title: Circadian rhythms in diving behavior and ventilatory response to asphyxia in canvasback ducks.
abstract: Underwater feeding behavior was measured in 10 captive canvasback ducks (Aythya valisineria) for 12 days under a 12:12-h light-dark photoperiod. Feeding activity exhibited a daily rhythm, with 76% of dives occurring at night. In separate experiments on six of these ducks, a circadian rhythm was observed in the duration of voluntary dives. Dives at night (14.7 +/- 0.7 s) were significantly longer than those during the day (10.7 +/- 0.7 s). These day-night differences in diving behavior were accompanied by day-night differences in respiratory responses to progressive asphyxia. In the same six ducks, ventilation increased exponentially as a function of inspired CO2 concentration during rebreathing in a closed-circuit barometric plethysmograph. The exponential rate constant for inspired ventilation was significantly smaller at night (0.23 +/- 0.02) than during the day (0.26 +/- 0.01). We suggest that intermittent apneic exercise is facilitated by reduced respiratory chemosensitivity and that the respiratory and behavioral control systems are synchronized by the circadian timing system in diving ducks.
authors.affiliation: Department of Zoology, University of Toronto, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Woodin
authors.forename: R
authors.initials: R
authors.lastname: Stephenson
mesh_terms: D000818:Animals; D001237:Asphyxia / Q000503:physiopathology; D001831:Body Temperature; D002940:Circadian Rhythm; D004242:Diving / Q000502:physiology*; D004372:Ducks / Q000502:physiology*; D005260:Female; D008168:Lung / Q000502:physiology; D008297:Male; D008433:Mathematics; D010991:Plethysmography; D012119:Respiration