Circannual rhythmicity in a non-hibernating ground squirrel, Citellus leucurus

Pengelley, Eric T.; Asmundson, Sally J.; Aloia, Roland C.; Barnes, Brian M.

doi:10.1016/s0300-9629(76)80103-x

Cited by 9 publications

(2 citation statements)

References 19 publications

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“…This idea has been proposed on theoretical grounds (e.g. Pengelley 1968;Pengelley et al 1976;) and has recently found empirical support in studies of mammalian circannual rhythms (Lincoln et al 2006). Lincoln and colleagues described the occurrence of free-running circannual rhythms driven by a pacemaker that is separate from the regulation of reproductive activity by studying prolactin rhythms in sheep.…”

Section: (D) Proximate Mechanisms Underlying Circannual Rhythmsmentioning

confidence: 96%

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Wikelski

Martin

Scheuerlein

et al. 2007

Phil. Trans. R. Soc. B

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Endogenous circannual clocks are found in many long-lived organisms, but are best studied in mammal and bird species. Circannual clocks are synchronized with the environment by changes in photoperiod, light intensity and possibly temperature and seasonal rainfall patterns. Annual timing mechanisms are presumed to have important ultimate functions in seasonally regulating reproduction, moult, hibernation, migration, body weight and fat deposition/stores. Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons (e.g. equatorial residents, migrants to equatorial/tropical latitudes) rely more on their endogenous clocks than birds living in environments that show a tight correlation between photoperiod and seasonal events. Such population-specific/interspecific variation in reliance on endogenous clocks may indicate that annual timing mechanisms are adaptive. However, despite the apparent adaptive importance of circannual clocks, (i) what specific adaptive value they have in the wild and (ii) how they function are still largely untested. Whereas circadian clocks are hypothesized to be generated by molecular feedback loops, it has been suggested that circannual clocks are either based upon (i) a de-multiplication ('counting') of circadian days, (ii) a sequence of interdependent physiological states, or (iii) one or more endogenous oscillators, similar to circadian rhythms. We tested the de-multiplication of days (i) versus endogenous regulation hypotheses (ii) and (iii) in captive male and female house sparrows (Passer domesticus). We assessed the period of reproductive (testicular and follicular) cycles in four groups of birds kept either under photoperiods of LD 12 L : 12 D (period length: 24 h), 13.5 L : 13.5 D (27 h), 10.5 L : 10.5 D (23 h) or 12 D : 8 L : 3 D : 1 L (24-h skeleton photoperiod), respectively, for 15 months. Contrary to predictions from the de-multiplication hypothesis, individuals experiencing 27-h days did not differ (i.e. did not have longer) annual reproductive rhythms than individuals from the 21-or 24-h day groups. However, in line with predictions from endogenous regulation, birds in the skeleton group had significantly longer circannual period lengths than all other groups. Birds exposed to skeleton photoperiods experienced fewer light hours per year than all other groups (3285 versus 4380) and had a lower daily energy expenditure, as tested during one point of the annual cycle using respirometry. Although our results are tantalizing, they are still preliminary as birds were only studied over a period of 15 months. Nevertheless, the present data fail to support a 'counting of circadian days' and instead support hypotheses proposing whole-organism processes as the mechanistic basis for circannual rhythms. We propose a novel energy turnover hypothesis which predicts a dependence of the speed of the circannual clock on the overall energy expenditure of an organism.

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Section: (D) Proximate Mechanisms Underlying Circannual Rhythmsmentioning

confidence: 96%

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Wikelski

Martin

Scheuerlein

et al. 2007

Phil. Trans. R. Soc. B

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“…In fact, antelope ground squirrels initiate their breeding season in late winter in order to produce young by early spring, before the onset of summer drought (Kenagy and Bartholomew, 1985). Although many laboratory studies have been conducted on A. leucurus (DeCoursey, 1973;Kenagy, 1978Kenagy, , 1981Kenagy and Bartholomew, 1979;Kenagy and Vlek, 1982;Pengelley, 1966;Pengelley et al, 1976;Pohl, 1983Pohl, , 1998, no previous study has investigated the circadian rhythmicity of its body temperature. In the present study, we found that under conditions approximating thermoneutrality in the laboratory, antelope ground squirrels exhibited a robust daily rhythm of body temperature that was as stable as that of non-hibernating rodents but had mean and amplitude similar to that of hibernators during the euthermic stage of the annual cycle.…”

Section: Discussionmentioning

confidence: 99%

Circadian rhythms of body temperature and locomotor activity in the antelope ground squirrel, Ammospermophilus leucurus

Refinetti

Kenagy

2018

Journal of Thermal Biology

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We studied circadian rhythms of body temperature and locomotor activity in antelope ground squirrels (Ammospermophilus leucurus) under laboratory conditions of a 12L:12D light-dark cycle and in constant darkness. Antelope ground squirrels are diurnally active and, exceptionally among ground squirrels and other closely related members of the squirrel family in general, they do not hibernate. Daily oscillations in body temperature consisted of a rise in temperature during the daytime activity phase of the circadian cycle and a decrease in temperature during the nighttime rest phase. The body temperature rhythms were robust (71% of maximal strength) with a daily range of oscillation of 4.6°C, a daytime mean of 38.7°C, and a nighttime mean of 34.1°C (24-h overall mean 36.4°C). The body temperature rhythm persisted in continuous darkness with a free-running period of 24.2h. This pattern is similar to that of hibernating species of ground squirrels but with a wave form more similar to that of non-hibernating rodents. Daily oscillations in body temperature were correlated with individual bouts of activity, but daytime temperatures were higher than nighttime temperatures even when comparing short episodes of nocturnal activity that were as intense as diurnal activity. This suggests that although muscular thermogenesis associated with locomotor activity can modify the level of body temperature, the circadian rhythm of body temperature is not simply a consequence of the circadian rhythm of activity.

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Endogenous annual rhythm of reproductive function in the non-hibernating desert ground squirrelAmmospermophihis leucurus

Kenagy

1981

J. Comp. Physiol.

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Circannual rhythmicity in a non-hibernating ground squirrel, Citellus leucurus

Cited by 9 publications

References 19 publications

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Avian circannual clocks: adaptive significance and possible involvement of energy turnover in their proximate control

Circadian rhythms of body temperature and locomotor activity in the antelope ground squirrel, Ammospermophilus leucurus

Endogenous annual rhythm of reproductive function in the non-hibernating desert ground squirrelAmmospermophihis leucurus

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