White-footed Mouse Populations Research Articles

Age-Related Decline in Reproductive Sensitivity to Inhibition by Short Photoperiod inPeromyscus Leucopus

Seasonal environments favor the timing of reproduction to match seasons when successful reproduction is most likely. Most species of temperate zone mammals suppress reproduction in winter using changes in day length as a cue. In many species, individuals vary genetically in how strongly they respond to these seasonal cues. Individuals also may modify their response to day length depending upon other factors, including their age. Agespecific changes might occur because young, peripubertal rodents are more strongly affected by harsh conditions than adults, and therefore might be more sensitive to inhibitory photoperiods. We tested the hypothesis that genetic variation in responses to photoperiod persists as individuals age. Young males from a captive population of whitefooted mice (Peromyscus leucopus) that is genetically variable for reproductive inhibition by short day length (SD) were tested for photoperiod responses. Mice were placed in SD within 3 days after birth, tested at age 70 days, allowed to mature for at least 18 weeks at long day length, and then tested again as adults aged� 34 weeks. Young males were more likely to be strongly reproductively suppressed by SD than adults, indicating that age-specific changes in reproductive strategy occur in this population. However, males that were reproductively photoresponsive when young also were more likely to be reproductively photoresponsive as adults. Thus, genetic tendency for reproductive sensitivity to photoperiod is a trait retained from puberty to adulthood, but attenuates with age.

Effects of habitat loss on populations of white-footed mice: testing matrix model predictions with landscape-scale perturbation experiments

Habitat loss is the leading cause of decline in wildlife diversity and abundance throughout the world, but its effects on wildlife are not always predictable. Matrix population modeling is an increasingly common tool used to predict the effects of habitat loss. In spite of the growing number of studies using this approach, and its wide use in conservation practice, the predictions generated by matrix population models are rarely explicitly tested in the field. We compared the ability of a suite of spatially explicit demographic matrix models to predict the response of white-footed mice to loss of high quality habitat at mosaic sites in northeast Connecticut, USA. We tested short-term model predictions with landscape scale habitat perturbation experiments, including clear-cut logging or prescribed burning of high quality habitat at two study sites. Comparison of each model’s predictions with the observed responses at both sites qualitatively supported predictions that perturbation of high quality habitat would have negative effects extending into the surrounding landscape. The best-supported model assumed that evicted residents of the perturbed habitat would successfully resettle in nearby intact habitats, and allowed for gradual population recovery in the perturbed habitat. Similarly, long-term simulations (20 years) revealed how loss of a single habitat could trigger population declines throughout a mosaic site. This study shows that careful consideration of model assumptions such as those pertaining to resettlement behavior is crucial if predictions are to be reliable, and highlights the role of experiments for comparing alternative model predictions.

Projected effects of climate change on tick phenology and fitness of pathogens transmitted by the North American tick Ixodes scapularis

Ixodes scapularis is the principal tick vector of the Lyme borreliosis agent Borrelia burgdorferi and other tick-borne zoonoses in northeastern North America. The degree of seasonal synchrony of nymphal and larval ticks may be important in influencing the basic reproductive number of the pathogens transmitted by I. scapularis. Because the seasonal phenology of tick vectors is partly controlled by ambient temperature, climate and climate change could shape the population biology of tick-borne pathogens. We used projected monthly normal temperatures, obtained from the second version of the Canadian Coupled Global Climate Model (CGCM2) under emissions scenario A2 of the Intergovernmental Panel on Climate Change for a site in southern Ontario, Canada, to simulate the phenology of I. scapularis in a mathematical model. The simulated seasonal abundance of ticks then determined transmission of three candidate pathogens amongst a population of white-footed mice (Peromyscus leucopus) using a susceptible–infected–recovered (SIR) model. Fitness of the different pathogens, in terms of resilience to changes in tick and rodent mortality, minima for infection duration, transmission efficiency and particularly any additional mortality of rodents specifically associated with infection, varied according to the seasonal pattern of immature tick activity, which was different under the temperature conditions projected for the 2020s, 2050s and 2080s. In each case, pathogens that were long-lived, highly transmissible and had little impact on rodent mortality rates were the fittest. However, under the seasonal tick activity patterns projected for the 2020s and 2050s, the fitness of pathogens that are shorter-lived, less efficiently transmitted, and more pathogenic to their natural hosts, increased. Therefore, climate change may affect the frequency and distribution of I. scapularis-borne pathogens and alter their evolutionary trajectories.

Heavy metal exposure, reproductive activity, and demographic patterns in white-footed mice ( Peromyscus leucopus) inhabiting a contaminated floodplain wetland

We examined the concentrations of selected metals and selenium (Se) in the tissues of white-footed mice ( Peromyscus leucopus) collected at a constructed wetland originally created as a retention basin for sediments dredged from Lake DePue, Illinois. These sediments were contaminated with high concentrations of cadmium (Cd), zinc (Zn), and other elements as a result of nearby smelting operations. White-footed mice inhabiting the former retention basin experienced greater exposure to Cd, Pb, and Se than those from nearby reference sites. Concentrations of Cu and Zn in livers of mice from the contaminated wetland and adjacent floodplain reference site were greater than in mice from the more-distant reference sites. Judging by concentrations in their kidneys, white-footed mice inhabiting the floodplain adjacent to the contaminated wetland had greater exposure to Cd than those from the two more-distant reference sites. Concentrations of Hg in tissues of mice did not vary appreciably among sites. Concentrations of Cd and Se in the tissues of some white-footed mice from the contaminated wetland exceeded critical concentrations observed in experimental studies of laboratory mice and rats; with few exceptions tissue Pb concentrations were below published effects levels. However, we did not detect changes in abundance, demographics, or reproductive activity that might suggest population-level effects of contaminant exposure. Mean weight of embryos expressed as a function of crown–rump length did not differ among locations sampled, and no gross lesions indicative of exposure to heavy metals were observed. Kidney and liver weight, corrected for body weight, were nominally, though not significantly, lowest in both male and female mice from areas of increased Cd and Pb exposure. Metals dredged from Lake DePue were still bioavailable 25 years after deposition. However, small mammal populations are resilient to environmental stressors and we did not detect differences in population parameters suggesting that the population of white-footed mice inhabiting the contaminated wetland was at risk from increased exposure to these contaminants.

Number of Immunoreactive GnRH‐Containing Neurons Is Heritable in a Wild‐Derived Population of White‐Footed Mice (Peromyscus leucopus)

The evolution of mammalian brain function depends in part on levels of natural, heritable variation in numbers, location, and function of neurons. However, the nature and amount of natural genetic variation in neural traits and their physiological link to variation in function or evolutionary change are unknown. We estimated the level of within-population heritable variation in the number of gonadotropin-releasing hormone (GnRH) neurons, which play a major role in reproductive regulation, in an unselected outbred population recently derived (<10 generations) from a single natural population of white-footed mice (Peromyscus leucopus, Rafinesque). Young adult male mice exhibited an approximately threefold variation in the number of neurons immunoreactive for GnRH in the brain areas surveyed, as detected using SMI-41 antibody with a single-label avidin-biotin complex method. Consistent with earlier findings of selectable variation in GnRH neurons in this population, the level of genetic variation in this neuronal trait within this single population was high, with broadsense heritability using full-sib analysis estimated at 0.72 (P<0.05). Either weak selection on this trait or environmental variation that results in inconsistent selection on this trait might allow a high level of variation in this population.

Stress and parasitism of white-footed mice (Peromyscus leucopus) in dry and floodplain environments

We hypothesized that flooding represents an environmental stressor that might affect the corticosterone levels, parasite prevalence, and life history of small mammals living in floodplain environments. We compared populations of white-footed mice ( Peromyscus leucopus (Rafinesque, 1818)) on floodplains and dry areas. We found more males on floodplains (p = 0.008) and more females on dry areas (p = 0.005). There were no differences in mass (p &gt; 0.05) or intestinal parasite prevalence (p = 0.665) between dry and floodplain habitats, but bot fly larvae were significantly more prevalent in males living on floodplains (p = 0.043). Floodplain animals had significantly higher levels of corticosterone than dry-area animals in fall, and lower levels in summer (F[1,20] = 4.483, p = 0.047). In addition, we found that animals with intestinal parasites had higher levels of corticosterone than those that were without parasites (p = 0.014) or that harbored bot fly larvae (p = 0.001). Floodplains seem to be harsher environments than dry areas, but this may be a result of differences in habitat rather than a direct result of flooding.

Response of white-footed mice ( Peromyscus leucopus) to fire and fire surrogate fuel reduction treatments in a southern Appalachian hardwood forest

An experiment conducted as part of the multidisciplinary National Fire and Fire Surrogate Study was designed to determine effects of three fuel reduction techniques on small mammals and habitat structure in the southern Appalachian mountains. Four experimental units, each >14-ha were contained within each of three replicate blocks at the Green River Game Land, Polk County, NC. Treatments were (1) prescribed burning (B); (2) mechanical felling of shrubs and small trees (M); (3) mechanical felling + burning (MB); (4) controls (C). Mechanical understory felling treatments were conducted in winter 2001–2002, and prescribed burning was conducted in March 2003. After treatment, there were fewer live trees, more snags, and greater canopy openness in MB than in other treatments. Leaf litter depth was reduced by burning in both B and MB treatments, and tall shrub cover was reduced in all fuel reduction treatments compared to C. Coarse woody debris pieces and percent cover were similar among treatments and controls. We captured 990 individuals of eight rodent species a total of 2823 times. Because white-footed mice composed >79% of all captures, we focused on this species. Populations in experimental units increased 228% on average between 2001 and 2002, but there was no evidence of an effect of the mechanical treatment. From 2002 to 2003, all units again showed an average increase in relative population size, but increases were greater in MB than in the other treatments. Age structure and male to female ratio were not affected by the fuel reduction treatment. Average adult body weight declined from 2001 to 2002, but less so in M than in units that remained C in both years. The proportion of mice captured near coarse woody debris was similar to the proportion captured in open areas for all treatments, indicating that white-footed mice did not use coarse woody debris preferentially or change their use patterns in response to fuel reduction treatments. Land managers should understand possible effects of different fuel reduction treatments on white-footed mouse populations, as they are an important component of the fauna and food chain of deciduous southern Appalachian forests.

SYSTEMATICS OF THE WHITE-FOOTED MOUSE (PEROMYSCUS LEUCOPUS) IN THE MID-ATLANTIC REGION

Since the description of Peromyscus leucopus easti Paradiso, 1960, scant work has been directed toward examining the evolutionary relationships of P. leucopus in the mid-Atlantic region. We used morphometric and molecular analyses to examine the phylogenetic relationships of 3 subspecies known from the eastern United States (P. l. easti, P. l. leucopus, and P. l. noveboracensis); additional specimens from North and South Dakota (P. l. aridulus) were incorporated in the molecular analysis. Morphometric analyses revealed that large mice are found in New England and the Appalachian Mountains as far south as west-central North Carolina and that intermediate-sized mice inhabit the Cumberland Plateau and the lowlands from Virginia southward at least to Alabama. These groups represent P. l. noveboracensis and P. l. leucopus, respectively. The smallest specimens, which are referable to P. l. easti, were found in the vicinity of Princess Anne County, Virginia. The largest mice were found on the southern half of Hatteras Island, North Carolina. Examination of D-loop sequence data revealed that there is no apparent restriction of gene flow among P. leucopus on the mainland of the eastern United States, including those from Princess Anne County, Virginia. However, mice from the southern end of Hatteras Island, North Carolina, were as distinct from specimens from the eastern United States as were mice from North and South Dakota. The population of white-footed mice from Hatteras Island, North Carolina, represents an undescribed subspecies.

The Effects of Forest Fragmentation on Densities of White-footed Mice (Peromyscus leucopus) During the Winter

Abstract Forest fragmentation can influence abiotic and biotic factors important for the reproduction and survival of animals. Previous investigations suggest that, in the fall, more food is available for white-footed mice (Peromyscus leucopus) in edge than interior habitats and in small than large forest fragments. However, in the winter, individuals in small fragments and edge habitat may be more exposed to harsh weather extremes, which can result in higher mortality. We examined the effects of fragment size (small and large) and habitat (edge and interior) on populations of white-footed mice during nest box censuses in the winter (January–April) of 2003 in southwestern Ohio. While population density was initially higher in small than large fragments and edge than interior habitats, by the end of the winter there were no significant differences in population size. Populations in small fragments and edge habitat had larger decreases and greater rates of decline in density than those in large fragments an...

MATERNAL AGE DRIVES SEASONAL VARIATION IN LITTER SIZE OF PEROMYSCUS LEUCOPUS

We examined the effects of maternal age and parity on litter size in 2 populations of white-footed mice (Peromyscus leucopus) in southwestern Ontario, Canada, to determine whether these factors cause seasonal variation in litter size. Litter size increased from 1st to subsequent litters among females that bred for the 1st time in their natal year, but not among females that 1st bred as overwintered adults. Thus, prior reproductive experience was not an important determinant of litter size. Maternal age accounted for approximately 70% of the variance in litter size; mean litter size was greatest among females between 150 and 250 days of age at parturition. Date of birth explained 79% of the variation in mean litter size, with litters born in summer significantly smaller than those born in spring or autumn. This effect was attributed to the fact that most summer litters were produced by primiparous young-of-the-year females. Although litter size declined among old, multiparous females, few individuals survived to the age at which reproductive senescence was apparent. Thus, reproductive senescence plays a minor role in population-wide variation in litter size.

Microhabitat selection of Peromyscus leucopus and P. maniculatus in mid-successional vegetation

Abstract We studied syntopic populations of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus) in mid-successional vegetation to determine microhabitat selections on experimental plots in northeastern Kansas. Microhabitat selections, based on woody stem densities (WSD), differed between species and differed from expected for both species. Peromyscus leucopus used habitats with medium and high WDS more than expected, whereas P. maniculatus used habitats with low WSD more than expected. Our results indicate that as plant succession proceeds on experimental plots, habitats preferred by P. leucopus should increase, whereas habitats preferred by P. maniculatus should decrease.

Early Summer Reproductive Hiatus in Wild Adult White-Footed Mice

An early summer breeding hiatus in wild populations of white-footed mice ( Peromyscus leucopus noveboracensis ) in eastern Virginia has been well documented. This report explores the question of the age of the reproductively inhibited animals and demonstrates that mice reproductively suppressed during the hiatus period were not merely young-of-the-year who had not reached sexual maturity but were adults, many of which were known to be reproductive before the hiatus period. Further, animals known to be adults for an average of >2 months when necropsied during the hiatus period had significantly smaller testes, seminal vesicles, and ovaries than adults with similar histories, captured, and necropsied during other reproductive periods of the year.

Differences in hypothalamic 2-[ [formula omitted]]iodomelatonin binding in photoresponsive and non-photoresponsive white-footed mice, Peromyscus leucopus

Photoperiod is an environmental cue used by many temperate-zone species to regulate their reproductive timing. Within species, the degree of reproductive photoresponsiveness can vary widely both among and within populations. The neuroendocrine mechanisms causing this individual variation in photoresponsiveness are unknown. Using selected lines from a population of white-footed mice known to vary genetically in reproductive photoresponsiveness, we tested the hypothesis that variation in the number and/or location of melatonin receptors is the basis for individual differences in reproductive photoresponsiveness. The brains and pars tuberalis of the pituitary from sixteen mice, (eight mice from each of two lines selected for two generations to respond strongly or weakly to photoperiod), were processed for autoradiography using the radioligand 2-[ 125 I ]-iodomelatonin (IMEL). We found significantly higher specific IMEL binding in the medial preoptic area and the bed nucleus of the stria terminalis of non-responsive mice than responsive mice. There were no differences between groups in specific IMEL binding in the suprachiasmatic and dorsomedial nuclei of the hypothalamus, pars tuberalis, or paraventricular nucleus of the thalamus. These results provide support for the hypothesis that individual variation in photoresponsiveness is due in part to differences in the density or affinity of melatonin receptors.

Effects of Forest Fragmentation on Population Attributes of White-Footed Mice and Eastern Chipmunks

We examined differences between populations of white-footed mice ( Peromyscus leucopus ) and eastern chipmunks ( Tamias striatus ) in woodlot fragments and unfragmented forests and attempted to discriminate among potential causal mechanisms. White-footed mice showed increased population density and body mass in woodlots but otherwise no differences in population attributes between woodlots and forests. Eastern chipmunks showed decreased survival rates in woodlots but no other differences in population parameters between woodlots and forests. Mast production was variable among sites but showed no differences between woodlot and forest sites. Likewise, total biomass of mammalian granivores was similar between woodlot and forest sites, but woodlots contained an impoverished community of granivores. White-footed mice and eastern chipmunks may be affected differentially by forest fragmentation, presumably due to differences in their life-history stategies. Our results suggest that white-footed mice thrive in woodlot fragments due to increased mast availability resulting from decreased biomass of competing granivores. In contrast, eastern chipmunks may be influenced negatively by forest fragmentation, possibly because they are more susceptible to increased rates of predation occurring in woodlots than white-footed mice.

Water-deprived white-footed mice express c- fos on a day/night cycle graded according to the duration of deprivation

Mammals respond to electrolyte and water imbalance by a variety of neural and endocrine mechanisms that regulate water and salt intake and loss. We used the expression of c- fos and Fos-related antigens to indicate neuronal activation in hypothalamic neurons of members of an outbred laboratory population of white-footed mice ( Peromyscus leucopus) deprived of water for biologically reasonable periods of time (6–18 h). We examined Fos-like immunoreactivity (Fos-LIR) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). During the dark period, when these animals are normally active, 6 h of water deprivation produced near-maximal increases in the number of cells positive for Fos-LIR in the SON and PVN. In contrast, during the light period, when these mice are normally inactive and do not have access to water, 6 h of water deprivation only slightly affected Fos-LIR. During the day, it required as much as 12 h of water deprivation to produce increases in Fos-LIR cells approaching those achieved at night. Plasma osmolarity was directly related to the number of Fos-LIR cells. In addition, mice lost weight more rapidly at night than during the day when water-deprived, and also recovered that lost weight more rapidly when access to water was returned. Our results show (1) that biologically reasonable levels of water restriction (and resulting changes in blood osmolarity) induce changes in Fos-LIR in this wild mouse species, and (2) that these mice have a daily cycle of sensitivity to water deprivation that is demonstrated by both behavioral, psychological and immunohistological assessment of reactions to water deprivation.

Demography and Condition of Populations of White-Footed Mice (Peromyscus leucopus) in Late and Early Successional Habitats

Populations of white-footed mice ( Peromyscus leucopus ) were monitored for 3 years (1986–1988) in late and early successional habitats. Late-successional habitats consisted of mature hardwood forests with little herbaceous vegetation. Early successional habitats were induced by treatment with either triclopyr or tebuthiuron herbicides, used with and without annual prescribed burning, and consisted of varying levels of shrubs and herbaceous vegetation. Abundance of white-footed mice was highest in 1986 and declined through 1987 and 1988, which corresponded to declines in biomass of forbs. Abundance was higher on both herbicide treatments than controls and higher on triclopyr than tebuthiuron treatments. Triclopyr-altered habitats provided a mixture of dense shrubs and forbs not found in te-buthiuron-altered sites. Litter size, but not reproductive activity, was higher on triclopyr compared to tebuthiuron treatments in spring 1986. Body condition of adult mice, but not body mass, was higher on herbicide and burned treatments than on controls and unburned treatments, respectively.

Effect of forest patch area on population attributes of white-footed mice (Peromyscus leucopus) in fragmented landscapes

We studied population densities, sex ratios, adult masses, reproductive activity, age structure, and over-summer recapture rates of white-footed mice (Peromyscus leucopus) in 15 woodlots of various sizes and three continuous-forest sites to ascertain the effects of forest patch area on these population attributes. Our study was conducted in west-central Indiana during spring 1992 and 1993 and autumn 1992. Densities of white-footed mice were inversely related to forested area. A survey of previous studies conducted at similar latitudes revealed a similar pattern. Extremely high densities (up to 200 adults/ha) were found in small woodlots (&lt; 0.5 ha). Mass of adult male mice also was inversely related to forest area, and a positive relationship between proportion of adult male mice and forest area was suggested. Ratios of juveniles to adults were positively related to forest area in autumn but not in spring. The proportion of sexually active individuals in the population was not related to forest area, nor were over-summer recapture rates. Our findings indicate that patch area can have dramatic effects on the structure and dynamics of populations of white-footed mice inhabiting fragmented landscapes.

Effects of dimilin® application on white‐footed mouse populations in a central appalachian forest

AbstractDensities, food habits, and physical condition of white‐footed mice (Peromyscus leucopus) were examined on 10 Dimilinr̀‐treated and 10 untreated areas in 1985 and 1986. Estimates of mouse density did not differ significantly (p &gt; 0.05) between treated and untreated areas. However, juvenile/adult female ratios on untreated areas were significantly higher (p &lt; 0.05) than those on treated areas. Mice on treated areas consumed less lepidopteran prey than did mice on untreated areas (p &lt; 0.05), but the total amount of food consumed per mouse did not differ significantly between treated and untreated areas (p &gt; 0.05); mice in treated areas apparently compensated for the loss of lepidopterans by using other food sources more heavily. Body measurements, weight, and fat content of mice did not differ (p &gt; 0.05) between treated and untreated areas.

Studies of Natural Populations of White-Footed Mice: Reduction of Reproduction at Varying Densities

A population of white-footed mice ( Peromyscus leucopus noveboracensis ) on an 11-ha area was studied monthly during 1983–1989 with 600 live-traps and with 254 wooden nest boxes attached to trees. I hypothesized that regulation of population growth would occur each year in the same area at markedly different numerical levels and that the characteristics of reproductive curtailment would be similar between animals in populations of widely different densities. More than 90% of the population known to be alive were captured each month; <20% of suckling young recorded in nest boxes subsequently were captured in traps. The number of adults in the population varied from 22.9/ha in March 1983 to 0.3/ha in November 1984. Significantly more adult males (56.7%) than adult females (43.3%) were captured during the study and a smaller percentage of males than females was reproductively mature in 58 of 72 monthly comparisons. A yearly bimodal curve of reproduction was noted over 7 years with significantly lower proportions of males and females in reproductive condition during May, June, and July than during February–April and August–October. Correlation coefficients between the number of adults of each sex and the percentage in reproductive condition from April 1984 through November 1989 were negative for females at P ≤ 0.01 and for males at P ≤ 0.1. Yearly correlations between the same measurements generally were negative for both sexes, but at widely different densities. No consistent pattern of change in body weight in males and nonpregnant females was noted. Weights of testes, seminal vesicles, ovaries, and uteri generally were significantly smaller in May, June, and July than in March, April, August, September, and October. Factors producing this significant retardation of reproduction at widely different density levels are unknown and are not related to density per se.

Paternal Behavior in a Natural Population of White-footed Mice (Peromyscus leucopus)

-Studies demonstrating paternal care in Peromyscus leucopus are conflicting; laboratory evidence suggests that males care for young at an early age, whereas evidence from small enclosures suggests that paternal care does not exist. This study demonstrates the association of fathers with their weaned young in a wild population of P. leucopus. Live trapping, nest boxes, radio telemetry and DNA fingerprinting were used to determine if and when males associate with their own young. We frequently observed adult males alone with juveniles of either sex after they were weaned. Paternity was likely in most cases, and was confirmed by DNA fingerprinting in some cases. We observed an adult male forage with >two young on two occasions. We did not observe adult females in association with weaned juveniles but often observed them with juveniles before weaning. These findings contradict laboratory studies in small cages and studies in small enclosures which did not observe associations of adult males with young after weaning.