norms) it may eventually become mal-adaptive and a threat to the species when winter temperatures rise, as predicted by climate models showing global warming.   Biography 1993 Masters in Biology, University of Groningen Project title: “Energetics of hibernation in European ground squirrels” 2001 PhD in Biology, University of Groningen (promotor S.Daan) Project title: “Natural entrainment of circadian systems: a study in the European ground squirrel” 2000-2002 Marie Curie fellow at INSERM 371 (H.M.Cooper), Lyon, France Project title: “Photon integration in the circadian system” 2002-2005 NWO-Veni fellow at University of Groningen “Genes for Time: the role of clock genes in entrainment” Roelof A. Hut Rijksuniversiteit Groningen Basiseenheid Diergedag the Netherlands web: http://www.biol.rug.nl email: r.a.hut@biol.rug.nl