Uinta ground squirrels (Spermophilus armatus) were instrumented with ECG radio-transmitters. Heart rate and oxygen consumption were monitored for one hour at ambient temperatures above, within and below the thermoneutral zone. These measures were made at predetermined intervals throughout the active season of squirrels to determine if the heart rate-oxygen consumption relationship was a stable linear regression within and between squirrels during this period. Heart rate and oxygen consumption were also monitored for squirrels exposed to artificial and natural stressors. These squirrels were then released in an outdoor enclosure. Heart rate and behavior of animals were monitored simultaneously during above and below ground activity. Heart rate-oxygen consumption regressions were stable during measurements through a 25°C temperature range. Regressions of heart rate versus oxygen consumption did vary between and within squirrels over four days. Heart rate tended to decrease initially after presentation of natural stressors. Heart rate tended to increase when artificial stressors were presented. Regressions of heart rate versus oxygen consumption for these stressors tended to be linear, but heart rate would not be a good predictor of oxygen consumption during rapid heart rate changes because, in most cases, heart rate-oxygen consumption regressions were not statistically significant. In some tests with rapidly decreasing initial heart rates, the heart rate-oxygen consumption relationship was negative. that is, oxygen consumption remained constant as heart rate decreased. Possible causes of negative responses are discussed. Heart rate responses generated in laboratory stress tests were similar to semi free-living heart rate responses. During the major portion of time spent above and below ground, heart rate of squirrels was found to be quite stable. During these periods, heart rate should be a reasonable predictor of oxygen consumption. In summary, average heart rate should be a reasonable predictor of oxygen consumption of free-living squirrels over daily periods. In using this method, it would be necessary to calculate regressions of heart rate and oxygen consumption in the laboratory before and after free-living studies to examine the stability of the regression lines during this period. An average regression line could be used to compensate in part for a change of the heart rate-oxygen consumption relationship during study periods.

Various methods were employed to detect changes in the peripheral degradation of thyroxine (T4) in adult Uinta ground squirrels (Citellus armatus) collected at two different altitudes (5400 and 9000 feet.) Plasma half-life of injected T4-125I (tl/2) was significantly decreased with altitude, as was T4-125I distribution space (TDS) and T4 degradation and secretion rate (TSR). In vitro deiodination of T4-125I by heart homogenates was not affected, while urinary excretion of thyroxine derived iodide was increased at high altitude 44-70 hours post-injection. Both total and free serum T4 concentrations were reduced at high altitude, although not significantly. The cause of the reduced tl/2 at high altitude was not evident, while the decreased TDS was probably due to a reduced plasma volume. Increased urinary and fecal clearance could account for the decreased total and free serum T4. TSR was reduced due to the low TDS and T4 concentration observed in high altitude squirrels.

Thyroid uptake and distribution of 125I, concentrations of T4 and T3 in serum and thyroids and concentrations of TSH in serum and pituitaries were measured to determine thyroid function of Uinta Ground Squirrels (Citellus armatus) native to 5,400 and 9,000 feet elevations to evaluate alterations in the state of the thyroid due to increased altitude. Uptake of 125I was 60 percent lower by squirrels from 9,000 feet. Incorporation of 125I into T3 was greater at the higher elevation, but absolute thyroid T3 concentrations were similar at both elevations. No significant differences were found in serum T3 concentrations, but squirrels living at 9,000 feet had higher serum T4 levels than those living at a lower elevation. Urinary excretion of T3 by squirrels from the 9,000 feet elevation was lower compared to excretion by squirrels native to 5,400 feet. Elevated pituitary TSH levels were also found in squirrels native to the higher altitude. These findings indicate a chronic hypothyroid state of squirrels living at 9,000 feet compared to those living at 5,400 feet.

No description available.

Previous research on the relationship between spatial memory and adult hippocampal neurogenesis has been controversial. In the present study, neurogenesis was compared between two natural populations of the same species that differ in their reliance on spatial memory to cache and retrieve stored food. Western red squirrels store food in a single site whereas eastern red squirrels store food in multiple sites. Neurogenesis was assessed using endogenous markers of the number of proliferating cells (Ki-67) and the number of immature neurons (DCX), and neuronal recruitment was determined by measuring the area of the dentate gyrus of the hippocampus. The number of proliferating cells, immature neurons and neuronal recruitment were enhanced in the eastern compared to the western red squirrels, reflecting the food storing strategies used by the squirrels. This suggests that there is a positive correlation between adult hippocampal neurogenesis and spatial learning and memory.

Previous research on the relationship between spatial memory and adult hippocampal neurogenesis has been controversial. In the present study, neurogenesis was compared between two natural populations of the same species that differ in their reliance on spatial memory to cache and retrieve stored food. Western red squirrels store food in a single site whereas eastern red squirrels store food in multiple sites. Neurogenesis was assessed using endogenous markers of the number of proliferating cells (Ki-67) and the number of immature neurons (DCX), and neuronal recruitment was determined by measuring the area of the dentate gyrus of the hippocampus. The number of proliferating cells, immature neurons and neuronal recruitment were enhanced in the eastern compared to the western red squirrels, reflecting the food storing strategies used by the squirrels. This suggests that there is a positive correlation between adult hippocampal neurogenesis and spatial learning and memory.

A trait must genetically correlate with fitness in order to evolve, however, theory suggests that strong directional selection should erode additive genetic variance (Va) in fitness and limit future evolutionary potential. Sexual antagonism and temporal fluctuations in selection are mechanisms that could maintain Va in fitness. Maternal genetic effects could be an additional source of adaptive genetic variation. I used ‘animal models’ to examine a long-term population of red squirrels to determine 1) if either sexual antagonism or temporal fluctuations in selection were maintaining direct Va in fitness or 2) if maternal genetic effects were a source of indirect Va in fitness. While there were environmental trade-offs on juvenile survival, neither sexual antagonism nor temporal fluctuations in selection maintained Va in fitness. Maternal genetic effects on fitness were significant and provide the Va in fitness needed for rapid microevolution. This is the first instance of maternal genetic effects demonstrated as the only genetic variance available for microevolution. / Northern Scientific Training Program, the Arctic Institute of North America, American Society of Mammologists, Queen Elizabeth II Graduate Scholarship in Science and Technology, NSERC Discovery (to Andrew McAdam), NSF (to Andrew McAdam)