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.

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.)

Intraspecific phylogeography and the phylogenetic relationships of recently-diverged taxa are best assessed with the use of a genetic marker that coalesces rapidly and thus provides phylogenetically informative characters for closely-related taxa. Mitochondrial DNA (mtDNA) fits these criteria and was thereby ideal for analyzing genetic variation within and among the youngest taxonomic members of the Peromyscus maniculatus species group, P. sejugis (restricted to two islands in the Sea of Cortés), P. maniculatus (distributed throughout North and Central America) and P. keeni (a coastal species restricted to the Pacific Northwest of North America). The approach utilized in this research involved sequencing a 1439 base-pair (bp) region of mtDNA for a total of 581 specimens representing 45 different geographic localities from along the west coast of North America. The sequences obtained were used to assess the partitioning of genetic diversity within and among these taxa, address phylogenetic and taxonomic concerns about the western representatives of the P. maniculatus species group and discuss the post-Pleistocene biogeography of the west coast of North America. Analysis of mtDNA sequence variation, considered within the framework of a phylogenetic species concept, revealed the existence of two evolutionarily significant units of P. sejugis as well as a previously unrecognized sibling species nested within the Pacific coastal range of P. maniculatus. Moreover, analysis of intraspecific sequence divergence allowed for the identification of the ice-free refugium thought to harbor P. keeni throughout glaciation during the Pleistocene epoch. This work will establish the foundation for additional examination of cryptic genetic variation in different morphotypes of P. maniculatus and continue the precedent for recognizing P. maniculatus-group taxa that reflect true evolutionary entities.

Intraspecific phylogeography and the phylogenetic relationships of recently-diverged taxa are best assessed with the use of a genetic marker that coalesces rapidly and thus provides phylogenetically informative characters for closely-related taxa. Mitochondrial DNA (mtDNA) fits these criteria and was thereby ideal for analyzing genetic variation within and among the youngest taxonomic members of the Peromyscus maniculatus species group, P. sejugis (restricted to two islands in the Sea of Cortés), P. maniculatus (distributed throughout North and Central America) and P. keeni (a coastal species restricted to the Pacific Northwest of North America). The approach utilized in this research involved sequencing a 1439 base-pair (bp) region of mtDNA for a total of 581 specimens representing 45 different geographic localities from along the west coast of North America. The sequences obtained were used to assess the partitioning of genetic diversity within and among these taxa, address phylogenetic and taxonomic concerns about the western representatives of the P. maniculatus species group and discuss the post-Pleistocene biogeography of the west coast of North America. Analysis of mtDNA sequence variation, considered within the framework of a phylogenetic species concept, revealed the existence of two evolutionarily significant units of P. sejugis as well as a previously unrecognized sibling species nested within the Pacific coastal range of P. maniculatus. Moreover, analysis of intraspecific sequence divergence allowed for the identification of the ice-free refugium thought to harbor P. keeni throughout glaciation during the Pleistocene epoch. This work will establish the foundation for additional examination of cryptic genetic variation in different morphotypes of P. maniculatus and continue the precedent for recognizing P. maniculatus-group taxa that reflect true evolutionary entities.

The available data examining the influence of rotational grazing on rodent responses are limited. This study investigated how rotational livestock grazing practices influence small mammal rodent abundances and species diversity. We looked for evidence of variation in the occurrence and/or numbers of certain rodent species among three plant community types (grassland, shrubland, grass-shrub mix), managed with or without grazing. We used Sherman live traps over a total of eight trapping sessions. We totaled 486 trapnights for each of the six plant community and grazing management combinations. The three plant community types were identified by visual cover. Out of the eight different species we captured, only Peromyscus maniculatus (North American deermouse) and Reithrodontomys megalotis (western harvest mouse) had sufficient captures to be analyzed for differences in abundance. Using all eight species to calculate the Shannon’s diversity index for each plot, we found evidence that rodent species diversity is less in grassland habitats than in shrubland habitats or grassland/shrubland mixed habitats (p

The purpose of this study is to compare two populations of Peromyscus maniculatus gambelii from the same location, separated by about 80 years in an attempt to determine the degree of dissimilarity between them.

The Quotient Method (QM), a laboratory-based risk assessment methodology used by the Environmental Protection Agency to evaluate pesticides for registration and use, has not been thoroughly field-tested and its performance has not always been reliable. My objective was to determine if variation in vegetation structure or diet of exposed animals could result in adverse ecological effects that were not predicted by the QM. In April and early May 1993, I established populations of herbivorous gray-tailed voles (Microtus canicaudus) and omnivorous deer mice (Peromyscus maniculatus) in 24 0.2-ha enclosures planted with alfalfa (Medicago sativa). Alfalfa in 12 enclosures was mowed on 22 June to reduce vegetation height. Small mammal populations were monitored by live trapping from May through August 1993. On 14 July, an organophosphorus insecticide, azinphos-methyl, was applied at 0, 0.88, and 3.61 kg/ha. Insecticide residues were measured on canopy-level spray cards, soil samples, and alfalfa. I compared the observed residue concentrations with predictions based on the nomogram used to estimate exposure for QM risk assessments. I also compared QM predictions of risk with observed effects on population size and growth, survival, reproductive activity, recruitment, body growth, movements, and diet of the small mammals. Much of the insecticide reached ground level in mowed enclosures, but dense alfalfa intercepted most of the spray in unmowed enclosures. The mean half-life of azinphos-methyl on alfalfa was 3.4 days and was not affected by mowing. Mean residue concentrations on mowed alfalfa and the top 15 cm of unmowed alfalfa were underestimated by the QM exposure nomogram. Therefore, pesticides may pose greater risk to organisms inhabiting sparse vegetation or the tops of plants than predicted by the QM. Treatment with azinphos-methyl at 3.61 kg/ha caused severe effects in both mowed and unmowed enclosures on population size and growth, survival, recruitment, and body growth of voles. Effects of azinphos-methyl on vole recruitment and body growth and on survival of female voles were greater in mowed than in unmowed enclosures. However, I did not find that population-level responses of voles to the chemical differed between mowing treatments. Most effects on voles were of short duration (<27 days) but vole densities in 3.61 kg/ha enclosures remained depressed >6 weeks after spraying. The 3.61 kg/ha application rate resulted in a 42% decrease in deer mouse densities in mowed enclosures during the week of spraying, but the insecticide had no adverse effects on deer mice in unmowed enclosures. In addition, the insecticide may have reduced recruitment of deer mice in mowed enclosures. Analysis of deer mouse feces indicated that consumption of arthropods increased in insecticide-treated enclosures just after spraying occurred. Survival, reproductive activity, body growth, and movements of deer mice were highly variable and not significantly affected by azinphos-methyl. Mowing resulted in greater residue concentrations than predicted and, consequently, the insecticide adversely affected voles and deer mice in mowed enclosures at application rates characterized as low risk by the QM. However, food aversion or selective feeding on alfalfa tops may have resulted in similar exposure of voles to the 3.61 kg/ha treatment in mowed and unmowed enclosures. I did not find that insectivorous feeding behavior of deer mice made them more susceptible than predicted. Although residue concentrations on alfalfa did not follow predictions, the gross pattern of effects on small mammals was consistent with QM risk characterization. However, the QM may underestimate exposure and risk when pesticides are sprayed on sparse vegetation. / Graduation date: 1995

Wild-trapped and laboratory-reared Peromyscus maniculatus (Wagner) were raised as confined colonies indoors with various stocking densities ranging from 0.026 to 0.100 mice per sq. ft. in pens of 40, 77, and 154 sq. ft. The animals were individually tagged and all pens were censused at weekly or semi-monthly intervals to record animals present, body weights, food consumption, and overt reproductive condition. At the termination of each experiment, all mice were necropsied and organ weights of gonads and adrenals recorded. Histological sections were made of the testes and ovaries. Half the colonies were subjected to density-independent exploitation by removal of 50% of the mice in each litter before weaning. Colonies stocked with the wild-trapped P. m. rufinus failed to establish a regular pattern of successful breeding and were terminated after one year. The succeeding colonies were stocked with the lab-reared P. m. sonoriensis and these did breed regularly, and the young survived to maturity. Reduction of the population growth rate to zero at the equilibrium density was accomplished by a cessation of breeding by the original females after an average of 2.9 litters was produced by each female. This, combined with a failure of the progeny born into the colony ever to produce young, caused the population growth rate to remain at zero for up to the maximum of 52 weeks permitted in this experiment. The exact mechanism appears to be psycho-physiological in nature, in that regression of the germinal tissues of the adults occurs, and these tissues failed to mature in the progeny in all experiments. Reduction of the population growth rate to zero at equilibrium density is not accomplished by mortality of either young or adults, except when wild-trapped mice are used. Density-independent exploitation of the colonies increased the number of litters born, the litter size, and the total number of young born. There was a tendency for higher pre-weaning mortality. The net effect of these changes was a tendency for reduction in the equilibrium density of the exploited colonies, which may indicate that this species under these conditions is not totally self-regulatory; i.e., equilibrium density may be determined by both intrinsic and extrinsic factors. There was no discernible effect of exploitation on the measures of body weight, food consumption, adrenal weight, or adrenal weight per gram of body weight. Many parameters were found to be negatively correlated with stocking density: the length of the reproductive period, numbers of litters born in a colony, total number of young born in a colony, litter size, number of nest boxes occupied by the mice at equilibrium, and the number of mice present in a colony at equilibrium. Some physiological measures proved to be positively correlated with density: progeny weight at three months, adrenal weight, and adrenal weight per gram of body weight.

No description available.