Circadian locomotor activity in the Virginia opossum

Abstract

The locomotor activity of two Virginia opossums was measured underD 24 and LD 12:12 conditions. Ss were inactive during the day and displayed two peaks of activity at night. The length of the activity period was approximately 24 h. Under LD 12:12 the nocturnal cycle was more pronounced than under D 24. The period length and topography of the . opossum's locomotor activity cycle are comparable to those obtained from other nocturnal mammals under similar lighting conditions. Cone & Cone (1968) demonstrated that Virginia opossums were more active between 10:00 p.m. and midnight than between 10:00 a.m. and noon. In addition, nighttime activity was significantly higher in the dark and under ambient illumination levels of 1 and 2~ fc than it was under illumination levels of 5,25, aq.d 50 fc. These two observations indicate that the opossum is nocturnal. The purpose of the present study was to describe the topography of the opossum's locomotor activity pattern and specify its period length under conditions of constant darkness (D 24) and alternating light and darkness (LD 12:12) METHOD Subjects Two opossums, one male and one female, served as Ss. They weighed about 750 g and were 3 months out of the pouch at the beginning of the study. Both had been gentled. Prior to the beginning of the experiment, the Ss had lived in individual cages in a colony room automatically maintained on LD 12: 12. Throughout the experiment, they were maintained on an ad lib diet of Purina dog chow, meat, fruit, and water. Apparatus Each S lived in a 61 x 43 x 43 em wooden tilt box. A microswitch was mounted at each end of the tilt box, and electronic equipment was programmed so that depression of either microswitch yielded one count. These counts were automatically recorded hourly on electromechanical counters and on a BRS Foringer printout counter. The tilt boxes were placed on a sturdy platform and separated from each other by a partition. A food well was mounted inside each box at the central pivot point on one side. A water-bottle spout protruded through a small hole directly opposite the foodwell. The parallel metal bars of the box floor allowed fecal material to fall into sawdust-filled pans. The ambient temperature of the test chamber remained stable at 73°F ± 3 0 throughout the experiment. Continuous white noise of approximately 85 dB was presented by a small speaker mounted above each tilt box. Procedure A t varying times on every third day, E entered the test room, added food and water, and changed the waste pans. During dark conditions, E turned off all lights in the area of the test chamber *Thanks to Sidney L. Sanders and Lila Goodson for help in collecting and analyzing the data.

Some variables affecting feeding cycles in the opossum

“…A number of investigators have studied the effects of the light-dark (LD) cycle upon activity (Ashby, 1972;D. M. Cone, 1973 Cone, 1968) and upon feeding and drinking behavior (Rusak & Zucker, 1974;Stephan, 1984).…”