Peromyscus Research Papers - Academia.edu (original) (raw)

Ehrlichia are obligate intracellular bacteria that belong to the family Rickettsiaceae. Human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE) are the 2 ehrlichial diseases that are of greatest health concern in the... more

Ehrlichia are obligate intracellular bacteria that belong to the family Rickettsiaceae. Human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE) are the 2 ehrlichial diseases that are of greatest health concern in the United States. The agents causing HME and HGE are zoonotic pathogens requiring a mammalian reservoir and an arthropod vector. Differences in the geographic distribution of their tick vectors account for the concentration of HME in the South and southeastern United States and HGE in the Northeast and northern Midwest. Both infections have been reported in coastal regions from Rhode Island to Florida. HME and HGE are flulike illnesses that usually are self-limited but may be fatal. Diagnosis is confirmed by identification of the microorganism on blood smear or polymerase chain reaction or by detection of anti-ehrlichial antibody. Doxycycline is the antibiotic of choice for treatment of ehrlichiosis.

We report rapid change of morphology and mitochondrial genes in white-footed mice (Peromyscus leucopus) in the Chicago (Illinois, USA) region. We sequenced mitochondrial DNA COX2 from 55 museum skins of white-footed mice caught in the... more

We report rapid change of morphology and mitochondrial genes in white-footed mice (Peromyscus leucopus) in the Chicago (Illinois, USA) region. We sequenced mitochondrial DNA COX2 from 55 museum skins of white-footed mice caught in the Chicago area since 1855 and from 44 mice recently trapped in the same locations. We found consistent directional genotype replacement at five separate collection locations. We later focused on a single one of these locations (Volo Bog State Natural Area) and sequenced mitochondrial D-loop control region from 58 museum skins of mice collected in 1903-1976 and 32 mice recently trapped there. We found complete and more recent replacement of D-loop haplotypes, apparently occurring between 1976 and 2001. We tested whether these genetic changes were mirrored by changes in morphology by comparing 15 external and cranial traits. We found no significant morphological differences between mice collected in 1903-1976; however, mice collected in 2001-2003 showed 9 of 15 measurements to be significantly changed relative to the earlier samples. Recent mice were longer in total length, with broader, longer noses, and longer but shallower skulls 1 . Discriminant function analysis allowed for 100% correct classification using these traits. Principal components analysis shows variance over time is well distributed across both external and cranial measures. The sequential replacements of haplotypes and the rapid change of morphology can best be explained by replacement of the regional population with immigrants from genetically distinct neighbouring populations, likely facilitated by the large environmental changes occurring over the time period. Replacement with genotypes from external populations may be a common mechanism of evolution of newly adaptive local forms in an increasingly human-impacted world.

h i g h l i g h t s • Stereotypy is time-consuming and effective for assessing severity and drug response. • Chronic, but not sub-chronic treatment with escitalopram attenuates stereotypy. • HS deer mice present with significantly lower... more

h i g h l i g h t s • Stereotypy is time-consuming and effective for assessing severity and drug response. • Chronic, but not sub-chronic treatment with escitalopram attenuates stereotypy. • HS deer mice present with significantly lower striatal SERT density vs. controls.

The karyotype of Peromyscus grandis (Rodentia: Cricetidae)

Elevated glucose levels in the presence of insulin are indicative of type 2 diabetes and the more inclusive metabolic syndrome. Alleles conferring susceptibility to these and other common conditions may be adaptations to past... more

Elevated glucose levels in the presence of insulin are indicative of type 2 diabetes and the more inclusive metabolic syndrome. Alleles conferring susceptibility to these and other common conditions may be adaptations to past environments. It is possible that other mammals exhibiting environmental diversity harbor similar variants; therefore, we assessed glucose regulation in two species of deer mice (Peromyscus), a diverse endemic North American group. The prairie deer mouse, P. maniculatus bairdii (BW), and the Oldfield mouse, P. polionotus subgriseus (PO) differ in sexual dimorphism, behavior and habitat. PO animals exhibit better regulatory ability than BW animals, particularly among males, although both species display equivalent insulin levels/responses and non-fasted glucose levels. Hybrid males exhibit a PO glucose challenge response and subsequent analysis of consomic animals implicates Y chromosome variation as the genetic cause. Two pieces of evidence indicate that the ma...

Background: Recombinant DNA technologies have played a pivotal role in the elucidation of structure-function relationships in hemoglobin (Hb) and other globin proteins. Here we describe the development of a plasmid expression system to... more

Background: Recombinant DNA technologies have played a pivotal role in the elucidation of structure-function relationships in hemoglobin (Hb) and other globin proteins. Here we describe the development of a plasmid expression system to synthesize recombinant Hbs in Escherichia coli, and we describe a protocol for expressing Hbs with low intrinsic solubilities. Since the aand b-chain Hbs of different species span a broad range of solubilities, experimental protocols that have been optimized for expressing recombinant human HbA may often prove unsuitable for the recombinant expression of wildtype and mutant Hbs of other species. Methodology/Principal Findings: As a test case for our expression system, we produced recombinant Hbs of the deer mouse (Peromyscus maniculatus), a species that has been the subject of research on mechanisms of Hb adaptation to hypoxia. By experimentally assessing the combined effects of induction temperature, induction time and E. coli expression strain on the solubility of recombinant deer mouse Hbs, we identified combinations of expression conditions that greatly enhanced the yield of recombinant protein and which also increased the efficiency of post-translational modifications.

Relative to morphological traits, we know little about how genetics influence the evolution of complex behavioural differences in nature 1 . It is unclear how the environment influences natural variation in heritable behaviour 2 , and... more

Relative to morphological traits, we know little about how genetics influence the evolution of complex behavioural differences in nature 1 . It is unclear how the environment influences natural variation in heritable behaviour 2 , and whether complex behavioural differences evolve through few genetic changes, each affecting many aspects of behaviour, or through the accumulation of several genetic changes that, when combined, give rise to behavioural complexity 3 . Here we show that in nature, oldfield mice (Peromyscus polionotus) build complex burrows with long entrance and escape tunnels, and that burrow length is consistent across populations, although burrow depth varies with soil composition. This burrow architecture is in contrast with the small, simple burrows of its sister species, deer mice (P. maniculatus). When investigated under laboratory conditions, both species recapitulate their natural burrowing behaviour. Genetic crosses between the two species reveal that the derived burrows of oldfield mice are dominant and evolved through the addition of multiple genetic changes. In burrows built by first-generation backcross mice, entrancetunnel length and the presence of an escape tunnel can be uncoupled, suggesting that these traits are modular. Quantitative trait locus analysis also indicates that tunnel length segregates as a complex trait, affected by at least three independent genetic regions, whereas the presence of an escape tunnel is associated with only a single locus. Together, these results suggest that complex behaviours-in this case, a classic 'extended phenotype' 4 -can evolve through multiple genetic changes each affecting distinct behaviour modules.

Although post-dispersal seed predators are common and often reduce seed density, their influence on plant population abundance remains unclear. On the one hand, increasing evidence suggests that many plant populations are seed limited,... more

Although post-dispersal seed predators are common and often reduce seed density, their influence on plant population abundance remains unclear. On the one hand, increasing evidence suggests that many plant populations are seed limited, implying that seed predators could reduce plant abundance. On the other hand, it is generally uncertain whether the magnitude of seed limitation imposed by granivores is strong enough to overcome densitydependent processes that could compensate for seed loss at later stages. We examined the impact of seed predation by small mammals, primarily deer mice (Peromyscus maniculatus), on seedling recruitment and subsequent plant establishment of two perennial grassland forbs in western Montana, USA: Lupinus sericeus (Fabaceae) and Lithospermum ruderale (Boraginaceae). The experiment combined graded densities of seed addition for each species with a small-mammal exclusion treatment. Seedling recruitment and plant establishment were monitored in the experimental plots for up to three years. For both species, small-mammal exclusion increased the total number of seedlings that emerged, and these effects were still significant three years after seed addition, resulting in greater numbers of established plants inside exclosures than in control plots. We also found evidence of seed limitation, with increasing density of seeds added leading to increased numbers of seedlings. Results from seed addition and small-mammal exclusion experiments in later years also revealed significant impacts of small mammals on seedling emergence. These results suggest that granivores can have potentially important impacts in limiting forb abundance in grasslands communities.

The Anacapa deer mouse is an endemic subspecies that inhabits Anacapa Island, part of Channel Islands National Park, California. We used mitochondrial DNA cytochrome c oxidase subunit II gene (COII) and 10 microsatellite loci to evaluate... more

The Anacapa deer mouse is an endemic subspecies that inhabits Anacapa Island, part of Channel Islands National Park, California. We used mitochondrial DNA cytochrome c oxidase subunit II gene (COII) and 10 microsatellite loci to evaluate the levels of genetic differentiation and variation in 1400 Anacapa deer mice sampled before and for 4 years after a black rat (Rattus rattus) eradication campaign that included trapping, captive holding and reintroduction of deer mice. Both mitochondrial and microsatellite analyses indicated significant differentiation between Anacapa deer mice and mainland mice, and genetic variability of mainland mice was significantly higher than Anacapa mice even prior to reintroduction. Bayesian cluster analysis and Principal Coordinates Analysis indicated that East, Middle and West Anacapa mice were genetically differentiated from each other, but translocation of mice among islands resulted in the East population becoming less distinct as a result of management. Levels of heterozygosity were similar before and after management. However, numerous private alleles in the founder populations were not observed after reintroduction and shifts in allele frequencies occurred, indicating that the reintroduced populations experienced substantial genetic drift. Surprisingly, two mitochondrial haplotypes observed in an earlier study of Anacapa deer mice were lost in the 20 years prior to the rat eradication program, leaving only a single haplotype in Anacapa deer mice. This study demonstrates how genetic monitoring can help to understand the re-establishment of endemic species after the eradication of invasive species and to evaluate the effectiveness of the management strategies employed.

Members of Haplomylomys, a subgenus of Peromyscus, are widely distributed in northwestern Mexico and the southwestern United States; due to its taxonomic complexity, the systematics and biogeography of this group have been widely studied.... more

Members of Haplomylomys, a subgenus of Peromyscus, are widely distributed in northwestern Mexico and the southwestern United States; due to its taxonomic complexity, the systematics and biogeography of this group have been widely studied. However, the evolutionary relationships between island taxa within the eremicus group remain poorly understood. Our goals were to assess the evolutionary history of Haplomylomys, and to identify geological and climatic events that might have affected its evolutionary history. Phylogenetic relationships were analyzed using 3 mitochondrial gene fragments (Cytb, COI, and COIII) from 61 individuals collected throughout the geographic range of Haplomylomys. Maximum likelihood and Bayesian phylogenetic analyses identified 2 main clades. The 1st includes P. californicus; the 2nd, all the species within the eremicus group divided into 4 clades. Taken together, our phylogenetic analysis and genetic divergence values suggest several taxonomic changes are needed among insular members of the eremicus group. Molecular dating analysis indicates that the phylogeny of Haplomylomys is possibly correlated with the formation of the Colorado River, the latest embayment of the Gulf of California during the Neogene, the trans-peninsular seaway in the central Vizcaino region, and the Last Glacial Maximum; these events may have had an effect at the species and subspecies level for Haplomylomys taxa.

Background Contamination with heavy metals is among the most hazardous environmental concerns caused by mining activity. A valuable tool for monitoring these effects is the use of sentinel organisms. Particularly, small mammals living... more

Background Contamination with heavy metals is among the most hazardous environmental concerns caused by mining activity. A valuable tool for monitoring these effects is the use of sentinel organisms. Particularly, small mammals living inside mine tailings are an excellent study system because their analysis represents a realistic approach of mixtures and concentrations of metal exposure. Purpose We analyzed metal tissue concentrations and DNA damage levels for comparison between genders of a sentinel (Peromyscus melanophrys) and a nonsentinel (Baiomys musculus) species. Also, the relationship between DNA damage and the distance from the contamination source was evaluated. Methods This study was conducted in an abandoned mine tailing at Morelos, Mexico. Thirty-six individuals from both species at the exposed and reference sites were sampled. Metal concentrations in bone and liver of both species were analyzed by atomic absorption spectrophotometry, and DNA damage levels were assayed using the alkaline comet assay. Results In general, concentrations of zinc, nickel, iron, and manganese were statistically higher in exposed individuals. A significant effect of the organ and the site on all metal tissue concentrations was detected. Significant DNA damage levels were registered in the exposed group, being higher in B. musculus. Females registered higher DNA damage levels than males. A negative relationship between distance from the mine tailing and DNA damage in B. musculus was observed. Conclusions We consider that B. musculus is a suitable species to assess environmental quality, especially for bioaccumulable pollutants-such as metals-and recommend that it may be considered as a sentinel species.

Vaccinating wildlife is becoming an increasingly popular method to reduce human disease risks from pathogens such as Borrelia burgdorferi, the causative agent of Lyme disease. To successfully limit human disease risk, vaccines targeting... more

Vaccinating wildlife is becoming an increasingly popular method to reduce human disease risks from pathogens such as Borrelia burgdorferi, the causative agent of Lyme disease. To successfully limit human disease risk, vaccines targeting the wildlife reservoirs of B. burgdorferi must be easily distributable and must effectively reduce pathogen transmission from infected animals, given that many animals in nature will be infected prior to vaccination. We assessed the efficacy of an easily distributable oral bait vaccine based on the immunogenic outer surface protein A (OspA) to protect uninfected mice from infection and to reduce transmission from previously infected white-footed mice, an important reservoir host of B. burgdorferi. Oral vaccination of white-footed mice effectively reduces transmission of B. burgdorferi at both critical stages of the Lyme disease transmission cycle. First, oral vaccination of uninfected white-footed mice elicits an immune response that protects mice from B. burgdorferi infection. Second, oral vaccination of previously infected mice significantly reduces the transmission of B. burgdorferi to feeding ticks despite a statistically nonsignificant immune response. We used the estimates of pathogen transmission to and from vaccinated and unvaccinated mice to model the efficacy of an oral vaccination campaign targeting wild white-footed mice. Projection models suggest that the effects of the vaccine on both critical stages of the transmission cycle of B. burgdorferi act synergistically in a positive feedback loop to reduce the nymphal infection prevalence, and thus human Lyme disease risk, well below what would be expected from either effect alone. This study suggests that oral immunization of wildlife with an OspA-based vaccine can be a promising long-term strategy to reduce human Lyme disease risk.

Culture and the polymerase chain reaction (PCR) were compared for detection of Borrelia burgdorferi infection in wild-caught Peromyscus leucopus and experimentally inoculated C.B-17 scid/scid (severe combined immunodeficient) mice. PCR... more

Culture and the polymerase chain reaction (PCR) were compared for detection of Borrelia burgdorferi infection in wild-caught Peromyscus leucopus and experimentally inoculated C.B-17 scid/scid (severe combined immunodeficient) mice. PCR targeted highly conserved regions of the ospA gene and could detect one to five cultured organisms and 10 to 50 copies of molecularly cloned ospA DNA. Organs (kidney, spleen, and urinary bladder) and/or ear biopsy samples were obtained from 108 captured P. keucopus mice, and tissues were obtained from 7 experimentally inoculated mice. A simple sample-processing procedure with proteinase K and detergent treatment was used in the PCR analysis. Overall, B. burgdorferi was detected in 29 of 108 (27%) P. leucopus mice by culture and in 31 of 108 (29%o) mice by PCR. As assessed by the kappa statistic, agreement between PCR and culture was high for ear and bladder (kappa = 0.80 and 0.65, respectively) and low for kidney and spleen (kappa = 0.37 and 0.03, respectively). While concordant results were obtained from 98

1. Pathogens and immune challenges can induce changes in host phenotype in ways that indirectly impact important community interactions, including those that affect host-pathogen interactions. 2. To explore host behavioural response to... more

1. Pathogens and immune challenges can induce changes in host phenotype in ways that indirectly impact important community interactions, including those that affect host-pathogen interactions. 2. To explore host behavioural response to immune challenge, we exposed wild white-footed mice (Peromyscus leucopus) to an immunogen from an endemic, zoonotic pathogen, the spirochete Borrelia burgdorferi. White-footed mice are a major reservoir host of Lyme disease (LD) spirochetes in northeastern USA and an abundant member of forest communities. The activity patterns, foraging behaviour, and space use of white-footed mice have implications for population growth rates of community members upon which mice incidentally prey (i.e. gypsy moths and native thrushes), as well as potentially determining host-vector encounter rates and human risk of LD. 3. Immunochallenge led to specific humoral (antibody) and cellular (i.e. elevated neutrophils and eosinophils) immune responses, supporting use of the immunogen as a surrogate for pathogenic infection. 4. Immunochallenged mice had reduced wheel-running activity early in the night when measured in the lab. However, mouse activity, as measured by track plates in natural field experiments, did not differ between mice exposed to the immunogen and unexposed mice. 5. Foraging behaviour of wild mice in the field -assessed with giving-up densities of seed at artificial feeding stations -was affected by exposure to the immunogen. Whereas immunochallenge did not influence whether foraging mice gained information on patch quality while foraging, it led to reductions in predator avoidance during foraging, suggesting that the proportion of space used by foraging mice may be greater as a result of immunochallenge. This increased space use is predicted to increase encounter rates with patchily distributed LD vectors (ticks) and with incidental prey items. 6. Thus, immunochallenge in white-footed mice, and potentially pathogenic infection, have the potential to indirectly impact community interactions, including those important for pathogen transmission.

A major challenge to understanding the genetic basis of complex behavioral evolution is the quantification of complex behaviors themselves. Deer mice of the genus Peromyscus vary in their burrowing behavior, which leaves behind a physical... more

A major challenge to understanding the genetic basis of complex behavioral evolution is the quantification of complex behaviors themselves. Deer mice of the genus Peromyscus vary in their burrowing behavior, which leaves behind a physical trace that is easily preserved and measured. Moreover, natural burrowing behaviors are recapitulated in the lab, and there is a strong heritable component. Here we discuss potential mechanisms driving variation in burrows with an emphasis on two sister species: P. manic-ulatus, which digs a simple, short burrow, and P. polionotus, which digs a long burrow with a complex architecture. A forward-genetic cross between these two species identified several genomic regions associated with burrow traits, suggesting this complex behavior has evolved in a modular fashion. Because burrow differences are most likely due to differences in behavioral circuits, Peromyscus burrowing offers an exciting opportunity to link genetic variation between natural populations to evolutionary changes in neural circuits.

The epidemiology of vector-borne zoonotic diseases is determined by encounter rates between vectors and hosts. Alterations to the behavior of reservoir hosts caused by the infectious agent have the potential to dramatically alter disease... more

The epidemiology of vector-borne zoonotic diseases is determined by encounter rates between vectors and hosts. Alterations to the behavior of reservoir hosts caused by the infectious agent have the potential to dramatically alter disease transmission and human risk. We examined the effect of Borrelia burgdorferi, the etiological agent of Lyme disease, on one of its most important reservoir hosts, the white-footed mouse, Peromyscus leucopus. We mimic natural infections in mice using the vector (Black-legged ticks, Ixodes scapularis) and examine the immunological and behavioral responses of mouse hosts. Despite producing antibodies against B. burgdorferi, infected mice did not have elevated white blood cells compared with uninfected mice. In addition, infected and uninfected mice did not differ in their wheel-running activity. Our results suggest that infection with the spirochete B. burgdorferi has little impact on the field activity of white-footed mice. Lyme disease transmission appears to be uncomplicated by pathogen-altered behavior of this reservoir host.

, The Air Development Test Center, Eglin Air Force Base (AFB), Florida, developed, tested, and calibrated the aerial spray systems used in support of Operation RANCH HAND and the US Army Chemical Corps in Vietnam. Twenty major test and... more

, The Air Development Test Center, Eglin Air Force Base (AFB), Florida, developed, tested, and calibrated the aerial spray systems used in support of Operation RANCH HAND and the US Army Chemical Corps in Vietnam. Twenty major test and evaluation projects of aerial spray equipment were conducted on four fully instrumented test grids, each uniquely arrayed to match the needs of fixed-wing, helicopter, or jet aircraft. Each of the grids was established within the boundary of Test Area 52A of the Eglin Reservation. Methods: The tests, conducted under climatic and environmental conditions similar to those in Vietnam, included the use of the military herbicides (Agents) Orange, Purple, White, and Blue. Approximately 75,000 kg of 2,4,5-trichlorophenoxyacetic acid (2,4,5-3") and 76,000 kg of 2,4-dichlorophenoxyacetic acid (2,4-D) were aerially disseminated on an area of less than 3 km z during the period 1962-1970. Data from the analysis of archived samples suggested that an estimated 3.1 kg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), present as a contaminant, were aerially released in the test area. Because most of the vegetation had been removed before establishing the test site in 1961, there was an opportunity to follow ground-based residues independent of canopy interception, and the resulting high solar exposure of initial residues. Studies of the soils, fauna, flora, and aquatic ecosystems of the test grids and associated perimeters of Test Area C-52A (an area totally more than 8 km z) were initiated in 1969 and concluded in 1984. Results and Discussion: Data from soil samples collected from 1974 through 1984 suggested that less than one percent of the TCDD that was present in soil when sampling began persisted through the ten-year period of sampling. More than 340 species of organisms were observed and identified within the test area. More than 300 biological samples were analyzed for TCDD and detectable residues were found in 16 of 45 species examined. Examination of the ecological niches of the species containing TCDD residues suggested each was in close contact with contaminated soil. Indepth field studies, including anatomical, histological and ultrastructural examinations, spanning more than 50 generations of the Beachmouse, Peromyscus polionotus, demonstrated that continual exposure to soil concentrations of 0.1 to 1.5 parts-per-billion (ng/g) of TCDD, had minimal effects upon the health and reproduction of this species. Condusions: Since Agent Orange with its associated TCDD contaminant was aerially disseminated on the test grids, Test Area C-52A provided a 'field laboratory' for what may have happened in Viemam, had there been no intercepting forest cover. However, in Viemam a 'typical' mission would have disseminated 14.8 kg of 2,4,5-T/ha, most of which was intercepted by the forest canopy, versus the 876 kg 2,4,5=T/ha on the test grid at Eglin. Moreover, each hectare on the Eglin test grid received at least 1,300 times more TCDD than a hectare sprayed with Agent Orange in Vietnam. The disappearance or persistence of TCDD is dependent upon how it enters the ecosystem. Spray equipment test and evaluations missions at Eglin were generally scheduled and conducted with environmental conditions that were optimal for spray op= erations. This suggests that conditions favorable for dissemination of herbicide were the same conditions favorable for photodegradation of TCDD. It was likely that 99 percent of the TCDD never persisted beyond the day of application. No long-term adverse ecological effects were documented in these studies despite the massive quantities of herbicides and TCDD that were applied to the site. Reviews by the US Environmental Protection Agency and the National Academy of Sciences' Institute of Medicine did not address the fate of Agent Orange and TCDD as described in these studies from Eglin AFB, Florida.

Although high testosterone (T) levels inhibit paternal behaviour in birds breeding in temperate zones many paternal mammals have a very different breeding biology, characterized by a post-partum oestrus. In species with post-partum... more

Although high testosterone (T) levels inhibit paternal behaviour in birds breeding in temperate zones many paternal mammals have a very different breeding biology, characterized by a post-partum oestrus. In species with post-partum oestrus, males may engage in T-dependent behaviours such as aggression and copulation simultaneously with paternal behaviour. We previously found that T promotes paternal behaviour in the California mouse, Peromyscus californicus. We examine whether this effect is mediated by the conversion of T to oestradiol (E 2 ) by aromatase. In the ® rst experiment, gonadectomized males treated with T or E 2 implants showed higher levels of huddling and pup grooming behaviour than gonadectomized males treated with dihydrotestosterone or empty implants. In the second experiment, we used an aromatase inhibitor (fadrozole) (FAD) to con® rm these results. Gonadectomized males treated with T 1 vehicle or E 2 1 FAD showed higher levels of huddling and pup grooming behaviour than gonadectomized males treated with T 1 FAD or empty implants. Although E 2 is known to promote the onset of maternal behaviour to our knowledge our results are the ® rst to demonstrate that E 2 can promote paternal behaviour in a paternal mammal. These results may explain how mammals express paternal behaviour while T levels are elevated.

The relationship between androgenic hormones, like testosterone (T), and aggression is extensively studied in human populations. Yet, while this work has illuminated a variety of principals regarding the behavioral and phenotypic effects... more

The relationship between androgenic hormones, like testosterone (T), and aggression is extensively studied in human populations. Yet, while this work has illuminated a variety of principals regarding the behavioral and phenotypic effects of T, it is also hindered by inherent limitations of performing research on people. In these instances, animal research can be used to gain further insight into the complex mechanisms by which T influences aggression. Here, we explore recent studies on T and aggression in numerous vertebrate species, although we focus primarily on males and on a New World rodent called the California mouse (Peromyscus californicus). This species is highly territorial and monogamous, resembling the modern human social disposition. We review (i) how baseline and dynamic T levels predict and/or impact aggressive behavior and disposition; (ii) how factors related to social and physical context influence T and aggression; (iii) the reinforcing or "rewarding" as...

Seasonal changes in adaptations associated with winter coping strategies have been frequently studied. Central among the suite of energy-saving, winter-coping strategies is the suspension of reproductive activities. The inhibition of... more

Seasonal changes in adaptations associated with winter coping strategies have been frequently studied. Central among the suite of energy-saving, winter-coping strategies is the suspension of reproductive activities. The inhibition of reproduction by nontropical rodents is mediated by daylength changes. Although balanced annual energy budgets are critical, survival and subsequent reproductive success also require avoiding predators, illness, and early death. Because the stressors of winter could lead to suppressed immune function, we hypothesized that animals should have evolved survival strategies involving immunoenhancement. Short daylengths provide a predictive cue to individuals that could be used to enhance immune function in advance of stress-induced immunosuppression. In Experiment 1, adult female deer mice (Peromyscus maniculatus) were housed in either long (LD 16:8) or short (LD 8:16) days for 8 weeks, then injected with the chemical carcinogen 9,10-dimethyl-1,2benzanthracene (DMBA) dissolved in dimethyl sulfoxide (DMSO) or with the DMSO vehicle alone. Animals were evaluated weekly for 8 weeks after injection. None of the animals treated with DMSO developed tumors in any of the experiments. Nearly 90% of the long-day deer mice injected with DMBA developed squamous cell carcinoma. None of the short-day deer mice injected with DMBA developed tumors. Small lesions developed at the site of injection; short-day females had less severe lesions and healed faster than long-day females. Immunoglobulin G (IgG) response to i.p. injection of sheep red blood cells (SRBC) did not differ between photoperiodic conditions. The role of estrogens in the photoperiodic responses was evaluated in Experiment 2: Ovariectomized or sham-ovariectomized deer mice received estradiol benzoate replacement therapy or a control procedure in long daylengths for 8 weeks prior to injection of DMBA or DMSO, then were monitored for 8 additional weeks. Females treated with DMBA developed tumors at the same rate, regardless of estrogen manipulation. Estrogen did not affect healing rates. In Experiment 3, female deer mice were injected with a slurry of microspheres that either contained bromocriptine or were empty. Suppression of prolactin with bromocryptine resulted in a decrease of tumor incidence from 55.6% to 24% in long-day females 8 weeks after injection with DMBA. Healing rates were not affected by prolactin manipulations. Silastic capsules that were filled with either melatonin or cholesterol were implanted into long-day female deer mice in Experiment 4; 8 weeks later, females received an injection of either DMBA or DMSO, then were monitored for 8 weeks. Approximately 66% of females implanted with cholesterol and injected with DMSO developed histologically verified tumors. None of the melatonin-implanted mice developed tumors. Melatonin did not affect healing rates. Taken together, these results indicate that photoperiod can exert a functionally significant effect on immune processes and clinical disease.

Researchers have documented microhabitat partitioning among the heteromyid rodents of the deserts of North America that may result from microhabitat specific predation rates; large/bipedal species predominate in the open/risky... more

Researchers have documented microhabitat partitioning among the heteromyid rodents of the deserts of North America that may result from microhabitat specific predation rates; large/bipedal species predominate in the open/risky microhabitat and small/quadrupedal species predominate in the bush/safer microhabitat. Here, we provide direct experimental evidence on the role of predatory risk in affecting the foraging behavior of three species of heteromyid rodents: Arizona pocket mouse (Perognathus amplus; small/quadrupedal), Bailey's pocket mouse (P. baileyi; large/quadrupedal), and Merriam's kangaroo rat (Dipodomys merriami; large/bipedal). Both kangaroo rats and pocket mice are behaviorally flexible and able to adjust their foraging behavior to nightly changes in predatory risk. Under low levels of perceived predatory risk the kangaroo rat foraged relatively more in the open microhabitat than the two pocket mouse species. In response to the presence of barn owls, however, all three species shifted their habitat use towards the bush microhabitat. In response to direct measures of predatory risk, i.e. the actual presence of owls, all three species reduced foraging and left resource patches at higher giving up densities of seeds. In response to indirect indicators of predatory risk, i.e. illumination, there was a tendency for all three species to reduce foraging. The differences in morphology between pocket mice and kangaroo rats do appear to influence their behavioral responses to predatory risk.

Dietary shifts are commonly exhibited by omnivorous consumers when foraging from variable food resources. One advantage of dietary shifts for a consumer is the ability to gain complementary resources from different foods. In addition,... more

Dietary shifts are commonly exhibited by omnivorous consumers when foraging from variable food resources. One advantage of dietary shifts for a consumer is the ability to gain complementary resources from different foods. In addition, dietary shifts often affect food-web dynamics. Despite the importance of dietary shifts to organismal, community, and ecosystem ecology, empirical studies of the ecological mechanisms that control dietary shifts are limited in scope. In this study, we tested the effects of complementary resources on dietary shifts of an omnivorous mammal, the white-footed mouse Peromyscus leucopus, in the context of depletable food patches in the natural environment. We used two complementary resources: seeds that provide a higher energy gain per unit handling time and mealworms that provide a higher protein gain per unit handling time. Stable isotopes of carbon and nitrogen (d 13 C, d 15 N) in mouse plasma were used to quantify dietary shifts, and we determined giving-up density (GUD), the food density at which a forager leaves a food patch (for an optimal forager, it should correspond to the quitting harvest rate that balances net fitness gain with various costs of foraging). The results showed that GUD increased most significantly when a mixture of seeds and mealworms was added, compared to when only seeds or mealworms were added. This suggests that, given a similar level of food availability, a patch with a mixture of complementary foods is of higher quality than a patch with only one type of food. Moreover, GUD measured with seeds (GUD s ) correlated positively with seed availability, and GUD measured with mealworms (GUD mw ) correlated positively with mealworm availability, indicating that the marginal value of seeds or mealworms decreases with their relatively availability in the environment. As GUD s increased, P. leucopus shifted their diets toward higher trophic levels, and as GUD mw increased, P. leucopus shifted their diets toward lower trophic levels, suggesting dietary shifts driven by food complementarity. This study demonstrated that the combination of giving-up density and stable-isotope analysis holds great potential for testing ecological mechanisms underlying dietary shifts.

Risk of human exposure to vector-borne zoonotic pathogens is a function of the abundance and infection prevalence of vectors. We assessed the determinants of Lyme-disease risk (density and Borrelia burgdorferi-infection prevalence of... more

Risk of human exposure to vector-borne zoonotic pathogens is a function of the abundance and infection prevalence of vectors. We assessed the determinants of Lyme-disease risk (density and Borrelia burgdorferi-infection prevalence of nymphal Ixodes scapularis ticks) over 13 y on several field plots within eastern deciduous forests in the epicenter of US Lyme disease (Dutchess County, New York). We used a model comparison approach to simultaneously test the importance of ambient growing-season temperature, precipitation, two indices of deer (Odocoileus virginianus) abundance, and densities of white-footed mice (Peromyscus leucopus), eastern chipmunks (Tamias striatus), and acorns (Quercus spp.), in both simple and multiple regression models, in predicting entomological risk. Indices of deer abundance had no predictive power, and precipitation in the current year and temperature in the prior year had only weak effects on entomological risk. The strongest predictors of a current year's risk were the prior year's abundance of mice and chipmunks and abundance of acorns 2 y previously. In no case did inclusion of deer or climate variables improve the predictive power of models based on rodents, acorns, or both. We conclude that interannual variation in entomological risk of exposure to Lyme disease is correlated positively with prior abundance of key hosts for the immature stages of the tick vector and with critical food resources for those hosts. Citation: Ostfeld RS, Canham CD, Oggenfuss K, Winchcombe RJ, Keesing F (2006) Climate, deer, rodents, and acorns as determinants of variation in Lyme-disease risk. PLoS Biol 4(6): e145.

Invasive plants may compete with native plants by increasing the pressure of native consumers, a mechanism known as ''apparent competition.'' Apparent competition can be as strong as or stronger than direct competition, but the role of... more

Invasive plants may compete with native plants by increasing the pressure of native consumers, a mechanism known as ''apparent competition.'' Apparent competition can be as strong as or stronger than direct competition, but the role of apparent competition has rarely been examined in biological invasions. We used four years of demographic data and seed-removal experiments to determine if introduced grasses caused elevated levels of seed consumption on native plant species in a coastal dune system in California, USA. We show that the endangered, coastal dune plant Lupinus tidestromii experiences high levels of predispersal seed consumption by the native rodent Peromyscus maniculatus due to its proximity to the invasive grass, Ammophila arenaria. We use stage-structured, stochastic population models to project that two of three study populations will decline toward extinction under ambient levels of consumption. For one of these declining populations, a relatively small decrease in consumption pressure should allow for persistence. We show that apparent competition with an invasive species significantly decreases the population growth rate and persistence of a native species. We expect that apparent competition is an important mechanism in other ecosystems because invasive plants often change habitat structure and plant-consumer interactions. Possible implications of the apparent-competition mechanism include selective extinction of species preferred by seed consumers in the presence of an invasive species and biological homogenization of communities toward non-preferred native plant species.

Many pathogens, such as the agents of West Nile encephalitis and plague, are maintained in nature by animal reservoirs and transmitted to humans by arthropod vectors. Efforts to reduce disease incidence usually rely on vector control or... more

Many pathogens, such as the agents of West Nile encephalitis and plague, are maintained in nature by animal reservoirs and transmitted to humans by arthropod vectors. Efforts to reduce disease incidence usually rely on vector control or immunization of humans. Lyme disease, for which no human vaccine is currently available, is a commonly reported vector-borne disease in North America and Europe. In a recently developed, ecological approach to disease prevention, we intervened in the natural cycle of the Lyme disease agent (Borrelia burgdorferi) by immunizing wild white-footed mice (Peromyscus leucopus), a reservoir host species, with either a recombinant antigen of the pathogen, outer surface protein A, or a negative control antigen in a repeated field experiment with paired experimental and control grids stratified by site. Outer surface protein A vaccination significantly reduced the prevalence of B. burgdorferi in nymphal blacklegged ticks (Ixodes scapularis) collected at the sites the following year in both experiments. The magnitude of the vaccine's effect at a given site correlated with the tick infection prevalence found on the control grid, which in turn correlated with mouse density. These data, as well as differences in the population structures of B. burgdorferi in sympatric ticks and mice, indicated that nonmouse hosts contributed more to infecting ticks than previously expected. Thus, where nonmouse hosts play a large role in infection dynamics, vaccination should be directed at additional species.

; the cause of this disease is unknown. In this study, the genetic identification and characterization of a novel virus related to human hepatitis E virus (HEV) isolated from bile samples of chickens with HS syndrome is reported. Based... more

; the cause of this disease is unknown. In this study, the genetic identification and characterization of a novel virus related to human hepatitis E virus (HEV) isolated from bile samples of chickens with HS syndrome is reported. Based upon the similar genomic organization and significant sequence identity of this virus with HEV, the virus has been tentatively named avian HEV in order to distinguish it from human and swine HEV. Electron microscopy revealed that avian HEV is a nonenveloped virus particle of 30-35 nm in diameter. The sequence of the 3h half of the viral genome (" 4 kb) was determined. Sequence analyses revealed that this genomic region contains the complete 3h non-coding region, the complete genes from open reading frames (ORFs) 2 and 3, the complete RNA-dependent RNA polymerase (RdRp) gene and a partial helicase gene from ORF 1. The helicase gene is the most conserved gene between avian HEV and other HEV strains, displaying 58-61 % aa and 57-60 % nt sequence identities. The RdRp gene of avian HEV shares 47-50 % aa and 52-53 % nt sequence identities and the putative capsid gene (ORF 2) of avian HEV shares 48-49 % aa and 48-51 % nt sequence identities with the corresponding regions of other known HEV strains. Phylogenetic analysis indicates that avian HEV is genetically related to, but distinct from, other known HEV strains. This discovery has important implications for HEV animal models, nomenclature and natural history. 0001-7760 # 2001 SGM CEEJ Downloaded from www.microbiologyresearch.org by (1999). Serological evidence for swine hepatitis E virus infection in Australian pig herds. Veterinary Microbiology 68, 95-105.

Deer mice (Peromyscus maniculatus) that are native to high altitudes in the Rocky Mountains have evolved hemoglobins with an increased oxygen-binding affinity relative to those of lowland conspecifics. To elucidate the molecular... more

Deer mice (Peromyscus maniculatus) that are native to high altitudes in the Rocky Mountains have evolved hemoglobins with an increased oxygen-binding affinity relative to those of lowland conspecifics. To elucidate the molecular mechanisms responsible for the evolved increase in hemoglobin-oxygen affinity, the crystal structure of the highland hemoglobin variant was solved and compared with the previously reported structure for the lowland variant. Highland hemoglobin yielded at least two crystal types, in which the longest axes were 507 and 230 Å. Using the smaller unit cell crystal, the structure was solved at 2.2 Å resolution. The asymmetric unit contained two tetrameric hemoglobin molecules. The analyses revealed that αPro50 in the highland hemoglobin variant promoted a stable interaction between αHis45 and heme that was not seen in the αHis50 lowland variant. The αPro50 mutation also altered the nature of atomic contacts at the α1β2/α2β1 intersubunit interfaces. These results d...

The deer mouse (genus Peromyscus) is the most abundant mammal in North America, and it occupies almost every type of terrestrial habitat. It is not surprising therefore that the natural history of Peromyscus is among the best studied of... more

The deer mouse (genus Peromyscus) is the most abundant mammal in North America, and it occupies almost every type of terrestrial habitat. It is not surprising therefore that the natural history of Peromyscus is among the best studied of any small mammal. For decades, the deer mouse has contributed to our understanding of population genetics, disease ecology, longevity, endocrinology and behavior. Over a century's worth of detailed descriptive studies of Peromyscus in the wild, coupled with emerging genetic and genomic techniques, have now positioned these mice as model organisms for the study of natural variation and adaptation. Recent work, combining field observations and laboratory experiments, has lead to exciting advances in a number of fields—from evolution and genetics, to physiology and neurobiology.

In 1993 Sin Nombre virus was recognized as the cause of hantavirus pulmonary syndrome (HPS) and the deer mouse (Peromyscus maniculatus) was identified as the reservoir host. Surveillance by the Centers for Disease Control and Prevention... more

In 1993 Sin Nombre virus was recognized as the cause of hantavirus pulmonary syndrome (HPS) and the deer mouse (Peromyscus maniculatus) was identified as the reservoir host. Surveillance by the Centers for Disease Control and Prevention and state health departments includes investigation to determine the likely site(s) and activities that led to infection, an environmental assessment of the home and workplace, and possibly rodent trappings at these sites. As of December 31, 1998, there were 200 confirmed cases from 30 states (43% case-fatality ratio). The national HPS case registry was examined to determine the incubation period of HPS. Review of 11 case-patients with well-defined and isolated exposure to rodents suggests that the incubation period of HPS is 9 to 33 days, with a median of 14-17 days. Case investigations allow a better understanding of the incubation time of HPS and may define high-risk behaviors that can be targeted for intervention.

The S and M segments of a hantavirus, enzymatically amplified from tissues of Cloudland deer mice (Peromyscus maniculatus nubiterrae) captured during 1985 in West Virginia, diverged from strains of Four Corners virus from the southwestern... more

The S and M segments of a hantavirus, enzymatically amplified from tissues of Cloudland deer mice (Peromyscus maniculatus nubiterrae) captured during 1985 in West Virginia, diverged from strains of Four Corners virus from the southwestern United States bymore than 16% and 6% at the nucleotide and amino acid levels, respectively. Phylogenetic analysis suggested that this virus strain (designated Monongahela) forms a possible evolutionary link between the Four Corners and New York hantaviruses.

Examination of standard metaphase chromosome preparations was employed to evaluate the use of resident small mammals as indicators of environmental mutagenesis. Small mammals of two species, (Peromyscus leucopus andSigmodon hispidus) were... more

Examination of standard metaphase chromosome preparations was employed to evaluate the use of resident small mammals as indicators of environmental mutagenesis. Small mammals of two species, (Peromyscus leucopus andSigmodon hispidus) were trapped over a two-year period at a locality polluted with a complex mixture of petrochemical waste products, heavy metals, and PCBs (polychlorinated biphenyls), and from two uncontaminated localities. Significant differences in levels of chromosomal aberrations between animals collected at the contaminated site and the uncontaminated sites were clearly indicated. Increases in lesions per cell and aberrant cells per individual were shown for both species at the contaminated site compared to the control sites. Levels of chromosomal aberrations were not different between the two control sites, however. This study suggests that cytogenetic analysis of resident small mammals is a feasible test model for assessment of environmental mutagenesis.

We used foraging trays to compare how oldfield mice, Peromyscus polionotus, altered foraging in response to the presence of fire ants, Solenopsis invicta, and in the presence of direct (predator urine) and indirect (sheltered or exposed... more

We used foraging trays to compare how oldfield mice, Peromyscus polionotus, altered foraging in response to the presence of fire ants, Solenopsis invicta, and in the presence of direct (predator urine) and indirect (sheltered or exposed microhabitat, moonlight, and precipitation) indicators of predation risk. Foraging reductions elicited by S. invicta were greater than reductions in response to well-documented indicators of risk (i.e., moonlit nights) and the presence of predator urine. The presence of S. invicta always led to reduced foraging, but the overall impact of S. invicta was dependent upon microhabitat and precipitation. When S. invicta was not present, foraging was greater in sheltered microhabitats compared to exposed microhabitats. S. invicta made sheltered microhabitats equivalent to more risky exposed microhabitats, and this effect was especially pronounced on nights without precipitation. The effect of S. invicta suggests that interactions with S. invicta may entail a potentially heavy cost or that presence of S. invicta may represent a more reliable indicator of imminent competition or predation compared to indirect cues of risk and predator urine. The presence of S. invicta led to reduced foraging under situations when foraging activity would otherwise be greatest (i.e., under vegetative cover), potentially reducing habitat quality for P. polionotus and the distribution of seeds consumed by rodents.

Babesia microti and Borrelia burgdorferi, the respective causative agents of human babesiosis and Lyme disease, are maintained in their enzootic cycles by the blacklegged tick (Ixodes scapularis) and use the white-footed mouse (Peromyscus... more

Babesia microti and Borrelia burgdorferi, the respective causative agents of human babesiosis and Lyme disease, are maintained in their enzootic cycles by the blacklegged tick (Ixodes scapularis) and use the white-footed mouse (Peromyscus leucopus) as primary reservoir host. The geographic range of both pathogens has expanded in the United States, but the spread of babesiosis has lagged behind that of Lyme disease. Several studies have estimated the basic reproduction number (R0) for B. microti to be below the threshold for persistence (<1), a finding that is inconsistent with the persistence and geographic expansion of this pathogen. We tested the hypothesis that host coinfection with B. burgdorferi increases the likelihood of B. microti transmission and establishment in new areas. We fed I. scapularis larva on P. leucopus mice that had been infected in the laboratory with B. microti and/or B. burgdorferi. We observed that coinfection in mice increases the frequency of B. microt...

Mice (Peromyscus leucopus noveboracensis) from a captivebreeding program were used to test the effects of three genetic breeding protocols (minimizing mean kinship [MK], random breeding, and selection for docility [DOC]) and inbreeding... more

Mice (Peromyscus leucopus noveboracensis) from a captivebreeding program were used to test the effects of three genetic breeding protocols (minimizing mean kinship [MK], random breeding, and selection for docility [DOC]) and inbreeding levels on sperm traits and fertility. Earlier, in generation 8, one DOC replicate went extinct because of poor reproductive success. By generation 10, spermatozoa from DOC mice had more acrosome and midpiece abnormalities, which were shown to be strong determinants of fertility, as well as lower sperm production and resistance to osmotic stress. In addition, determinants of fertility, including male and female components, were assessed in a comprehensive manner. Results showed that the probability (P) of siring litters is determined by sperm number, sperm viability, and midpiece and acrosome abnormalities; that the P of siring one versus two litters is determined by tail abnormalities; and that the total number of offspring is influenced by female size and proportion of normal sperm, showing the relative importance of different sperm traits on fertility. On average, males with 20% normal sperm sired one pup per litter, and males with 70% normal sperm sired eight pups per litter. Interestingly, the proportion of normal sperm was affected by docility but not by relatively low inbreeding. However, inbreeding depression in sperm motility was detected. In the MK group, inbreeding depression not only affected sperm motility but also fertility: An increase in the coefficient of inbreeding (f ) of 0.03 reduced sperm motility by 30% and translated into an offspring reduction of three pups in second litters. A genetic load of 48 fecundity equivalents was calculated.

To examine how developmental experiences alter neural pathways associated with adult social behavior, we crossfostered pups between the more aggressive and monogamous California mouse (Peromyscus californicus) and the less aggressive and... more

To examine how developmental experiences alter neural pathways associated with adult social behavior, we crossfostered pups between the more aggressive and monogamous California mouse (Peromyscus californicus) and the less aggressive and polygamous white-footed mouse (P. leucopus). Cross-fostered males became more like their foster parents when tested as adults. Male white-footed mice became more aggressive only in an aggression test in a neutral arena, whereas the territorial California mice became less aggressive in resident-intruder aggression test, as measured by attack latency. Only the species that displayed a change in resident-intruder aggression showed a change in arginine vasopressin (AVP) levels: cross-fostered California mice had significantly lower levels of AVP-immunoreactive (AVP-ir) staining than controls in the bed nucleus of the stria terminalis (BNST) and the supraoptic nucleus (SON) and a nonsignificant trend toward lower levels in the medial amygdala (MA). Neither species showed changes in AVP-ir staining in a control area, the paraventricular nucleus (PVN). The changes in AVP-ir staining in the BNST and SON may not be caused by stress because cross-fostering was not associated with changes in adult plasma concentrations of two steroid hormones, corticosterone and testosterone, that have been associated with stress-related alterations in AVP pathways. These results suggest that manipulating the early parental environment can directly alter both a neurotransmitter system and species-typical patterns of social behavior, but that these effects may vary between species and under different social contexts.

We examined seasonal dispersal patterns and timing of new infections of Sin Nombre virus (SNV), as determined by recent acquisition of antibodies (seroconversion), in deer mice (Peromyscus maniculatus) at two Montana rangeland study sites... more

We examined seasonal dispersal patterns and timing of new infections of Sin Nombre virus (SNV), as determined by recent acquisition of antibodies (seroconversion), in deer mice (Peromyscus maniculatus) at two Montana rangeland study sites over three years, 2004-2007. One study site was located in grassland habitat, and the other was located in shrub-steppe. In Montana, both of these habitats are commonly associated with peridomestic environments (in and around buildings). Peridomestic environments are where most reported human cases of hantavirus pulmonary syndrome (HPS) likely originate. Furthermore, deer mice dispersing from sylvan habitats colonize peridomestic environments. Thus, a thorough understanding of deer mouse dispersal is needed to help predict when humans are most at risk for exposure to SNV. We trapped mice at each study site twice a month, accumulating 85,200 trap nights of effort and capturing 6,185 individual deer mice a total of 22,654 times. We documented 980 dispersing individuals over 3 yr. We found positive correlations between the number of dispersing mice and number captured at each site, but there were no statistically significant seasonal differences in the number of dispersing mice. However, we did find a spring/ summer bias in mice that seroconverted and dispersed, suggesting that recently infected deer mice are most likely to enter settings where humans may be exposed to SNV during spring and summer.

Intensive small mammal trapping was conducted in 12 counties in New York state during 1998 Ð2000 to investigate the prevalence and site speciÞcity of the Lyme disease spirochete, Borrelia burgdorferi in, and presence of the blacklegged... more

Intensive small mammal trapping was conducted in 12 counties in New York state during 1998 Ð2000 to investigate the prevalence and site speciÞcity of the Lyme disease spirochete, Borrelia burgdorferi in, and presence of the blacklegged tick, Ixodes scapularis Say on, the wild mice Peromyscus leucopus RaÞnesque and Peromyscus maniculatus Wagner and other small mammal species. Previously captured mice (1992Ð1997) from throughout New York state also were recruited into the study, providing a total of 3,664 Peromyscus from 107 sites in 31 counties. Infection with B. burgdorferi was determined by polymerase chain reaction testing of ear tissue, and rates were determined by species, counties, and regions of the state. B. burgdorferi was detected in 10 small mammal species captured during 1998 Ð2000. Peromyscus captured from Dutchess County in the lower Hudson Valley had the highest infection rate of 21%. The next highest infection rates were in counties within the Capital District: Albany (18%), Rensselaer (17%), and Columbia (13%). From 4,792 small animals examined, we recovered 2,073 ticks representing six species from 414 individuals of 12 mammal species, including 1,839 I. scapularis collected from 315 Peromyscus trapped in Þve counties. I. scapularis were most often collected from animals trapped in Albany, Rensselear, and Dutchess counties. We used protein electrophoresis of salivary amylase to distinguish between P. leucopus and P. maniculatus species. I. scapularis burdens were 5.7 ticks per P. leucopus and 14.3 ticks per P. maniculatus.

Sin Nombre virus (SNV) establishes a persistent infection in the deer mouse, Peromyscus maniculatus. A strong antibody response occurs in response to SNV infection, but the role of the innate immune response is unclear. To address this... more

Sin Nombre virus (SNV) establishes a persistent infection in the deer mouse, Peromyscus maniculatus. A strong antibody response occurs in response to SNV infection, but the role of the innate immune response is unclear. To address this issue, we have initiated an effort to identify and characterize deer mouse cytokine and chemokine genes. Such cytokines and chemokines are involved in various aspects of immunity, including the transition from innate to adaptive responses, type I and type II responses, recruitment of leukocytes to sites of infection, and production of mature cells from bone marrow progenitors. We established a colony of SNV antibody-negative deer mice and cloned 11 cytokine and chemokine partial cDNA sequences using directed PCR. Most of the deer mouse sequences were highly conserved with orthologous sequences from other rodent species and functional domains were identified in each putative polypeptide. The availability of these sequences will allow the examination of...

Male and female mammals undergo profound hormonal changes during pregnancy, some of which are sufficiently dramatic to influence offspring survival. In order to understand the proximate mechanisms regulating the variability in... more

Male and female mammals undergo profound hormonal changes during pregnancy, some of which are sufficiently dramatic to influence offspring survival. In order to understand the proximate mechanisms regulating the variability in reproductive success within and between individuals, we monitored changes in fecal corticosteroid concentrations over the reproductive cycle in male and female oldfield mice (Peromyscus polionotus subgriseus) to test whether corticosteroid concentrations during pregnancy were associated with offspring survival. In females that successfully raised litters to weaning, fecal corticosteroid concentrations were low until mid-gestation and increased significantly towards term; in females that did not raise their pups to weaning, fecal corticosteroid concentrations were significantly higher at mid-gestation, and remained high until late gestation. The difference in fecal corticosteroid concentrations at mid-gestation between successful and unsuccessful females can be explained by the fact that successful females were lactating. Lactation has been associated with a down-regulation of the hypothalamic–pituitary–adrenal (HPA) axis and, accordingly, a decrease in plasma corticosterone (CORT) in several species, including humans. Males that successfully raised their litters had low fecal corticosteroid concentrations throughout their partner's pregnancy. Unsuccessful males, however, had significantly higher fecal corticosteroid concentrations at term than males that raised their pups to weaning. While these preliminary data require further investigation, we suggest that pre-partum fecal corticosteroid concentrations in males were responsible for the variability in reproductive success.

Fluorescence-labeled DNA probes constructed from three whole house mouse (Mus domesticus) chromosomes were hybridized to metaphase spreads from deer mouse (Peromyscus maniculatus) to identify homologies between the species. Mus Chr 7... more

Fluorescence-labeled DNA probes constructed from three whole house mouse (Mus domesticus) chromosomes were hybridized to metaphase spreads from deer mouse (Peromyscus maniculatus) to identify homologies between the species. Mus Chr 7 probe hybridized strongly to the ad-centromeric two-thirds of Peromyscus Chr 1q. Most of Mus 3 probe hybridized principally to two disjunct segments of Peromyscus Chr 3. Mus Chr 9 probe hybridized entirely to the whole Peromyscus Chr 7. Three Peromyscus linkage groups were assigned to chromosomes, based on linkage homology with Mus. The data also are useful in interpretation of chromosomal evolutionary history in myomorphic rodents.

The Lyme borreliosis agent Borrelia burgdorferi and the relapsing fever group species Borrelia miyamotoi co-occur in the United States. We used species-specific, quantitative polymerase chain reaction to study both species in the blood... more

The Lyme borreliosis agent Borrelia burgdorferi and the relapsing fever group species Borrelia miyamotoi co-occur in the United States. We used species-specific, quantitative polymerase chain reaction to study both species in the blood and skin of Peromyscus leucopus mice and host-seeking Ixodes scapularis nymphs at a Connecticut site. Bacteremias with B. burgdorferi or B. miyamotoi were most prevalent during periods of greatest activity for nymphs or larvae, respectively. Whereas B. burgdorferi was 30-fold more frequent than B. miyamotoi in skin biopsies and mice had higher densities of B. burgdorferi densities in the skin than in the blood, B. miyamotoi densities were higher in blood than skin. In a survey of host-seeking nymphs in 11 northern states, infection prevalences for B. burgdorferi and B. miyamotoi averaged ~0.20 and ~0.02, respectively. Co-infections of P. leucopus or I. scapularis with both B. burgdorferi and B. miyamotoi were neither more nor less common than random expectations. P. leucopus and I. scapularis . The null hypothesis was that B. burgdorferi and B. miyamotoi were maintained independently in environments where they co-existed. To evaluate this, we determined the frequencies of each type of infection in P. leucopus and ticks at the Connecticut field site and, additionally, in questing I. scapularis nymphs that had been collected in several other locations across the northeastern, mid-Atlantic, and north-central regions of the United States.

Blood meals by blacklegged ticks (Ixodes scapularis) on vertebrate hosts serve to transmit the agents of several zoonotic diseases, including Lyme disease, human babesiosis, and human granulocytic anaplasmosis, between host and tick. If... more

Blood meals by blacklegged ticks (Ixodes scapularis) on vertebrate hosts serve to transmit the agents of several zoonotic diseases, including Lyme disease, human babesiosis, and human granulocytic anaplasmosis, between host and tick. If ticks are aggregated on hosts, a small proportion of hosts may be responsible for most transmission events. Therefore, a key element in understanding and controlling the transmission of these pathogens is identifying the group(s) or individuals feeding a disproportionate number of ticks. Previous studies of tick burdens, however, have focused on differences in mean annual burdens between one or a few groups of hosts, ignoring both the strong seasonal dynamics of I. scapularis and their aggregation on hosts. We present a statistical modeling framework that predicts burdens on individual hosts throughout the year as a function of temporal-, site-, and individual-specific attributes, as well as the degree of aggregation in a negative binomial distribution. We then fit alternate versions of this model to an 11-year data set of I. scapularis burdens on white-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) to explore which factors are important to predicting tick burdens.

Adaptive modifications of heteromeric proteins may involve genetically based changes in single subunit polypeptides or parallel changes in multiple genes that encode distinct, interacting subunits. Here we investigate these possibilities... more

Adaptive modifications of heteromeric proteins may involve genetically based changes in single subunit polypeptides or parallel changes in multiple genes that encode distinct, interacting subunits. Here we investigate these possibilities by conducting a combined evolutionary and functional analysis of duplicated globin genes in natural populations of deer mice (Peromyscus maniculatus) that are adapted to different elevational zones. A multilocus analysis of nucleotide polymorphism and linkage disequilibrium revealed that high-altitude adaptation of deer mouse hemoglobin involves parallel functional differentiation at multiple unlinked gene duplicates: two ␣-globin paralogs on chromosome 8 and two ␤-globin paralogs on chromosome 1. Differences in O 2-binding affinity of the alternative ␤-chain hemoglobin isoforms were entirely attributable to allelic differences in sensitivity to 2,3-diphosphoglycerate (DPG), an allosteric cofactor that stabilizes the low-affinity, deoxygenated conformation of the hemoglobin tetramer. The two-locus ␤-globin haplotype that predominates at high altitude is associated with suppressed DPGsensitivity (and hence, increased hemoglobin-O 2 affinity), which enhances pulmonary O2 loading under hypoxia. The discovery that allelic differences in DPG-sensitivity contribute to adaptive variation in hemoglobin-O 2 affinity illustrates the value of integrating evolutionary analyses of sequence variation with mechanistic appraisals of protein function. Investigation into the functional significance of the deer mouse ␤-globin polymorphism was motivated by the results of population genetic analyses which revealed evidence for a history of divergent selection between elevational zones. The experimental measures of O 2-binding properties corroborated the tests of selection by demonstrating a functional difference between the products of alternative alleles.

Although there has been growing interest in the neuroanatomical and physiological mechanisms underlying aggressive behavior, little work has focused on possible mechanisms controlling natural plasticity in aggression. In the current... more

Although there has been growing interest in the neuroanatomical and physiological mechanisms underlying aggressive behavior, little work has focused on possible mechanisms controlling natural plasticity in aggression. In the current study, we used naturally occurring changes in aggression level displayed by female Peromyscus californicus across the estrous cycle and parallel changes in c-fos expression to examine possible brain regions involved in mediating this plasticity. We found that c-fos expression was increased in females exposed to a conspecific female intruder compared with control females in numerous brain regions thought to be involved in the control of aggression. More importantly, we found that c-fos increased in the bed nucleus of the stria terminalis (BNST) and ventral lateral septum (LSv) only in the more aggressive, diestrous females, and not in the less aggressive, proestrous and estrous females. Conversely, c-fos increased in the medial amygdala (MeA) across all stages of estrus compared with controls, suggesting the MeA is not involved in mediating changes in individual levels of aggression. Moreover, we found correlations between several measures of aggression and c-fos expression in the BNST and LSv but not the MeA, again suggesting a role in mediating aggression plasticity for the former two but not the latter brain region. We further hypothesize that the BNST and the LSv may be involved more generally in mediating natural changes in aggression, such as increases often observed after individuals win aggressive interactions against conspecifics.

Interactions among coinfecting parasites have the potential to alter host susceptibility to infection, the progression of disease and the efficacy of disease control measures. It is therefore essential to be able to accurately infer the... more

Interactions among coinfecting parasites have the potential to alter host susceptibility to infection, the progression of disease and the efficacy of disease control measures. It is therefore essential to be able to accurately infer the occurrence and direction of such interactions from parasitological data. Due to logistical constraints, perturbation experiments are rarely undertaken to directly detect interactions, therefore a variety of approaches are commonly used to infer them from patterns of parasite association in observational data. However, the reliability of these various approaches is not known. We assess the ability of a range of standard analytical approaches to detect known interactions between infections of nematodes and intestinal coccidia (Eimeria) in natural small-mammal populations, as revealed by experimental perturbations. We show that correlation-based approaches are highly unreliable, often predicting strong and highly significant associations between nematodes and Eimeria in the opposite direction to the underlying interaction. The most reliable methods involved longitudinal analyses, in which the nematode infection status of individuals at one month is related to the infection status by Eimeria the next month. Even then, however, we suggest these approaches are only viable for certain types of infections and datasets. Overall we suggest that, in the absence of experimental approaches, careful consideration be given to the choice of statistical approach when attempting to infer interspecific interactions from observational data.