Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 198-229).

Golden mice (Ochrotomys nuttalli) are generally an elusive and rare species throughout their geographic range in the southeastern United States. They are considered to be habitat specialists that prefer dense understory consisting of shrubs and vines. Golden mice are less vagile, and likely disperse shorter distances than other sympatric species such as the white-footed mouse (Peromyscus leucopus). Conversely, white-footed mice are considered habitat generalists that inhabit a variety of habitat types, are more vagile, and disperse farther than golden mice. Because of this it is likely that golden mice have a lower genetic diversity and are more genetically subdivided than white-footed mice. In southern Illinois, golden mice are on the periphery of their range, which is one of the reasons they are on the state-threatened list in Illinois. It has been hypothesized that populations on the periphery of a species range will have more population structure and lower genetic diversity than populations in the core of the range. Tissue samples for golden mice and white-footed mice were collected from 24 sites throughout southern Illinois and 24 sites throughout the golden mouse core range. I analyzed 13 and 10 microsatellite markers as well as 594 and 624 base pairs of the mitochondrial control region for golden mice and white-footed mice, respectively, to characterize and compare the genetic diversity and population structure of both species. Overall haplotype diversity (0.76) and nucleotide diversity (0.20%) was lower in golden mice compared to white footed mice (0.99 and 1.97%). Results of an AMOVA using the mitochondrial control region revealed more subdivision among the 3 populations of golden mice (Φst = 0.099, P < 0.001) than among the 3 populations of white-footed mice (Φst = 0.058, P < 0.001). Microsatellite loci showed a similar trend with overall FST values of 0.027 (P < 0.001) for golden mice and 0.004 (P = 0.137) for white-footed mice. I intended to compare golden mouse individuals from southern Illinois and the core of the range, but too few individuals were collected from the core. More samples need to be collected throughout the core of the range to better understand the population genetics of golden mice in the core of the range compared to the periphery.

Oak-dominated forest has declined in the eastern United States as shade-tolerant species (e.g., maple [Acer spp.]) replace oaks (Quercus spp.), sparking concern among ecologists regarding species that consume acorns. My goal was to describe how increasing mesophication of oak forests may affect consumers in higher trophic levels. I investigated relationships among forest composition, mast production, small-mammal density, and carnivore occurrence in 8 stands representing 4 forest types (upland oak, mixed-mesophytic, non-oak, and bottomland oak) in southern Illinois. I calculated tree-species richness, basal area, and other measures of forest composition using 3 0.04-ha plots/stand. In June-August 2009 and 2010, I live-trapped small mammals for 16,236 trap-nights with trapping webs to estimate population density of mice (Peromyscus spp.). I collected mast seeds during October-November 2009 and 2010 and calculated average dry biomass (g/m2) for each species and stand. During winter 2009-2011, I photographed carnivores using baited camera traps and combined these data with those from stands used in a concomitant large-scale carnivore survey. I regressed mast biomass, Peromyscus density, Peromyscus survival, and carnivore occurrence on measures of forest composition and hard-mast biomass. Peromyscus summer density was not related to % hard-mast basal area, nor to hard-mast biomass from the previous autumn. Survival of Peromyscus in 2010 displayed a significant positive relationship with hard-mast biomass in 2009 (F1,6 = 7.85, P = 0.04, r2 = 0.61). Logistic regressions of carnivore occurrence on Peromyscus density were not significant. Coyote (Canis latrans) occurrence at my sites and additional sites during January-April 2010 decreased with increasing % hard-mast basal area (x2 = 4.64, df = 1, P = 0.03). Bobcat (Lynx rufus) and gray fox (Urocyon cinereoargenteus) occurrence showed no relationship with % hard-mast basal area. Many other studies have demonstrated links of several species to oak forest, but the scale of this study may have been too small to detect effects of mesophication. Alternatively, small-mammal density may be influenced by invertebrate prey abundance or weather conditions. The landscape matrix of oak-hickory forest may also act to homogenize Peromyscus density across my study sites. Longer-term research could help clarify relationships among trophic levels. It is important for managers to consider techniques that may conserve oak forest.

Various aspects of performance (e.g., sprint speed, grip strength) are thought to be important determinants of the success of animals in natural activities such as foraging, mating, and escaping from predators. However, it is generally known that morphological properties enhancing one type of performance (e.g., speed) can lead to a reduction in another (e.g., strength). Such performance trade-offs have been quantified at the inter-specific level, but evidence at the inter-individual level remains equivocal. To test for the presence of a performance trade-off, I initiated a study on wild white-footed mice (Peromyscus leucopus). In summer 2016, I captured a total of 186 individuals, 87 of which were repeatedly phenotyped for grip strength and sprint speed. A significant positive relationship was found between body mass and grip strength (but not for sprint speed). Individual differences in performance were repeatable through time for both grip strength and sprint speed. Using a bivariate mixed model, I detected a significant negative correlation between grip strength and sprint speed at the among-individual level. By contrast, the within-individual correlation between grip strength and sprint speed tended to be positive, suggesting that some unquantified aspects of the mouse phenotype (e.g., body condition, age) may have a positive effect on both performance traits. Given the relatively low repeatability of grip strength and sprint speed, a failure to properly partition the correlation at the among- and within-individual level generates a counter-intuitive, positive correlation. This study is one the first to detect a performance trade-off at the among-individual level in a wild animal population.

The marine ecosystem provides key resources to terrestrial organisms inhabiting oceanic islands. These subsidies of marine resources have the potential to affect species richness, ecology and productivity, especially on islands with high perimeter-area ratios. I investigated the impact and importance of marine subsidies on mammal diversity and diet on islands of British Columbia’s Central Coast. Insular mammal species richness was significantly correlated with island area and quantity of marine subsidy (wrack). However, mink and river otter island occupancy was unaffected by island-level covariates, whereas small mammals were more likely to occupancy islands closer together. Keen’s mice and food items were subsidized directly (i.e., consumption) and indirectly (i.e., fertilization) by marine resources. Beach-dwelling arthropods composed 33% of mouse diets. Furthermore, mouse and terrestrial arthropod abundances and stable isotope signatures (d13C and d15N) of food items were depleted moving inland from the beach. Finally, reproductive male mice consumed up to twice the marine-derived prey as females. Collectively, this work demonstrates that insular mammalian richness, as mediated by island-level factors, may be complex due to variation within populations and the recipient ecosystem (e.g., prey biomass). / Graduate

Host-parasite interactions are complex, involving host behaviour, host condition, and possible antagonism or mutualism between co-occurring parasites. The white-footed mouse (Peromyscus leucopus) is a small, abundant, generalist rodent, and the primary host for the black-legged tick (Ixodes scapularis) in its larval stage. Since larval ticks do not actively pursue their hosts (they wait for possible hosts to come to them), individual differences in mouse exploratory behaviour might be expected to correlate with tick burden. However, mice may also prevent tick attachment with defensive behaviour such as grooming. Yet, the relationships between tick parasitism and host exploratory and grooming behaviours have never been assessed. I analysed data from a capture-mark-recapture study conducted over 5 summers (2016-2020) in eastern Ontario, Canada, in which 1,035 mice were captured a total of 4,333 times. The probability of tick parasitism occurring and being more intense was significantly higher when the mouse was also parasitized by fleas, suggesting co-occurrence of these two parasites on host mice. A total of 510 mice were subjected to an open-field test to quantify exploratory and grooming behaviours. Exploration had a negative relationship with tick presence and a positive relation with flea presence. Most interestingly, there was a significant “tick × flea” interaction on exploratory behaviour such that fleas were positively associated with exploration only when ticks were absent. Surprisingly, there was no relationship between grooming behaviour in the open-field test and parasite presence, although grooming increased with mouse activity. This study shows that co-occurring parasite species (ticks and fleas) may interact to affect their host’s exploratory behaviour. Alternatively, individual differences in exploratory behaviour of hosts may differentially affect their susceptibility to being infested with ticks, fleas, or both. Future manipulative studies should use experimental design to determine the causality of the parasitism-behaviour relationships observed.

The perception of increased predation risk by nocturnal mice and other small mammals has been shown to reduce activity levels, particularly in foraging effort. Various cues of predation risk have been used in previous studies, but few have assessed the potential interactions between different types of cues. I conducted field, laboratory, and enclosure experiments using predator scents, artificial light, and microhabitat variables to determine the effects of direct and indirect cues of predation risk on foraging behavior in wild nocturnal mice. Experimental foraging trays served as artificial resource patches, and giving-up densities were measured in order to test for foraging persistence in patches exposed to cues of predation risk. Cotton mice (Peromyscus gossypinus) were used in laboratory and enclosure trials, and were the most common mice present at the sites used for field trials. Although previous foraging studies have used other Peromyscus species, this species has not been tested, but ranges over densely populated areas of the United States where artificial light could potentially affect its behavior. In outdoor and laboratory enclosures, cotton mice showed no aversive response to bobcat urine, cloths rubbed on cats, or snake sheds, but did exhibit avoidance of cat fur and artificial light. In the field experiment, mice showed a strong preference for covered microhabitats, but did not avoid bobcat urine or artificial light. Foraging in artificial resource patches also increased throughout the duration of the field experiment, possibly coinciding with a reduction in naturally-available forage. Mice in this population appear to use cover as their primary means of avoiding detection or capture by predators, though they do avoid artificial light and at least one fur-derived odor when their available options for escape are reduced.

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.

Members of the genus Peromyscus, White-footed Mice, are known to occur in nearly all habitats of North America. Because of their numerical abundance and widespread distribution, these mice are extensively used in the study of the dynamics of animal populations. Thus, information perteining to the local distruibution and activities of these mice is of value to the more comprehensive studies that are being carried out in the field of zoological research.

Island isolation can cause changes in body size, cranial characteristics, and genetic variation in mammals. We use geometric morphometrics to test skull and mandible shape and size change across three species of endemic Cozumel Island rodents in order to test the “island rule” of larger size in isolated rodents. We also sequenced the D-Loop and cytochrome b region of the mitochondrial genome and tested for differences in genetic variation between island and mainland groups, as well as population structure and gene flow in order to assess the effect of island isolation on these three rodents. We found that the three species of rodents showed varying degrees of size and shape differences from island to mainland with some species varying considerably and others not at all. The genetic results were similar with some species exhibiting potential founder effects, while others showed little differentiation between the island and mainland. We conclude that evolution on islands is highly conditional on the history, community composition, and biology of the colonizing species.