title: Variability of behavioral chronotypes of 16 mammalian species under controlled conditions.
abstract: Human chronotypes (differences in preference for early or late rising each day) have been extensively studied in recent years, but no attempt has been made to compare human chronotypes with the chronotypes of other animal species. We evaluated behavioral chronotypes in 16 mammalian species along a body size gradient of five orders of magnitude (from mice to cattle). Individuals of all species were studied under a 12L:12D photoperiod in a thermoneutral environment with food and water available at all times. Rhythms of locomotor activity were analyzed for onset time, acrophase, and robustness. Neither of these rhythmic parameters was significantly related to body size, but onset time and acrophase varied considerably from species to species, thus characterizing diurnal and nocturnal species. Chronotype spreads ranged from less than an hour in sheep to almost 24h in cats, thus extending both below and above the human chronotype spread of 6h. The variability of chronotype (as quantified by the standard deviation of group means) was much larger between species than within species and also larger between individuals of a species than within individuals on consecutive days. These results help situate the matter of human chronotypes within the broader context of variability in the phase angle of entrainment of circadian rhythms in animals.
authors.affiliation: Circadian Rhythm Laboratory, Department of Psychology, Boise State University, Boise, ID 83725, USA. Electronic address: refinetti@circadian.org.
authors.forename: Roberto
authors.initials: R
authors.lastname: Refinetti
authors.affiliation: Biology Department, Siena Heights University, Adrian, MI 49221, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wassmer
authors.affiliation: Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
authors.forename: Priyoneel
authors.initials: P
authors.lastname: Basu
authors.affiliation: Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Cherukalady
authors.affiliation: Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
authors.forename: Varun Kumar
authors.initials: VK
authors.lastname: Pandey
authors.affiliation: Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
authors.forename: Muniyandi
authors.initials: M
authors.lastname: Singaravel
authors.affiliation: Laboratorio di Cronofisiologia Veterinaria, Dipartimento di Scienze Veterinarie, Università degli Studi di Messina, 98168 Messina, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Giannetto
authors.affiliation: Laboratorio di Cronofisiologia Veterinaria, Dipartimento di Scienze Veterinarie, Università degli Studi di Messina, 98168 Messina, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Piccione
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008322:Mammals / Q000502:physiology*; D017440:Photoperiod; D013045:Species Specificity
keywords: Chronotype; Circadian rhythm; Intersubject variability; Intrasubject variability; Locomotor activity