ABSTRACT
Effects of hibernation on memory were tested in European ground squirrels (Spermophilus citellus). The animals were trained in summer to successfully accomplish two tasks: a spatial memory task in a maze and an operant task on a feeding machine. One group hibernated normally, and the other was prevented from hibernation by maintaining ambient temperature at 22 degrees C. In spring, the same tasks were repeated for both groups and their individual performances compared to the initial training phase. The experimental groups differed significantly in both tasks. The nonhibernating animals had higher levels of retention and needed significantly fewer trials to relearn the tasks than the group that had hibernated. In addition to testing the retention of conditioned tasks, social memory was also studied. The ground squirrels were given a social recognition test in spring with one familiar and one unfamiliar conspecific. In contrast to the conditioned tasks, social memory did not seem to be affected by hibernation. The results indicate negative effects of hibernation on the retention of conditioned tasks, which could produce important constraints on animals. A potential explanation for this memory loss might be changes in neuronal activity, which occur during hibernation.
Subject(s)
Hibernation/physiology , Memory/physiology , Animals , Interpersonal Relations , Male , Maze Learning/physiology , Motor Activity/physiology , Retention, Psychology/physiology , SciuridaeABSTRACT
The course of behavioral and vaginal estrus and patterns of circulating estrogens were followed in free-living European ground squirrels (Spermophilus citellus) after their emergence from hibernation. Normally mating females were compared to a second group in an area where males had been removed from the population before female emergence. Both groups showed vaginal estrus, but the patterns differed. Mating shortened vaginal estrus to a 3-day period compared to 8 days in unmated females. The extent (cell number) of cell cornification during estrus and the cellular components (percentage distribution) of metestrus did not differ between the two groups. Females in the area without males had significantly higher estrogen levels during estrus and metestrus compared to those in the control area. European ground squirrels were found to be monestrous, as none of the unmated females reentered estrus after metor diestrus was detected. The prolongation of vaginal estrus in unmated females can be viewed as either a physiological inevitability or an adaptation to low mate availability. The extension is still relatively short compared to other sciurid species and perhaps a product of constraints producing a strict time frame for reproduction.
Subject(s)
Copulation/physiology , Estradiol/blood , Estrus/physiology , Sciuridae/physiology , Animals , Animals, Wild , Diestrus/physiology , Female , Hibernation , Male , Metestrus/physiology , Ovulation/physiology , Proestrus/physiology , Seasons , Vagina/cytology , Vagina/physiologyABSTRACT
Changes in the plasma titers of follicle-stimulating hormone were investigated in a free-living population of barheaded geese over the whole year. Adult males had pronounced seasonal changes from prebreeding levels of approximately equal to 20 ng/ml to a peak in the breeding season of about 300 ng/ml. Changes in females were only slight. An increase from nondetectable, approximately equal to 20 ng/ml to a mean of 32.2 ng/ml before egg-laying was found. The data are discussed with regard to the literature on free-living species and the previously published data on LH and testosterone levels in the same birds.
Subject(s)
Follicle Stimulating Hormone/physiology , Geese/physiology , Animals , Breeding , Female , Follicle Stimulating Hormone/blood , Male , SeasonsABSTRACT
A number of behavioral and physiological parameters including the circulating levels of 7 hormones were investigated in a free ranging population of barheaded geese in Seewiesen, W. Germany. Behavioral data were collected on the entire flock from which seasonal changes in the frequencies were determined. In addition, data on the behavior of individuals were obtained to aid in the comparison of seasonal changes in behavior and hormones. The resulting curves were used to examine whether the annual changes in the frequencies of various behaviors were related to changes in circulating hormonal concentrations. Lastly, the physiological data were discussed with regard to reproductive biology in birds.
