title: Latitudinal clines: an evolutionary view on biological rhythms.
abstract: Properties of the circadian and annual timing systems are expected to vary systematically with latitude on the basis of different annual light and temperature patterns at higher latitudes, creating specific selection pressures. We review literature with respect to latitudinal clines in circadian phenotypes as well as in polymorphisms of circadian clock genes and their possible association with annual timing. The use of latitudinal (and altitudinal) clines in identifying selective forces acting on biological rhythms is discussed, and we evaluate how these studies can reveal novel molecular and physiological components of these rhythms.
authors.affiliation: Chronobiology unit, Centre for Behaviour and Neuroscience, University of Groningen, Groningen, The Netherlands. r.a.hut@rug.nl
authors.forename: Roelof A
authors.initials: RA
authors.lastname: Hut
authors.forename: Silvia
authors.initials: S
authors.lastname: Paolucci
authors.forename: Roi
authors.initials: R
authors.lastname: Dor
authors.forename: Charalambos P
authors.initials: CP
authors.lastname: Kyriacou
authors.forename: Serge
authors.initials: S
authors.lastname: Daan
mesh_terms: D000531:Altitude; D000818:Animals; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology; D005075:Biological Evolution; D057906:Circadian Clocks / Q000235:genetics / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D007313:Insecta / Q000235:genetics / Q000502:physiology; D017440:Photoperiod; D011110:Polymorphism, Genetic; D012621:Seasons; D014714:Vertebrates / Q000235:genetics / Q000502:physiology
keywords: circadian; circannual; diapause; latitude; photoperiod; reproduction