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

1Washington State University.
AJP Regulatory Integrative and Comparative Physiology (Impact Factor: 3.11). 09/2012; 303(9). DOI: 10.1152/ajpregu.00313.2012
Source: PubMed


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 (alpha) and synchronization to the daily light:dark cycle (phase angles) indirectly measured photoresponsiveness. Alpha 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 To test whether entrainment to non-photic cues superseded photic entrainment during the active season, bears were exposed to a reversed feeding regimen (dark-fed) under a natural photocycle.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.

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    • "The brown bear (Ursus arctos Linnaeus, 1758) is the largest member of Carnivora, and has a highly fragmented distribution across the Holarctic (Herrero, 1999; McLellan, Servheen & Huber, 2008). Declines in population over most of its range, increased conflict with people, and a need to make sound conservation decisions have led to numerous studies on conservation genetics, life-history traits, and behaviour in U. arctos (see Martin et al., 2010; Swenson, Taberlet & Bellemain, 2011; Deecke, 2012; Jasmine et al., 2012; Steyaert et al., 2012). A widespread range of modern populations and an increasing availability of ancient DNA samples (Barnes et al., 2002; Hofreiter et al., 2002, 2004; Miller, Waits & Joyce, 2006; Valdiosera et al., 2007, 2008; Calvignac et al., 2008; Bray et al., 2013) also make this species a useful model to study phylogeography in the Late Pleistocene–Holocene (Davison et al., 2011). "
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    ABSTRACT: The genetic diversity and phylogeography of maternal lineages in Ursus arctos Linnaeus, 1758 (the brown bear) have been studied extensively over the last two decades; however, sampling has largely been limited to the northern Holarctic, and was possibly biased towards lineages that recolonized the vast expanses of the north as the Last Glacial Maximum (LGM) ended. Here we report the genetic diversity and phylogeography of U. arctos from Turkey based on 35 non-invasive samples, including five from captive individuals. Bayesian phylogenetic analyses based on a 269-bp fragment of the mitochondrial DNA control region revealed 14 novel haplotypes belonging to three major lineages. The most widespread lineage was found to be the Eastern clade 3a, whereas geographically more restricted Western and Middle Eastern lineages were reported for the first time in Turkey. A specimen from the Taurus mountain range carried a haplotype closely related to the presumably extinct bears in Lebanon. Moreover, we identify a unique new lineage that appears to have split early within the Middle Eastern clade. Despite limited sampling, our study reveals a high level of mitochondrial diversity in Turkish U. arctos, shows that the ranges of both European and Middle Eastern clades extend into Turkey, and identifies a new divergent lineage of possibly wider historical occurrence. Obtaining these results with 35 samples also demonstrates the value of proper sampling from regions that have not been significantly affected by the LGM.
    Zoological Journal of the Linnean Society 08/2015; DOI:10.1111/zoj.12322 · 2.72 Impact Factor
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    • "Valencak, Tataruch & Ruf, 2009). On a finer scale, circadian rhythms of behaviour, such as the daily patterns of predator–prey interactions (Vidal et al., 2011), and of general activity (Iacarella & Helmuth, 2012; Ware et al., 2012), are generated endogenously, but are entrained by external abiotic factors: the two most important being the closely interrelated effects of light and temperature. Temperature has direct effects for ectotherms at all levels of organization, as metabolic reaction rates are intrinsically linked to temperature. "
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    ABSTRACT: In this study we investigated the environmental regulation of daily reproductive activity of guppies (Poecilia reticulata). We observed male guppy reproductive behaviour for 17 days over three time periods (dawn, noon, and dusk) while recording natural variation in water temperature and light level. Water temperatures recorded during the experiments were highly variable (up to 7 °C per day), and there was a recurring pattern in daily variation for both light and temperature. Levels of activity were highest at dawn and similarly low during noon and dusk, but reproductive behaviour was recorded throughout the day. Mixed-effects models indicate that light and temperature affect reproductive behaviour differently at different times of the day, and can also have opposing effects. We suggest that the environmental heterogeneity of streams in Trinidad has led to a broad thermal tolerance, and has contributed to the high level of phenotypic plasticity in the guppy and its success as an invasive species. Furthermore, our results show that daily variation in temperature and its interaction with light should be considered in future studies of guppy reproductive behaviour. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, ●●, ●●–●●.
    Biological Journal of the Linnean Society 03/2014; 111(3). DOI:10.1111/bij.12217 · 2.26 Impact Factor
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    • "However, the extremely small amplitude observed may be related to the unexpectedly small pineal gland in the bear. We hypothesize the very low nocturnal melatonin concentrations during the active season may facilitate a certain degree of behavioral flexibility allowing brown bears to adapt to highly variable food resources and diverse temporal niches (Ware et al. 2012). The elevated baseline melatonin during hibernation may be a unique adaptation in this large mammal to facilitate metabolic suppression by lowering body temperature and enhancing sleep propensity. "
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    ABSTRACT: Many temperate zone animals adapt to seasonal changes by altering their physiology. This is mediated in large part by endocrine signals that encode day length and regulate energy balance and metabolism. The objectives of this study were to determine if the daily patterns of two important hormones, melatonin and cortisol, varied with day length in captive brown bears (Ursus arctos) under anesthetized and nonanesthetized conditions during the active (March-October) and hibernation periods. Melatonin concentrations varied with time of day and season in nonanesthetized female bears despite exceedingly low nocturnal concentrations (1-4 pg/mL) in the active season. In contrast, melatonin concentrations during hibernation were 7.5-fold greater than those during the summer in anesthetized male bears. Functional assessment of the pineal gland revealed a slight but significant reduction in melatonin following nocturnal light application during hibernation, but no response to beta-adrenergic stimulation was detected in either season. Examination of pineal size in two bear species bears combined with a phylogenetically corrected analysis of pineal glands in 47 other species revealed a strong relationship to brain size. However, pineal gland size of both bear species deviated significantly from the expected pattern. Robust daily plasma cortisol rhythms were observed during the active season but not during hibernation. Cortisol was potently suppressed following injection with a synthetic glucocorticoid. The results suggest that melatonin and cortisol both retain their ability to reflect seasonal changes in day length in brown bears. The exceptionally small pineal gland in bears may be the result of direct or indirect selection.
    08/2013; 1(3):e00048. DOI:10.1002/phy2.48
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