The present work was done to determine the effect of temperature of the half-saturation constant (ø) and the maximum transport rate (K) of the facilitated diffusion of glycerol across the erythrocyte membrane of Peromyscus californicus.

In 1938, Jacobs, et al. discussed differences in the permeability of the erythrocytes of rat and mouse to erythritol, mannitol, glycerol, and thiourea. Rat erythrocytes were more permeable to glycerol than to thiourea, whereas the reverse was true for mouse erythrocytes. Mouse erythrocytes also displayed a high degree of permeability to erythritol. However, this same substance penetrated rat cells much more slowly. Small but recognizable permeability differences were soo demonstrated among a number of species within a single genus. Levine (1943) investigated species differences in rates of osmotic hemolysis within the genus Peromyscus. The four species studied were: P. eremicus fraterculus, P. leucopus noveboracensis, P. gossypinus palmarius, and P. T. truei. Consistent differences in hemolysis times were demonstrated and it was possible to identify each species with certainty. Later experiments (LeFevre, 1948) suggested that glycerol and glucose did not enter the human red cell by simple diffusion, but rather that these penetrants were transported into the erythrocyte by an active metabolic system in which at least one essential link involved a sulfhydryl group Jacobs, et al. (1950) examined the inter-class erythrocyte permeabilities of mammals, birds, reptiles, amphibians, and fish to isosmotic solutions of urea, thiourea, glycerol, and ethylene glycol. Their results, which were generally consistent within a given class, indicated an unusually high permeability of glycerol and ethylene glycol in bird erythrocytes, and for urea in mammalian red cells. It was also found that the permeability of chicken red blood cells differed noticeably from the rather uniform pattern seen in the erythrocytes of such species as the pigeon, herring gull, English sparrow, pheasant, and turkey. In 1961, Hunter studied the effect of butanol on the permeability of human, rabbit, sheep, and chicken erythrocytes to glycerol, monoacetin, thiourea, and ammonium chloride. This work suggested that when the movement across the cell membrane depended on simple diffusion, butanol increased the permeability, but the effect of butanol on facilitated diffusion was inhibitory. A subsequent investigation by Hunter, George, and Ospina (1965) in which n-butyl alcohol and tannic acid were used, provided further help in distinguishing between simple and facilitated diffusion systems. This work suggested that a carrier system was present for glycerol in the erythrocytes of the rabbit, mouse, and man. During his study of hexose transport in beef erythrocytes, Laris (1967) noted considerable variation in the capacity of cells from different cattle to accumulate fructose both in the presence and in the absence of a metabolic inhibitor. Upon closer examination it was shown that beef erythrocytes could be divided into two distinct groups on the basis of differences in the fructose transport system. In a recent study, Hunger (1976) added six small mammals to the list of species in which a number of different nonelectrolytes penetrate the erythrocyte by facilitated diffusion. One of these six was the deer mouse (P. maniculatus), and it, like the other five species examined, was shown to have a carrier which is shared by glycerol and ethylene glycol. Hunger also obtained data which hinted at the possibility of permeability differences among separate populations of deer mice (Hunter, personal communication). Such findings prompted the present study of the permeability of red cells to glycerol in two different populations of the pinyon mouse (P. truei). In addition to this population comparison, the glycerol permeabilities of two closely related species, P. truei and P. californicus, were investigated

A study of the biogeography of Peromyscus maniculatus was undertaken in order to ascertain a few of the environmental parameters important in defining the distribution of this species and how the species in turn has adapted to these parameters. The Columbia Gorge was chosen as it presents a climatic gradient from maritime to continental with very little elevation gain. Changes along this gradient in topography, soils and vegetation community structure are discussed.

Organisms are constantly balancing energy demand with an adequate supply of oxygen and substrates to sustain metabolic activity. Thermogenesis is an important metabolic process by which endotherms predominately burn lipids to regulate and maintain their body temperatures by balancing heat loss with heat production. Due to their high rates of heat loss, small winter-active mammals, like the North American deer mouse (Peromyscus maniculatus), are constantly challenged with thermogenesis. Deer mice are also native to high-altitude environments, conditions that further complicate the process of thermogenesis due to the inherent reduced oxygen availability. How metabolic substrates are used for fuelling and sustaining thermogenesis at high altitude remains unclear. The goal of my thesis was to examine how lipid metabolism has evolved to sustain heat production in animals living in high-altitude environments. This was achieved by using deer mice native to high- and low-altitudes acclimated to either standard lab conditions or simulated high altitude (cold hypoxia). I demonstrate that during thermogenic capacity (cold-induced V̇O2max), high-altitude deer mice have higher thermogenic lipid oxidation rates compared to their lowland counterparts, which is further increased after cold hypoxia acclimation. Interestingly, these high rates of lipid oxidation were associated with higher circulatory delivery rates of fatty acids and triglycerides to thermo-effector tissues. Specifically, I show that after a bout of cold-induced V̇O2max, fatty acid uptake occurs primarily in the skeletal muscle in control acclimated high-altitude deer mice, and then shifts to brown adipose tissue following acclimation to high altitude conditions. These findings clearly show that in high-altitude deer mice, maximal thermogenesis is reliant on elevated delivery of circulatory lipids to muscle and brown adipose tissue. This research further sheds light on the mechanistic underpinnings responsible for enhanced thermogenic capacity of high-altitude deer mice and capacity for the highest lipid oxidation rates observed in any mammal. / Thesis / Doctor of Philosophy (PhD) / Thermogenesis, the metabolic production of heat, allows endotherms to maintain stable body temperatures in cold environments. However, it was not yet understood how small mammals fuel and sustain heat production in the cold and low oxygen environment of high altitude. My thesis has uncovered how deer mice native to high altitudes have adapted to burning fats at high rates in hypoxia to sustain thermogenesis. My findings show that high delivery rates of fats to heat-generating tissues are responsible for the elevated rates of heat production in high altitude deer mice. My work contributes to our understanding of the inner workings of the fat pathways and how it has evolved to ensure survival in extreme environmental conditions.

Thesis--University of Michigan. / Bibliography: p. 121-124.

No description available.

The objective of this study was to determine differences in small mammal assemblage structure and population dynamics among four oak dominated sites at four different stages of gypsy moth disturbance: a high tree mortality site, a disturbance in process site, a disturbance recovery site, and an undisturbed reference site. More specifically, the study was designed to identify changes in habitat structure that would influence small mammal microdistributions and determine the quality of habitat created by gypsy moth herbivory using demographic structure of <i>Peromyscus</i> populations as an indicator of habitat quality. <i>Peromyscus leucopus</i>, Peromyscus maniculatus, the Soricids, and <i>Clethrionomys gapperi</i> had greater abundances at the disturbed sites relative to the reference site. Gypsy moth disturbance increased the abundance of small mammals and the number of coexisting species within a given area, which was attributed to several changes in habitat structure. The disturbed sites were characterized as having more fallen logs and standing dead snags, greater shrub and herbaceous cover, and higher invertebrate abundances relative to the reference site. These changes in habitat structure provided small mammals with increased cover from avian predators, more food resources, and potential nesting cavities. <i>P. leucopus</i> populations at the high mortality site exhibited greater demographic stability than the reference Site populations. This was marked by higher proportions of females, smaller density fluctuations, more fall recruitment of young, higher residency, and lower proportions of males. Strong evidence for density-dependent population regulation was observed for <i>P. leucopus</i> populations at the high mortality site and the <i>P. maniculatus</i> population at the recovery site. At high densities these populations exhibited extensive intraspecific microhabitat segregation. Female adults segregated from juveniles and male adults into more optimal microhabitats. Male adult microhabitat use significantly differed from male juvenile microhabitat use. The exclusion of young mice from optimal microhabitats by adults may be a mechanism by which adults limit over-exploitation of resources by subordinate members of the population at high densities. The results of this study suggest that gypsy moth disturbance of areas dominated by chestnut oaks at least temporarily improves habitat quality for small mammals. / Master of Science

The pattern of geographic variation in tree-climbing ability of Peromyscus maniculatus was used as a natural experiment to examine the interaction of natural selection, genetic drift, and gene flow. The divergence in climbing behavior among lab-reared mice derived from adults trapped in forest, woodland, and desert habitats was compared with a series of adaptive and non-adaptive hypotheses of evolutionary change. Natural selection was predicted to produce better climbers in forests and woodlands than in deserts whereas divergence due to genetic drift was expected to be independent of habitat type. Gene flow between neighboring habitats was predicted to reduce differentiation in climbing traits. Tree-climbing ability was measured by determining the maximum diameter artificial trunk (rod) that a mouse could climb in escaping from a lighted, confined area. Larger diameter rod scores reflect better climbing abilities (Horner 1954). Comparisons of mean rod climbing scores between subspecies and among forest, woodland, and desert habitats reveal that P. m. rufinus, sampled from forest and woodland, is a better climber than P. m. sonoriensis, sampled from woodland and desert habitats. This is consistent with the hypothesis that natural selection has produced subspecies level adaptation in climbing behavior. However, the climbing ability of P. m. sonoriensis sampled from woodland habitats on isolated mountaintops, although slightly divergent from populations in adjacent desert scrub habitats, has not evolved in response to natural selection to the degree expected from the observed subspecies level adaptation. Additionally, populations of unknown subspecific status sampled from desert grassland habitat, adjacent to woodland P. m. rufinus, have climbing abilities that are not significantly different from woodland forms. Thus, evolution in certain populations is constrained. If gene flow from desert populations into woodland mountaintop populations is constraining evolution, then mountaintop populations should have high trait variances. Analysis of the within population variance does not support this hypothesis. Other lines of evidence that indicate gene flow is low or moderate are reviewed. In conclusion, adaptation to local habitats is constrained, perhaps by restrictive genetic correlations and/or lack of sufficient time to respond to natural selection for climbing ability. As a result, long periods of consistent selection are necessary to produce the pattern of subspecific adaptation in climbing behavior. (Abstract shortened with permission of author.)

Climatic and geographic events such as glaciations, island formation, river formation, and urbanization strongly affect habitat specialist species. By contrast, it is traditionally assumed that these events have little effect on habitat generalists but few studies have tested this assumption. In this study I sought to identify the effects of historic and contemporary biogeographic events on the genetic structure of a habitat generalist, the cotton mouse (Peromyscus gossypinus). This species is distributed throughout the southeastern United States, a region that has experienced dramatic geographic changes associated with both historic Pleistocene glacial cycles, as well as contemporary anthropogenic forces. In analyzing the genetic structuring in this species I took a telescopic approach, beginning with the patterns of variation throughout the species range from a phylogenetic standpoint. Using mitochondrial sequence data I identified three reciprocally monophyletic clades of the cotton mouse, a southeastern, northeaster, and western clade. Among these clades I identified eight distinct subspecies, four of which had previously not been identified using morphological characters. Of the four previously identified subspecies, this study resulted in a restructuring of the range of all except the Key Largo cotton mouse, which is restricted to northern Key Largo Florida. Secondly, I employed phylogeographic methods to examine the genetic patterns of the cotton mouse in a geographic context. Phylogeographic breaks in the cotton mouse are largely consistent with those observed in other taxa distributed throughout the southeastern United States. Geographic structuring in this species shows deep patterns associated with glacial maxima and minima of the Pleistocene period. Many of these patterns are maintained by contemporary geographic barriers to gene flow. Thirdly, I identified geographic structuring of genetic variation at a regional and local level. This structuring is partially due to the cotton mouse’s limited dispersal ability but is strengthened and reinforced by naturally occurring contemporary barriers to gene flow and contemporary anthropogenic forces which serve to limit dispersal in this species. Finally, I determined that urbanization has a dramatic negative effect on gene flow and genetic variation in this species on a local scale. Over a twenty year period populations in urban areas experienced a marked decrease in genetic variation while populations in non-urban areas experienced an increase in variation. During this time period, gene flow was effectively cut off among populations that had previously been panmictic. This study demonstrates that small mammal habitat generalists can be affected by both historic and contemporary climatic and geographic events at multiple geographic scales. These effects range from large scale geographic structuring throughout the species’ range to fine scale structuring associated with contemporary anthropogenic forces.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains ix, 114 p. : ill. (some col.), map. Includes abstract. Includes bibliographical references (p. 92-107).