Temporal organization of activity in the brown bear (Ursus arctos): roles of circadian rhythms, light, and food entrainment

Abstract

September 12, 2012; doi:10.1152/ajpregu.00313.2012.-Seasonal cycles of reproduction, migration, and hibernation are often synchronized to changes in daylength (photoperiod). Ecological and evolutionary pressures have resulted in physiological specializations enabling animals to occupy a particular temporal niche within the diel cycle leading to characteristic activity patterns. In this study, we characterized the annual locomotor activity of captive brown bears (Ursus arctos). Locomotor activity was observed in 18 bears of varying ages and sexes during the active (Mar-Oct) and hibernating (Nov-Feb) seasons. All bears exhibited either crepuscular or diurnal activity patterns. Estimates of activity duration (␣) and synchronization to the daily light:dark cycle (phase angles) indirectly measured photoresponsiveness. ␣ increased as daylength increased but diverged near the autumnal equinox. Phase angles varied widely between active and hibernating seasons and exhibited a clear annual rhythm. To directly test the role of photoperiod, bears were exposed to controlled photoperiod alterations. Bears failed to alter their daily activity patterns (entrain) to experimental photoperiods during the active season. In contrast, photic entrainment was evident during hibernation when the daily photocycle was shifted and when bears were exposed to a skeleton (11:1:11:1) photoperiod. To test whether entrainment to nonphotic cues superseded photic entrainment during the active season, bears were exposed to a reversed feeding regimen (dark-fed) under a natural photocycle. Activity shifted entirely to a nocturnal pattern. Thus daily activity in brown bears is highly modifiable by photoperiod and food availability in a stereotypic seasonal fashion. entrainment; food-entrainable oscillator; hibernation; phase shift; brown bear ACTIVITY PATTERNS are a useful behavioral measure to inform ecological and conservation studies. By examining these patterns, the impact of habitat destruction, food availability, and conspecific interactions can be revealed. Furthermore, a large body of literature has revealed that rather than merely being stimulated or suppressed by light and dark, many activity patterns are generated by a clock-like mechanism (17,60). This biological clock is highly conserved because it enables animals to accurately and reliably perform functions integral to survival due to the predictable nature of the earth's rotation and seasonal changes in daylength (5). The biological clock thus serves as both a timekeeper and calendar.Considerable research has characterized activity patterns of wild brown (Ursus arctos) and black bears (Ursus americanus), although much less is known about the physiological mechanisms that generate them. Both brown and black bears are capable of exhibiting a wide variety of activity patterns depending on season, geographic location, food availability, and human influences, just to name a few (22,27,34,41,49,54,77). Bears exhibit distinct seasonal timing of activities such as reproduction and hyperphagia ...

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Systemic effects of a high saturated fat diet in grizzly bears (Ursus arctos horribilis)

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A protocol for the isolation and cultivation of brown bear (Ursus arctos) adipocytes

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