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Information on the widespread function of the suprachiasmatic (SCN) pacemaker has increased dramatically in the past decade for laboratory rodents and for humans. Interest is now also growing in the adaptive value of SCN pacemakers in wild species of free-living mammals in natural pristine habitat. The squirrel family, Sciuridae, is highly diverse in North America. Radiation into many specialized groups has evolved in response to the temporal and spatial characteristics of specific habitats. The sciurids thus offer possibilities for comparison of SCN function for closely related species from very different habitats. Results from field and laboratory investigations concerning the ecological significance of the SCN are reported here for three ground squirrel species. The semi-fossorial antelope squirrels of the American southwest deserts were arrhythmic in above ground activities after deletion of the SCN pacemaker. In a desert enclosure, predation rates rose dramatically for lesioned animals in comparison ...

Laboratory and field data relevant to the survival value of the suprachiasmatic nuclei (SCN) pacemaker are presented for 4 related North American squirrel species that evolved in habitats with markedly different environmental conditions. Laboratory studies used free-running activity rhythms under constant conditions as the signature of an endogenous pacemaker. Field studies documented the circadian ecology of the 4 species; survival of intact controls was compared, when possible, with an SCN-lesioned group of free-living animals or with wild-caught animals in a laboratory facility that simulated natural conditions. All 4 species were rhythmic in the laboratory as indicated by precise free-running wheel-turning rhythms under constant conditions, as well as by photo-entrainment of free-runs to a 24-hr light-dark schedule. Southern flying squirrels (Glaucomys volans) presumably minimized predation by sleeping in sheltering tree dens during daylight, with awakening by their SCN timer for nocturnal gliding. Eastern chipmunks (Tamias striatus) were strictly diurnal but avoided predation in elaborate dens as well as by facultative hibernation and winter food caches. Antelope squirrels (Ammospermophilus leucurus) were also diurnal with dens for minimizing predation at night. Golden-mantled ground squirrels (Spermophilus lateralis) were diurnal, fossorial species with protective dens; during the extended hibernation in winter, the SCN played a role in limiting the time spent in arousal episodes. Thus, in the evolution of the physiology and behavior of these species, the SCN has become involved in diverse functions ranging from regulation of activity to reduction of energy expenditure during arousal episodes of hibernating ground squirrels.

The importance of circadian timing was evaluated for 18 months from late-April 1997 through October 1998 in a high-density population of free-living eastern chipmunks, Tamias striatus, at a 4-ha forest site in the Allegheny Mountains. Included in the radio-collared field group were 30 chipmunks with supra-chiasmatic nucleus-targeted lesions, 24 surgical controls, and 20 intact controls. An additional 17 chipmunks were used in a laboratory study as lesion-calibration controls to correlate degree of circadian arrhythmicity with extent of supra-chiasmatic nucleus deletion. Survival was documented in the field by daily radio tracking and by regular trapping censuses except during winter hibernation. A significantly higher proportion of supra-chiasmatic nucleus-lesioned than surgical control chipmunks or intact controls were killed by weasel predation during the first 80 days after repatriation. A 28-h continuous census found no surface activity of any chipmunks during hours of darkness. However, episodes of nocturnal movement were detected within the permanent dens by radio telemetric data logging, especially in supra-chiasmatic nucleus-lesioned animals. Excavation and mapping of six chipmunk burrow systems aided in the interpretation of the telemetric activity data. Nighttime restlessness of supra-chiasmatic nucleus-lesioned animals may have acted as a clue to the predator for locating its prey.

We isolated and characterized 16 microsatellite loci in the eastern chipmunk, Tamias striatus. The loci were screened across 25 individuals from one population and shown to be polymorphic with the number of alleles per locus ranging from two to 17. Polymorphic information content ranged from 0.212 to 0.887 and observed heterozygosity ranged from 0.200 to 0.960. Only two loci (Chip 10 and Chip 25) deviated from Hardy–Weinberg equilibrium.

Circadian activity parameters of 53 white-tailed antelope ground squirrels, Ammospermophilus leucurus, were measured to determine the role of the suprachiasmatic nuclei (SCN) pacemaker in their health and survival. Wheel-running activity was monitored in the laboratory with 44 individuals to document the presence of free-running circadian rhythms and ability to entrain to light-dark cycles. Twenty-two individuals were returned to the desert site of origin, including 12 intact control animals and 10 animals whose circadian timing had been disrupted by SCN-lesioning. Time of activity was recorded continuously for 15 days in a large outdoor enclosure by a motion detector, a microchip transponder detector, and video surveillance. An unplanned nighttime attack by a feral cat resulted in the death of 60% of the SCN-lesioned animals and 29% of the control animals in the enclosure. Surface activity of SCN-lesioned animals at the food cache occurred both in daytime and at night, ranging from 16.0% nighttime activity for one partially lesioned individual to 52.1% for one completely lesioned animal. Controls were strongly day-active, with nighttime surface trips constituting only 0-1.3% of all excursions to the cache. Nine wild free-ranging individuals, including one with a radiotransmitter collar, were exclusively day-active. One of the functions of the SCN in mammals may be to reduce activity of animals during times that are unfavorable for activity.

The amount of daily light exposure was measured for a nocturnal rodent, the flying squirrel, Glaucomys volans , in an artificial den. The role of this light exposure in circadian photo-entrainment was assessed by means of telemetric monitoring of multiple activity functions of individual animals. Novel simulated den cages facilitated temporal and sparial tracking of each animal from its darkened nestbox through a darkened passageway to an activity chamber. The time exposed to light ranged for six individual flying squirrels during an entrainment schedule from 0·4–3·5% of the light period. The data suggest that this den-dwelling, nocturnal rodent, with free-running rhythms of slightly less than 24 h in period, synchronized its active time with the hours of darkness by viewing brief amounts of the daily light cycle at dusk when circadian arousal occurred.

The necessity of a circadian pacemaker, the suprachiasmatic nuclei (SCN), for survival was evaluated in a population of approximately 65 wild eastern chipmunks, Tamias striatus. The research involved over 3000 h of fieldwork between May 1995 and October 1997 on a study siteat Mountain Lake Biological Station, Virginia. The 28 chipmunks randomly designated as project animals included 10 SCN-lesioned chipmunks, 5 surgical controls (shamlesioned), and 13 intact controls. Visual observation, live trapping, and radio telemetric tracking were used to assess 6aspects of survival and reproduction. Upon release after surgery, every animal returned to its den site and was able to maintain its home territory. In warm months from May through October, all chipmunks were active above ground with a strictly day-active pattern. During the remainingcold months, they were normothermic but relatively torpid in their underground densfor extendedperiods of time. Short-term mortality for the initial 3 months included only a single intact control chipmunk; loss for the extended period from August 1995 to October 1996 was 40% for the SCN-lesioned animals, 0% for surgical controls, and 15.4% for the intact controls.Survival differences were not significant between surgical control and intact control groups but were significant ([.alpha] = .10) between SCN-lesioned and pooled control groups. Annual bodyweight patterns were similar for both groups. Most individuals in both SCN-lesioned and controlgroups were reproductively active in the spring and fall breeding periods. Lack of major differences may be attributable to the exceptionally favorable conditions for survival such as a veryabundant fallacorn crop, medium population size, and absence of heavy predation.

Modulation of the free-running circadian period of wheel-running activity by prior entrainment was studied in flying squirrels by two different methods. First, animals in standard bin cages were entrained to two consecutive photoentrainment light-dark schedules (12L: 12D) separated by a period of darkness (DD). The mean free-running period for 10 squirrels in constant darkness lengthened from 23.75 h initially to 23.86 h following the first entrainment and 23.90 h after the second entrainment. The mean period reverted during the final 8 wk of constant darkness to 23.86 h. Because of inherent limitations of standard bin cages, a second approach utilized simulated den cages. Assessment of photic information by squirrels for photoentrainment to an LD schedule occurred in den cages chiefly during a few minutes at the time of arousal from the rest period (CT 12). A phase delay in onset of activity occurred, accompanied by a long-lasting lengthening of the apparently free-running pacemaker. Frequency modulation...

The effect of water samples from three dredging locations in Charleston Harbor and its tributaries upon the physiology of larval or juvenile zooplankton was determined, Daphnia were used for Location 1 with a salinity of 0‰, Paleomonetes for Location II with intermediate salinities and Polydora for Location III with highest salinities. Water from the disposal area of each location was most toxic. Samples from 200 yd downstream were intermediate in effect, and the dredge site sample was least toxic.

Although birds are a conspicuous element in estuarine ecosystems, annual fluctuations in the size and structure of avian salt marsh communities have not been studied extensively. From October 1978 through October 1980, we censused an avian community inhabiting a 3000-hectare estuary in SC using 4 censusing techniques: bi-monthly aerial surveys, airboat surveys, ground counts at communal roosts, and almost daily spot checks through the marsh for transient species. Avian density averaged 2.6 birds/hectare and avian biomass averaged .7 Kg/hectare annually. Ninety-five species of birds from 12 avian orders fed on the marsh during the 2-year period. Over one-third of the species were members of the order Charadriiformes. Species counts were greatest in spring and fall during migration and lowest in winter and summer. Similar peaks and troughs occurred in biomass and in number of birds sighted. Migrating passerines, mostly swallows, comprised a significant portion of the population in early fall and wading birds comprised a significant portion of the avian biomass in the early part of the breeding season as well as during the late summer when large number of White Ibis fed on the marsh. Clapper Rails and shorebirds, especially dowitchers, dominated the avian community throughout most of the year.

Neural transplants into the third ventricle utilized to quantitatively assess the effectiveness of fetal tissue from selected brain sites in restoring circadian locomotor rhythmicity of adult hamsters rendered arrhythmic by lesions of the suprachiasmatic nuclei (SCN). Circadian function was continuously monitored in recording wheel cages under controlled environmental conditions. Animals which remained arrhythmic for 3-4 weeks after SCN lesions received transplants of neural tissue from 13-14-day-old fetuses: either SCN tissue or non-SCN tissue (cerebral cortex or hypothalamus excluding SCN). Quantitative evaluation of the data indicated partial restoration of circadian rhythmicity in 37% of 19 animals with SCN transplants, but in 0% of the 9 animals with non-SCN neural transplants. The mean time for reappearance of rhythmicity was 20 days after SCN transplantation. Animals were sacrificed 8-10 weeks after transplantation for histological analysis in order to visualize lesion placement and to characterize transplants. The cytoarchitecture and neuropeptide organization of the transplants were consistent with the brain region. Only SCN transplants were characterized by aggregates of small neurons with codistributed immunoreactivity for SCN-characteristic neuropeptides.

1. Am nachtaktiven Flughornchen, Glaucomys volans, wurden endogene und exogene Faktoren untersucht, die die tagliche Aktivitat bestimmen. Der Beginn der Aktivitat in Lauftrommeln an aufeinanderfolgenden Tagen lieferte das Kriterium, mit dessen Hilfe die Eigenschaften der endogenen Aktivitatsperiodik und quantitative Wirkungen des Lichtes auf die Periodik am besten erfast werden konnten. 2. In ununterbrochener Dunkelheit dauerte die Aktivitatsperiodik eines Flughornchens uber langere Zeitspannen mit gleichbleibender Frequenz an. Unterschiedliche Periodendauern gleichzeitig gemessener Flughornchen und Phasenverschiebungen gegenuber der Ortszeit sprachen fur die endogene Natur dieser Periodizitaten. Die Perioden hatten eine Dauer von 23–24 1/2 Std; der kleinste mittlere Fehler des Einzelwertes betrug ±2 min (gemessen uber 15 Tage). Weder periodische noch aperiodische Gerausche beeinflusten die Aktivitatsperiodik der Hornchen. 3. Dauernde Belichtung verlangerte die Periode. 4. Kunstlicher oder naturlicher Licht-Dunkel-Wechsel synchronisierte die Flughornchen derart, das jeweils die Aktivitatszeit in die Dunkelzeit fiel. Offensichtlich waren hierfur Phasenverschiebungen verantwortlich, die auftraten, wenn Licht auf bestimmte Teile der Periode fiel. 5. Flughornchen im Dauerdunkel wurden in Abstanden von mehreren Tagen jeweils 10 min lang mit etwa 5 Lux belichtet. Derartige “Licht-Blitze“ bewirkten Phasenverschiebungen, deren Grose sich nach der getroffenen Phase richtete. Es ergab sich eine periodisch wechselnde Licht-Reaktion: Maximal verzogernde Phasenverschiebungen bei Beginn der Aktivitat; anschliesend 6–7 Std geringer werdende Phasenverschiebungen und schlieslich eine kurze Zeitspanne, in der Beschleunigungen auftraten. Wahrend der restlichen Stunden einer Periode, bis etwa 1 Std vor Aktivitatsbeginn, blieb der Licht-Blitz wirkungslos. 6. Ein ahnlicher Mechanismus fur die Steuerung der Aktivitatsperiodik mag bei dunkelaktiven Nagetieren weit verbreitet sein.

Bats living under laboratory or field conditions manifested precise nocturnal activity rhythms. Light-sampling at the light-to-dark transition was apparently the chief means of synchronizing an endogenous, non-24-hour activity rhythm to the daily light cycle.1. Two horseshoe bats, free-living in separate, small recording rooms, readily adjusted the time of activity to correspond to an L:D schedule.2. Three horseshoe bats, roosting in a darkened tunnel with no direct view of the 12L:12D schedule of the outside room, anticipated the light-dark change by flying out regularly during the hour before the lights were turned out, then were active for about 8 hours.3. A colony of Myotis myotis exited from a church loft at an average light intensity of 0.05 lux and returned at dawn. Attempted darkening of the church did not result in earlier light-sampling. Illumination of the flight path at the normal exit time resulted in intense sampling but prevented the actual departure of most of the bats.

Activity rhythms of 3 species of day‐active sciurid rodents under various constant lighting conditions and in L/D schedules were studied. The animals included 8 white‐tailed antelope squirrel Ammospermophilus leucurus, 5 black‐tailed antelope squirrel A. harrisi, and 5 eastern chipmunk Tamias striatus. All species showed free‐running rhythms in constant conditions, with the period decreasing at higher intensities. The 3 species synchronized readily to a variety of light schedules, with the exact response dependent upon the phase relationship of activity to the new light schedule.

The activity rhythms of 5 flying squirrels,Glaucomys volans, and 7 chipmunks,Tamias striatus, were examined under controlled conditions in the laboratory. Free-running, circadian rhythms were demonstrated using a total of 25 LL or DD experiments. With 46 LD schedules the limits of entrainment in a 24-hour day were determined, and the phase angle difference for each schedule measured.Glaucomys was able to synchronize to schedules ranging from 1 second of light per 24-hour day to at least 18 hours light per day with little or no change in the phase angle.Tamias showed an oscillatory type of entrainment when the photoperiod was less than 3 hours per 24-hour day or greater than 23 hours, but in the intervening region was capable of stable entrainment. A tendency was evident for the phase angle difference to become less positive as the LD ratio increased. InGlaucomys single, isolated light pulses of either one second or 24 hours duration were able to bring about relatively large shifts in the phase of the activity rhythm.

Experiments were carried out using simulated den cages to delineate specific char acteristics of phase delaying in circadian photoentrainment of a nocturnal rodent, the flying squirrel. The principal experiments entailed presentation of one to five consecutive 15-min white-light pulses per activity cycle at activity onset to animals free-running in darkness, in order to determine the immediate and final phase-shifting effect. Auxiliary experiments recorded entrainment patterns on light-dark (LD) schedules in the den cages. Phase response curves (PRCs) based on 15-min white-light pulses in standard wheel cages were also constructed for these animals as background information for interpreting the phase-delaying experiments. Exposure of a den animal to light by light sampling at the time of initial arousal from the rest state at circadian time (CT) 12, either by an LD schedule or by a 15-min light pulse, resulted in a return to the nest box for a short rest period. The phase delay occurring after a single light exposure at activity onset was equal to the induced rest, thus suggesting an immediate phase shift. The maximum delay was about 11/2 hr/cycle, with the amount of delay related to the number of light exposures. During the photoentrained state on an LD schedule, the activity rhythm of a den-housed animal was essentially free-running on the days following a phase delay. The data are used to expand current models for photoentrainment of circadian activity rhythms in nocturnal rodents.

Environmental light cycles are the dominant synchronizers of circadian rhythms in the field, and artificial light cycles and pulses are the major tools used in the laboratory to analyse properties of circadian systems1–4. It is therefore surprising that few studies have analysed the physical parameters of light stimuli that affect circadian rhythms. There have previously been no spectral sensitivity measurements for phase shifting the circadian rhythms of mammals and only two preliminary reports on the wavelength dependence of this response exist3,4. Using the magnitude of phase shift caused by a single 15-min pulse of monochromatic light given 6 h after activity onset, we have now characterized the spectral sensitivity of the photoreceptors responsible for phase shifting the locomotor rhythm of the hamster (Mesocricetus auratus). The sensitivity curve for this response has a maximum near 500 nm and is similar to the absorption spectrum for rhodopsin. Although the spectral sensitivity is consistent with a rhodopsin-based photopigment, two features of the photoreceptive system that mediates entrainment are unusual: the threshold of the response is high, especially for a predominantly rod retina like that of the hamster, and the reciprocal relationship between intensity and duration holds for extremely long durations (up to 45 min). These results suggest that the photoreceptive system mediating entrainment is markedly different from that involved in visual image formation.

Behavioral aspects of photoentrainment of circadian locomotor activity rhythms were recorded for a nocturnal den-dwelling rodent, the flying squirrel, Glaucomys volans. Methods included both telemetric monitoring and infrared observations of animals under constant dark (DD) or light-dark (LD) schedules in either standard wheel cages or in newly developed simulated den cages. By means of the den cages, several aspects of a circadian activity cycle could be simultaneously measured emphasizing the arousal from rest, the light-sampling behavior by which a squirrel assessed the environmental photoregimen, and the phase-shifting by which photoentrainment was achieved. Each animal in a den cage remained for 12 or more hours of its rest period almost exclusively in the darkened nest box, then at an abrupt arousal time moved to the light-sampling porthole. In darkness each animal initiated wheel activity immediately after arousal; light at arousal time, however, induced a return to the nest box for a nap and a delay phase-shift in onset of activity of approximately 40 min. On subsequent days, each animal appeared to be free-running (tau FR less than 24 h) until onset again advanced into the light period. A squirrel usually viewed only a few minutes light per day, and on free-running days occasionally saw none of the 12-h light period. The significance of these data for theories of circadian photoentrainment is discussed.

A battery of tests was used to determine the effects of three dilute mercuric chloride solutions on larval stages (Zoea I, III, V) of the fiddler crab Uca pugilator (Bosc). The influence of both acute and chronic exposures on viability, oxygen consumption, and swimming activity was measured. No stage V and only a few stage I or III larvae were able to survive a concentration of 9 * 10-7 M HgCl2 (0.18 ppm Hg) longer than 24 hr; an exposure as short as 6 hr resulted in reduced metabolism and swimming rate of all stages. Although concentrations of 9 * 10-9 M HgCl2 (0.0018 ppm) and 9 10-11 M HgCl2 (0.000018 ppm) were sublethal, 24-hr exposures did affect metabolism and swimming. Some larvae reared in the more dilute mercury solutions developed to the megalopa stage, but survival was reduced in relation to the mercury concentration. The data from all tests suggest that toxicity of mercury increases with larval age.