Evidence for existence of a yearly clock in surgically and self-blinded chipmunks.

Abstract

By use of simplified technique and constant environmental conditions, I have demonstrated the existence in the chipmunk of a yearly clock. In a blinded chipmunk the clock manifested itself by remarkably consistent changes in running activity, food and water intake, and body weight over 61/2 yr. Studies on freshly trapped chipmunks kept in the same laboratory environment but with alternating light and darkness (12 hr each), showed that, when their eyes were covered for much of the light period, they reduced their exposure to light to preserve the activity of the yearly clock. Laboratory-adapted chipmunks that do not shield their eyes from light do not show the clock. The yearly clock has all the characteristics of the 24-hr clock, including sharply defined active and inactive phases, and must likewise play an important part in the animal's survival. Light would appear to be the chief or only cue for the clock. The period lengths did not change with age during the 61'2 yr.Men have long talked of yearly cycles but never has there been a clear demonstration under experimentally controlled conditions of a yearly clock that actually measures phases of activity followed by phases of total inactivity. This paper presents evidence supporting the existence of such a yearly clock-not simply of a yearly cycle or rhythm-and the importance of the role played by light in control of this clock.Pengelley and Fisher (1) found a yearly cycle in food intake and body weight in golden-mantled ground squirrels kept in alternating 12 hr of light and darkness and at external temperatures of 22°and 00. One animal at 220 showed two cycles and the other, at 00, showed 21/2 cycles. Manifestation of the cycle in the presence of the alternating light and darkness indicated to them that light could not be an all-important cue or Zeitgeber. In fact, Pengelley and Asmundson (2) stated that "ambient temperature, light, access to motor activity, and opportunity to breed are all potential Zeitgebers." After reviewing results of the search by Pengelley and Fisher and by a number of other workers for a Zeitgeber, Mrosovsky (3) concluded that "If there is one, it certainly does not seem likely to involve light."Most students of hibernation and heat conservation, particularly Pengelley and Fisher, Heller and Poulson (4), and Drescher (5), have made a point of always supplying their animals with "ample" nest-building material or closed boxes or nesting chambers. In this way the animals could cover or shield their entire bodies including their eyes, thus perhaps allowing them to functionally "blind" themselves. This could mean that in many instances in which animals seemed to be exposed to light they could have been "self-blinded." The present paper will bring out the importance of blinding that could have occurred in this way.Because studies on the 24-hr clock in mice, rats, hamsters, and squirrel monkeys established that blinding or constant darkness was necessary to free the 24-hr clock from its normal entrainment to light (6-), the present e...

Late summer activity changes in populations of Eastern Chipmunks (Tamias striatus)

“…Captive chipmunks exposed to natural envir-Onmental temperatures entered torpor in winter and Spring but did not estivate in summer (Wang and Hudson 1971). Richter (1978) presented data supporting the contention that the activity-inactivity phases of the Eastern Chipmunk are controlled by a yearly clock which is set by, but not dependent on, photoperiod. The winter inactivity phase is clearly shown by his data, but no other inactivity period is evident.…”

Persistence of circannual rhythms under constant periodic and aperiodic light conditions: sex differences and relationship with the external environment

“…Circannual rhythms have been found to persist for several cycles in both birds and mammals, suggesting that a circannual clock can function throughout the life of an individual (Pengelley and Asmundson, 1969;Pengelley and Asmundson, 1974;Richter, 1978;Gwinner, 1986). The most compelling evidence for circannual rhythms comes from experiments in which captive birds kept on constant and 'neutral' photoperiods (e.g.…”

Effect of photoperiod on fat accumulation in juvenile Citellus lateralis born in captivity

“…photoperiod and weight cycles have been plagued ~~~k (1955) noted that body weights in C. un-by two uncertainties: (1) wild-caught animals may dulatus increased as photoperiod decreased and have been entrained to the natural photoperiod suggested that short days might act as a stimulus for prior to their exposure to artificial ~h o t o~e~~o~~ hibernation. Richter (1978) and Brenner and Lyle and (2) weight changes may be caused by shifts in water content in the gut and (or) accumulation of 'Present address: Department of Zoology and Entomology, body fat. It was, therefore, our purpose to deter- cumulation of body fat in C .…”