Peromyscus Maniculatus Gracilis Research Articles

Patterns of acorn selection in Peromyscus mice and possible implications in a changing climate

Abstract Rodents play a key role in forest regeneration by dispersing seeds and interspecific differences in seed preferences could have important consequences for forest growth. The White-footed Mouse (Peromyscus leucopus) and Deer Mouse (Peromyscus maniculatus gracilis) are 2 closely related species that can exploit Red Oak (Quercus rubra) acorns but may display different preference levels due to the high tannin concentration present in these acorns. Here we investigated how White-footed Mice and Deer Mice differ in their ability to exploit Red Oak acorns. We conducted a cafeteria-style experiment where we offered mice (n = 61) acorns of Red Oak and Bur Oak (Q. macrocarpa; control seed with lower tannin levels) and video-recorded their preference and the acorn fate (consumed or cached). Using mixed-effects models, we found that both mouse species selected and consumed Bur Oak acorns at a high rate; however, White-footed Mice were 6.67 times more likely to select and consume Red Oak acorns than Deer Mice. Furthermore, White-footed Mice tended to cache Red Oak acorns near the surface where there is a higher chance of germination, while they usually consumed Bur Oak acorns. Our results suggest that Red Oaks have a better strategy for avoiding predation than Bur Oaks (i.e., high tannin levels leading to caching), and the strong interaction between the White-footed Mouse and Red Oak might be an important mechanism behind the current range expansion of both species in response to climate change.

Peromyscus maniculatus (Rodentia: Cricetidae): An overlooked reservoir of tick‐borne pathogens in the Midwest, USA?

AbstractMice belonging to the genus Peromyscus are one of the most important reservoirs of tick‐borne pathogens in the United States. However, the composition and abundance of Peromyscus species may vary geographically. The woodland deer mouse, Peromyscus maniculatus gracilis, is often abundant in the northern counties of Minnesota, Wisconsin, and Michigan. In these states, multiple pathogens transmitted by the blacklegged tick, Ixodes scapularis, are endemic. In comparison to the well‐studied white‐footed mouse, Peromyscus leucopus, little is known about the importance of P. maniculatus in maintaining natural cycles of tick‐borne pathogens. We conducted small mammal trapping in north‐central Wisconsin and compared the modified reservoir potential of P. maniculatus to P. leucopus. Based on mixed‐model regression analysis, individual P. maniculatus were 2.07 (1.07–4.01) times more likely to be infected with Borrelia burgdorferi compared with P. leucopus. We report the first detection of three emerging tick‐borne pathogens (Babesia microti, Borrelia mayonii, and Ehrlichia muris eauclairensis) in P. maniculatus. Additionally, P. maniculatus infected with Ba. microti were 4.8 (2.74–8.50) times more likely to be concurrently infected with Bo. burgdorferi compared with P. leucopus. While we found individual P. leucopus to be more infested with both larval and nymphal I. scapularis, P. maniculatus was the more abundant species. As a result, P. maniculatus had a higher modified reservoir potential in our study area and was likely responsible for feeding and infecting more ticks with pathogens than P. leucopus. Overall, our results illustrate that P. maniculatus is an important reservoir in areas of the Midwest, where it occurs in high abundance.

Personality and behavioral syndromes in two Peromyscus species: presence, lack of state dependence, and lack of association with home range size

One common theme of adaptive hypotheses for the existence of stable individual differences in behavior (personality) or persistent correlations among behaviors (behavioral syndromes) is an association between intrinsic state (e.g., body size, mass, metabolism) and the behavioral traits of interest. Empiricists are tasked with assessing whether there is an association between intrinsic state and behavior, but the statistical methods to appropriately quantify the among-individual correlation between intrinsic state and behavior have only recently become widely known. We conducted a multiyear study in wild mice of two Peromyscus species (Peromyscus leucopus noveboracensis and Peromyscus maniculatus gracilis) to assess the existence of stable individual differences in four different behaviors (presence of animal personality, as assessed by quantifying repeatabilities) and one measure of intrinsic state (body mass), the degree of association between these four behaviors (presence of behavioral syndromes), and the association of these behavioral traits with body mass using multivariate methods that allowed us to estimate the within-individual (residual) component and the among-individual component. We used standardized behavioral tests to measure struggle time (time spent struggling when removed from the trap) and exploration time (time spent exploring a novel surface) and used open-field trials to measure whether or not an individual entered the open field plus the total time it spent active in the open field. In P. leucopus, we assessed whether coarse but quick methods of assessing animal personality (struggle or exploration time) correlate with behavior using more in-depth estimates obtained by open-field trials. Additionally, we tested the ecological relevance of our personality measures by assessing their association with home range size in P. leucopus. In both species, struggle time, exploration time, and body mass were significantly repeatable and there was a significant among-individual correlation between struggle time and exploration time. However, in both species, there was no evidence for an among-individual correlation between our measure of intrinsic state (body mass) and personality traits. In one species (P. leucopus), we found that individuals that spent more time struggling or exploring a novel surface were also more likely to emerge into an open field and spent more time being active in an open field, but these four behavioral measures were not associated with home range size. Our results suggest among-individual correlation among these different behaviors but no among-individual correlation between behavior and intrinsic state. Over the past 15 years, it has become clear that nonhuman animals exhibit “personalities”: some individuals consistently differ in their behavior, and there is limited flexibility in their behavior when they experience environmental change. Biologists have now been searching for why and how animal personalities exist and their ecological and evolutionary consequences. Some explanations have focused on how condition or “internal state” may cause variation in animal personalities. In this study, we show that two species of wild mice exhibit personalities and that their personality traits are associated with one another, in that mice that were less docile were also more active, exploratory, and bold. We then show that their personality traits were not linked with body mass, suggesting a lack of association between internal state and personality. Our results provide important insights into the causes of personality in nonhuman animals.

Effects of Range Contraction and Habitat Fragmentation on Genetic Variation in the Woodland Deer Mouse (Peromyscus maniculatus gracilis)

Abstract Recently, the range of the woodland deer mouse (Peromyscus maniculatus gracilis) in Michigan's Lower Peninsula (LP) has contracted simultaneously with the increasing abundance of the white-footed mouse (Peromyscus leucopus). The known LP range of P. m. gracilis has shrunk to two areas, one in Cheboygan/Otsego Counties and another in Alpena County. We used a Geographic Information System habitat analysis to predict where P. m. gracilis could be found between those areas and trapped at selected locations. P. leucopus was present at every location, but the known range of P. m. gracilis had expanded only slightly, and remains as two separate fragments. We analyzed 11 microsatellite loci for all P. m. gracilis to investigate the genetic structure of their remaining LP populations. Genetic diversity was high, FST values were low, and there was no evidence of recent bottlenecks, indicating that LP populations of P. m. gracilis once had extensive gene flow across the entire region. However, trapping data...

Seeds of doubt: feeding preferences of white-footed deer mice (Peromyscusleucopus noveboracensis) and woodland deer mice (Peromyscusmaniculatus gracilis) on maple (genusAcer) seeds

This study explores foraging choices made by seed predators (white-footed mouse, Peromyscus leucopus noveboracensis (Fischer, 1829), and woodland deer mouse, Peromyscus maniculatus gracilis (LeConte, 1855)) presented with seeds of two dominant tree species (sugar maple, Acer saccharum Marsh., and red maple, Acer rubrum L.). I hypothesized that both species would prefer A. saccharum seeds, as they are larger and ostensibly contain more energy. Although P. l. noveboracensis consumed more seed than P. m. gracilis, there was also a species-specific difference in preference. Peromyscus maniculatus gracilis clearly preferred A. rubrum over A. saccharum, whereas preferences of P. l. noveboracensis were less specific. Peromyscus leucopus noveboracensis, being a habitat generalist, may demonstrate higher plasticity in response to different food types. Peromyscus maniculatus gracilis may prefer A. rubrum because of differences in nutrition, handling costs, or germination schedules, although this was not explicitly tested. This species-specific difference in preference indicates the common assumption that Peromyscus species are ecologically similar should be made with caution.

Seasonal plasticity of maternal behaviour in Peromyscus maniculatus

Individual variation in maternal care has been shown to have important consequences for offspring behaviour, development, and physiology. The proximate mechanisms associated with these maternal effects have been elegantly detailed in laboratory rodents where environmental variation is typically minimized. However, investigating the ultimate consequences of differences in maternal behaviour and factors that maintain variation in maternal care requires the extension of well established protocols for measuring maternal behaviour in the lab to a wild rodent species. In the present study we build on the important contributions of laboratory research by applying laboratory protocols for quantifying maternal behaviour, maternal provisioning, and maternal responsivity in laboratory rodents to wild-caught Peromyscus, which experience large fluctuations in environmental conditions. We temporarily transported wild-caught deer mice (Peromyscus maniculatus gracilis) to a field laboratory for parturition and the first week post partum and then returned individuals with their offspring to the wild. We demonstrate that the proportion of time spent nursing by wild-caught deer mice was similar to previous studies of laboratory rodents and was repeatable within litters. However, in contrast to prior studies of laboratory rodents, the proportion of time spent nursing by wild-caught deer mice was independent of the proportion of time spent licking and grooming and the latency to retrieve pups in a pup-retrieval test. Wild-caught deer mice also exhibited a high degree of seasonal plasticity in nursing behaviour; females that raised litters early in the season spent almost twice as much time nursing as those raising litters at the end of the season. The amount of time spent nursing offspring in captivity was negatively correlated with population density of wild mice in the field at the time of their capture, but such a seasonal decline in nursing could also be caused by other seasonal changes in their natural environment. These findings suggest the potential for much greater plasticity in maternal care by rodents than might otherwise be revealed from studies of animals born and raised under controlled laboratory conditions.

Microsatellite Genetic Structure and Cytonuclear Discordance in Naturally Fragmented Populations of Deer Mice (Peromyscus maniculatus)

The Great Lakes impose high levels of natural fragmentation on local populations of terrestrial animals in a way rarely found within continental ecosystems. Although separated by major water barriers, woodland deer mouse (Peromyscus maniculatus gracilis) populations on the islands and on the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan have previously been shown to have a mitochondrial DNA contact zone that is incongruent with the regional landscape. We analyzed 11 microsatellite loci for 16 populations of P. m. gracilis distributed across 2 peninsulas and 6 islands in northern Michigan to address the relative importance of geographical structure and inferred postglacial colonization patterns in determining the nuclear genetic structure of this species. Results showed relatively high levels of genetic structure for this species and a significant correlation between interpopulation differentiation and separation by water but little genetic structure and no isolation-by-distance within each of the 2 peninsulas. Genetic diversity was generally high on both peninsulas but lower and correlated to island size in the Beaver Island Archipelago. These results are consistent with the genetic and demographic isolation of Lower Peninsula populations, which is a matter of concern given the dramatic decline in P. m. gracilis abundance on the Lower Peninsula in recent years.

North American Deer Mouse, <em>Peromyscus maniculatus</em>, Consuming a Parasitizing Botfly Larva, Diptera: Cuterebridae

During a laboratory study in Algonquin Provincial Park, Ontario, Canada, I videotaped a female North American Deer Mouse, Peromyscus maniculatus gracilis, consuming a botfly larva, Family Cuterebridae, that had just emerged from her chest. Although botfly parasitism has been widely studied in several species of small mammals, there are no prior reports of the host consuming the emerged botfly parasite.

Field Identification of the Mice <em>Peromyscus leucopus noveboracensis</em> and <em>P. maniculatus gracilis</em> in Central New York

Field identification of the White-footed Mouse (Peromyscus leucopus noveboracensis) and Long-tailed Deer Mouse (Peromyscus maniculatus gracilis) is difficult because of their similar external morphology. Peromyscus were sampled by live-trapping during a five-year period (1992-1996) at the Arnot Teaching and Research Forest, Van Etten, New York and identified to species by electrophoresis of their salivary amylase. No electromorphs were shared between P. leucopus and P. maniculatus, thus permitting unambiguous species identification of individuals. Means and ranges of four external measurements (ear, head-body, hind-foot, and tail) and tail to head-body ratio were determined for amylase-genotyped live mice. Although some body measurements did differ on average between the two species (ear, head-body, and tail for adults; hind-foot and tail for juveniles), the ranges of these overlap considerably. When the four external measurements (excluding the tail to head-body ratio) were used to construct two discriminant-function equations, they yielded correct identification of 80% of the adult P. l. noveboracensis and P. m. gracilis assessed excluding juveniles, and 71% of adult and juvenile mice combined. The function reported here allows partial field identification, but genetic analysis remains the only reliable field method for differentiation between live P. l. noveboracensis and P. m. gracilis. Includes erratum for a figure in this article.

Fecal corticosteroids in agouti and non-agouti deer mice ( Peromyscus maniculatus)

Total and per gram fecal corticosteroid concentrations were determined for agouti and non-agouti deer mice ( Peromyscus maniculatus gracilis) over 24 h under normal caging conditions and after exposure to the stress of novel caging. Per gram corticosteroid concentrations, fecal output, and 24-h corticosteroid production were greater in stressed compared with unstressed deer mice of both color morphs, whereas stressed agoutis had a greater increase in per gram corticosteroid concentrations when compared with non-agoutis. However, due to increased fecal output, stressed non-agouti deer mice had greater 24-h corticosteroid production. Thus, agouti and non-agouti deer mice differ in their hormonal reaction to stress. This is the first demonstration of corticosteroid differences associated with the agouti locus.

Body and organ mass in agouti and non-agouti deer mice ( Peromyscus maniculatus)

Body, adrenal, brain, heart, liver, kidney, spleen and testis masses were determined for agouti and non-agouti deer mice ( Peromyscus maniculatus gracilis) of both sexes. Body mass was highest for non-agouti females and lowest for agouti females; and sex differences in body mass were significant for agouti, but not non-agouti, deer mice. Adrenal, brain and liver masses were similar between color morphs; heart mass was greater in agouti males; and kidney, spleen and testis masses were all significantly greater for non-agouti deer mice. Splenomegaly in non-agouti deer mice was prominent, as spleens of non-agouti deer mice were 50% larger than those of agouti animals. Sex differences varied across organs and color morphs. For both color morphs, males had heavier adrenals and brains, whereas females had heavier livers and spleens. Kidney and heart mass was greater for female non-agouti deer mice, but for agouti animals, heart mass was greater in males and kidney mass differed little between the sexes. For both color morphs, testes and spleen mass was altered by photoperiod in 72 deer mice housed under short- or long-day conditions and the effect was stronger in non-agouti animals. This is the first report of splenomegaly and sex-specific body mass differences associated with the non-agouti allele.

Population variation in the metabolic response of deer mice to infection with Capillaria hepatica (Nematoda)

The effects of parasites on their hosts can vary among host populations, but few studies have examined geographic variation in host-parasite interactions. We examined the effects of Capillaria hepatica (Nematoda) infection on deer mice (Peromyscus maniculatus gracilis) from two different populations. Specifically, we measured the basal metabolic rate (BMR), cold-stress maximum oxygen consumption (MRpeak), metabolic scope (MRpeak/BMR), and thermogenic endurance of infected and uninfected mice from one population with, and a second population without, a history with C. hepatica. Infection had no effect on BMR, but did have effects on cold-stress measures. A previous study documented a significant relationship between survival and MRpeak in wild deer mice; hence, the effects of infection on the parameters that we measured could influence fitness. Only mice that had no historical association with C. hepatica displayed negative consequences of infection, which suggests that the historical host population has evolved mechanisms to cope with infection. Models of the evolution of virulence should include evolutionary responses of both hosts and parasites, particularly when systems involve macroparasites that have long generation times.

Physiological Responses of Deer Mice (Peromyscus maniculatus) to Infection with Capillaria hepatica (Nematoda)

Negative effects due to infection have not been documented for most natural host-parasite associations. I performed an infection experiment to measure the physiological consequences of infection by Capillaria hepatica in deer mice (Peromyscus maniculatus gracilis). Compared to their uninfected siblings, infected mice displayed increased serum concentrations of alkaline phosphatase and total proteins and reduced concentrations of albumin. Infected mice also had higher hematocrits and enlarged livers and spleens. There was no difference in swimming endurance between infected and control animals, possibly because mice did not perform at maximum aerobic capacity. Sex differences in alkaline phosphatase and albumin levels suggest that females are more sensitive to similar burdens of C. hepatica. Different hematocrit responses between mice from 2 localities suggest that historical associations can lead to evolutionary change in pathophysiology caused by this nematode. Further experiments would reveal whether these disturbances lead to reductions in host fitness.

The agouti coat-color locus may influence brain catecholamines: Regional differences in norepinephrine and dopamine in the brains of two color-morphs of deermice ( Peromyscus maniculatus)

Levels of norepinephrine (NE) and dopamine (DA) were measured by HPLC from the cortex, striatum and brain stem of agouti and nonagouti deermice ( Peromyscus maniculatus gracilis). In the brain stem, agouti animals exhibited significantly higher NE whereas nonagouti animals had significantly higher DA. In contrast, agouti deermice had nearly twice the DA levels of nonagouti animals in both the cortex and striatum. Levels of cortical and striatal NE were similar in both color morphs, although NE in nonagouti animals was 8% higher and less variable. The variability of both NE and DA was much lower in the brain stem than in either the striatum or the cortex. This is the first evidence of a pleiotropic effect of the agouti coat-color locus on brain catecholamines.

ENU and radiation-induced reverse mutations recovered in mice

Body, adrenal, brain, heart, liver, kidney, spleen and testis masses were determined for agouti and non-agouti deer mice (Peromyscus maniculatus gracilis) of both sexes. Body mass was highest for non-agouti females and lowest for agouti females; and sex differences in body mass were significant for agouti, but not non-agouti, deer mice. Adrenal, brain and liver masses were similar between color morphs; heart mass was greater in agouti males; and kidney, spleen and testis masses were all significantly greater for non-agouti deer mice. Splenomegaly in non-agouti deer mice was prominent, as spleens of non-agouti deer mice were 50% larger than those of agouti animals. Sex differences varied across organs and color morphs. For both color morphs, males had heavier adrenals and brains, whereas females had heavier livers and spleens. Kidney and heart mass was greater for female non-agouti deer mice, but for agouti animals, heart mass was greater in males and kidney mass differed little between the sexes. For both color morphs, testes and spleen mass was altered by photoperiod in 72 deer mice housed under short- or long-day conditions and the effect was stronger in non-agouti animals. This is the first report of splenomegaly and sex-specific body mass differences associated with the non-agouti allele.

Local Distribution and Coexistence of two Species of Peromyscus in Vermont

In New England, the woodland deer mouse (Peromyscus maniculatus gracilis) and whitelooted mouse (P. leucopus noveboracensis) are forest-dwelling species that may be found on the same site. Choate (1975) reported that P. maniculatus preferred habitats associated with coniferous forests or northern hardwoods and that P. leucopus was found in slightly more xeric habitats dominated by white pine (Pinus strobus), hemlock (Tsuga canadensis), and oaks (Quercus spp.), with populations occasionally extending into adjacent, more mesic northern hardwood forests. Several other authors also have reported that P. maniculatus is found in moist, cool, or coniferous habitats and that P. leucopus is found in dry, warm, or deciduous sites (Klein, 1960; Smith and Speller, 1970; Wrigley, 1969), although Lovejoy (1970) found P. maniculatus generally using dry habitats in the absence of P. leucopus. Sympatric species coexisting in a stable environment may select different foods, differ in temporal or spatial activity, and/or utilize different habitats, thus presumably reducing competition for niches. Hamilton (1941) noted no differences in food habits of P. mantculatus and P. leucopus. Temporal activity has been found to differ between these species in response to weather parameters (Drickamer and Capone, 1977), but neither seasonal nor circadian differences have been reported in New England. Both species are semi-arboreal and may partition niches spatially, but results of studies of arboreal habits of Peromyscus species do not permit a conclusion for P.m. gracilis and P. 1. noveboracensis (see Tadlock and Klein, 1979; Stahl, 1980; Wolff and Hurlbutt, 1982). Peromyscus maniculatus and P. leucopus appear to occupy similar ecological niches in the Northeast (Klein, 1960; Smith and Speller, 1970). The association of microhabitat structure with the distribution of rodents has received increasing attention in recent years (e.g., Carey et al., 1980; Dueser and Shugart, 1978; Holbrook, 1978; M'Closkey, 1976; M'Closkey and Fieldwick, 1975). Discriminant function analysis (DFA) has been used commonly in small mammal studies to describe microhabitats, demonstrate niche separation, or explain coexistence of sympatric species (Cavallaro et al., 1981). Our study was designed to determine how the distribution of coexisting Peromyscus species is related to microhabitat components of a northern hardwoods forest in southern Vermont. METHODS This study was conducted in a northern hardwoods forest in the Grafton Forest Resources Project area, Grafton, Vermont (45'10'N, in the eastern foothills of the 'Green Mountains. Elevations ranged from 250 to 400 m. Sherman live traps (7.6 by 8.9 by 22.9 cm) were set from 21 May through 20 August 1980 on 88, 0.08-ha plots for a total of 6,600 trap nights. Traps were set 15 through 19 July 1981 on 20 new plots, for 500 trap nights. To sample systematically, each plot contained five live traps, one at plot center and the others equidistant from plot corners and center, along diagonals of the plot (Fig. 1) Plots were at least 100 m apart to reduce the frequency of capturing an individual on adjacent plots. By using many plots widely dispersed throughout the study area, we incorporated much of the variability of forest types and structure. If a standard trap grid (e.g., traps spaced 10-15 m) had been used, the capture of an individual at an adjacent grid location would have been less independent of previous captures. The

Small Mammals of a Mine Waste Situation in the Central Adirondacks, New York: A Case of Opportunism by Peromyscus maniculatus

Small mammals were liveand snap-trapped on poorly vegetated granitic mine wastes and in surrounding natural habitats in the central Adirondack Mountains, Essex Co., New York. The small mammal fauna on the mine wastes (seven species) was depauperate compared to that of the surrounding mixed hardwood forests (13 species). Only the woodland deer mouse, Peromyscus maniculatus gracilis (LeConte), was abundant on mine waste, comprising 83% of the small mammals captured. This constituted an atypical habitat for P. m. gracilis. The absence of other species was attributed to the lack of herbaceous cover or to inability to withstand the extremes of moisture or temperature. INTRODUCTION The pattern and extent of mammalian exploitation of a disturbed environment may be a measure of the ecological tolerance and niche plasticity of potential invaders from surrounding environments. The significance of a successful invasion by any species, will depend upon the degree to which the new environment differs from surrounding natural areas and the age of the novel environment. Research was conducted on small mammal colonization of an extensive, sparsely vegetated mine-waste habitat in the Adirondack Mountains of New York. Data were collected on the abundance, sex and age composition, distribution and movements of small mammals on the mine wastes. These data were compared with similar data collected on the small mammals inhabiting nearby natural areas. SITE The research was conducted at the MacIntyre Development of N.L. Industries, Inc., Tahawus, Essex Co. (Santanoni Quadrangle), N.Y. For the past 30 years, N.L. Industries, Inc. (formerly National Lead Company), has conducted open-pit mining operations at Tahawus for ilmenite (titanium) and magnetite (iron) ores. Overburden and waste rock from two mine pits have been deposited in a series of terraced disposal areas which now cover approximately 400 acres. These sites exhibit slow rates of ecological succession, contrasting markedly with the surrounding mixed deciduous forests. Trapping was conducted on waste areas ranging in age from 1-20 years, particularly those of 1215 years. Vegetation is a mosaic of clumps of young hardwoods, herbaceous vegetation and bare rock. Dominant trees are quaking aspen, Populus tremuloides, fire cherry, Prunus pensylvanicus, and white birch, Betula papyrifera. Trees are clumped on sites having sufficient soil to support

Effects of social interaction on eating and drinking in two subspecies of deermice, Peromyscus maniculatus bairdii and Peromyscus maniculatus gracilis

Pair combinations of Peromyscus maniculatus bairdii and Peromyscus maniculatus gracilis were given access to solid food and water or 8 per cent sucrose. All groups consumed more total calories under separate housing conditions than when the pair was housed together. No differences were found among the three cominations of subspecies, and cage size was not a significant variable. These results suggested testing Zajonc's theory of social facilitation, which states that the intensity of the most salient response increases in the presence of conspecifics at the expense of less probable responses. In the second experiment drinking was made the most salinet behaviour by placing the mice under 23-hr liquid deprivation. Contrary to theoretical predictions social inhibition was again demonstrated.

A ten-year study of louse populations on deer mice.

From 1952 to 1961 over 2800 specimens of Peromyscus maniculatus gracilis (Le Conte) were collected in northern Minnesota. Of these 2452 were suitable for the study of louse populations. The host population density varied considerably from year to year with the density being over 5× as large during the peak year as during the low years. Only the louse Hoplopleura hesperomydis was found. The infestation rates varied from 17.5 to 58.0% with an overall rate of 33.8% on the ♂, and from 12.3 to 48.4% with an overall rate of 26.9% on the ♀ hosts. There was no demonstrable relationship between the rate of infestation and the density of the host population. There was a positive relationship between the infestation rates from ♂ and ♀ hosts over the several years. There was no significant change in infestation rate with age of the ♀ host but they did increase with the age of the ♂ host. The infestation rates were similar on the young ♂ and ♀ hosts but were significantly higher on the old ♂♂ than on the old ♀♀. The average infestation on infested ♀ hosts was 19.8 but varied from 1 to 1261. The median population size was 5. On the ♂ hosts the average was 16.2 with extremes of from 1 to 758. The median population size was 6. There was no correlation between infestation size and infestation rate. The average population sizes on ♂ and ♀ hosts showed positive correlation for the years studied. The louse population on the ♀ hosts was composed of 31.5% adults of which 41.8% were ♂♂. The immature portion of the population was composed of 73.9% 1st, 19.1% 2nd, and 6.9% 3rd instars. On the ♂ hosts the population was composed of 46.6% adults of which 40.8 are ♂♂. The immature portion of the population was composed of 69.6% 1st, 19.7% 2nd and 10.7% 3rd instars. The immature-to-adult ♀ ratio was 2.74 on the ♀ and 1.94 on the ♂ hosts. The immature-adult ♀ ratio varied positively with the louse population size. The factors which cause variation in infestation rate and population structure of the lice are apparently different from those which affect the host population.

Small-Mammal Distributions Across the Prairie-Forest Transition of Minnesota and North Dakota

Thirteen taxa of small mammals were collected in the continuous forest, aspen groves, riparian woodland and prairie areas of the prairie-forest transition. Mammals captured were placed in three groups on the basis of habitat selection. Of the forest species, Peromyscus maniculatus gracilis was the most restricted and occurred only in or near conifer forest. P. leucopus noveboracensis was found in coniferous, deciduous and river-bottom forests and in large aspen groves. Clethrionomys gap peri had a similar distribution, but was also found in some small aspen groves with grassy ground cover. Tamias striatus was collected in the continuous forest and nearby large groves. Eutamias minimus and Synaptomys cooperi were collected only in the continuous forest. The prairie species, P. m. bairdii, Onychomys leucogaster and Microtus pennsylvanicus, were found essentially in grassland situations. P. m. bairdii also occurs in aspen groves and river-bottom forests where P. 1. noveboracensis is absent. M. pennsylvanicus appears to be a permanent resident in young groves with a grassy undercover. The nonselective species, Sorex cinereus, Blarina brevicauda and Zapus hudsonius, were found throughout the area in all habitats trapped. Sorex arcticus may also be present in moister habitats throughout the transition. The small-mammal fauna of the prairie-forest ecotone includes fragments of both prairie and forest faunas and reflects the state of flux in the plant associations.