Circadian rhythms of locomotor activity in captive birds and mammals: Their variations with season and latitude

Abstract

1. The seasonal variations in time of daily onset and end of locomotor activity are described for 3 species of mammals and 5 species of birds kept in captivity at the arctic circle and at lower latitude. These variations are most pronounced at high latitude. 2. The duration of daily activity plotted versus the photoperiod can be described as an S-curve in all species studied so far, both in nature and in captivity. In both male and female fringillid birds activity times were longer before the summer solstice (spring) than after the summer solstice at equal photoperiods. 3. The seasonal changes in activity time result from roughly mirror-image changes in the times of onset and end of activity relative to sunrise and sunset, cancelling out each other. Therefore the midpoint of activity stays relatively stable; remaining minor changes in the midpoint of activity do not produce a general seasonal pattern. 4. At high latitude, a large seasonal fluctuation in the day-to-day variability (or precision) of activity timing is detected. These patterns of precision of the rhythm cannot be attributed to a single Zeitgeber property without complex assumptions. Onset and ends of activity become more precise when occurring during the civil twilight, i.e. at times of day with most rapid changes in light intensity. This may reflect direct action of light on the rhythm rather than a property of the entrainment mechanism. 5. The data do not give compelling evidence for any formal model of the oscillations driving the activity rhythms. Predictions concerning the relation between phase and activity time derived from a single oscillator model are not matched by the data. On the other hand, the general seasonal patterns can be easily described in terms of a two-oscillator model. 6. Seasonal variations in duration of activity are larger in birds than in mammals. Day-to-day variations in timing are larger in mammals than in birds. The implications for photoperiodic time measurement are discussed.

Winter circadian activity pattern of free-ranging coypus in the Paraná River Delta, eastern Argentina

“…The similarity between the circadian rhythms observed in our study area and those obtained in captive and feral coypus in areas where the species was introduced, suggest that the nocturnal pattern observed reflects an endogenous activity pattern which has evolved in the nature range (Aschoff 1966, Daan and Aschoff 1975, Gosling 1979). …”

Development of the mouse circadian pacemaker: Independence from environmental cycles

“…Plasticity is usefully viewed not as an inconsequential property of the pacemaker, but rather as a funtional and adaptive feature of its design. The adaptive significance of pacemaker plasticity may be related to seasonal changes in day length and the maintenance of an adaptive phase relationship to the environment as such changes occur (Pittendrigh and Daan 1976c;Daan and Aschoff 1975). That the period of the pacemaker and the range of its plasticity are under complete genetic control is, if not expected, at least reasonable in view of the astronomical regularities to which these properties are adapted.…”

Tuning the phase of circadian entrainment

“…This implies that short days are considered as a weak zeitgeber, whereas 12 L : 12 D cycles are a strong zeitgeber. This assumption has been proposed earlier [19] and was recently explored theoretically in a study on circadian seasonality [41]. It seems reasonable to assume that longer photoperiods represent stronger zeitgebers, as N. crassa is sensitive to the total amount of the received light [42].…”

“…Those results suggest that in addition to the period mismatch t 2 T, the ratio between the zeitgeber strength and the amplitude of circadian oscillations affects the entrainment phase. Furthermore, the phase of entrainment can depend on seasons and latitudes [19] and on additional clock parameters such as relaxation times and inter-cellular coupling [20].…”