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PubMed1980

Transmission studies with Sarcocystis idahoensis of deer mice (Peromyscus maniculatus) and gopher snakes (Pituophis melanoleucus).

Transmission studies with Sarcocystis idahoensis of deer mice (Peromyscus maniculatus) and gopher snakes (pituophis melanoleucus) were conducted to determine host specificity of various stages of the parasite. Sporocysts were not passed by four dogs or four cats fed infected skeletal muscle from deer mice. Seven white mice (Mus musculus) and 34 white-footed mice (Peromyscus leucopus) were negative for sarcocysts and liver meronts following oral inoculation with S. idahoensis sporocysts; however, excystation of sporocysts occurred in two white-footed mice killed four hours post inoculation (PI). A gopher snake orally inoculated with sporocysts remained negative for coccidia for two months PI. Three deer mice orally inoculated and three intraperitoneally (IP) inoculated with tachyzoites from liver meronts developed sarcocysts in their skeletal muscles similar to those seen in deer mice orally inoculated with sporocysts. Liver meronts were not found. Ten deer mice orally inoculated and 10 deer mice inoculated IP with bradyzoites from S. idahoensis sarcocysts remained negative for sarcocysts and liver meronts at necropsy 17 days PI.

Animals↗
PubMed1999

[2 new species of Stilestrongylus (Nematoda: Heligmonellidae) parasites of Peromyscus (Rodentia: Cricetidae) from Mexico].

Stilestrongylus peromysci n. sp. collected from Peromyscus difficilis (Hidalgo state, México), differs from other species in the genus in number of the spines (30) in the synlophe (both sexes) and because the eighth ray arises from the root of the ninth ray; S. hidalguensis n. sp. parasitised Peromyscus sp. and differs from all other congeneric species in the presence of 24 spines in the male synlophe and in the arrangement of the bursal rays (2-2-1 in the right lobe and 2-3 in the left lobe). A key to the species of Stilestrongylus is provided.

Animals↗
PubMed2005

Frequent Harderian gland adenocarcinomas in inbred white-footed mice (Peromyscus leucopus).

In 1997, three lines of inbred Peromyscus leucopus--GS109A, GS16A1, and GS16B--were acquired by the Peromyscus Genetic Stock Center. Since then, records have been kept on tumors detected by visible inspection of live animals. The inbred lines GS109A and GS16A1 presented tumors with frequencies substantially higher than that of the other inbred line or of random-bred P. leucopus stock. The average age of detection was 456 +/- 75 days (n = 24) for GS109A and 568 +/- 168 days (n = 12) for GS16A1 respectively. Surprisingly, the majority of the tumors (23 of 24 for GS109A and 8 of 12 for GS16A1) appeared to be Harderian gland lesions. During the same time period only a single tumor, a fibrosarcoma, was noted in the other inbred strain (GS16B), and one Harderian gland tumor was detected in the random bred stock. On the basis of the number of animals born to each group, tumor frequencies were approximately 22.7%, 8.3%, 0.67%, and 0.07%, for GS109A, GS16A1, GS16B, and randombred P. leucopus stock, respectively. The periocular tumors appeared to be highly malignant, with elevated mitotic indices, marked anaplasia, and metastases to regional lymph nodes and lungs. The tumors were readily transplantable to other animals of the same line. Among various other species, malignant Harderian gland tumors are relatively rare.

Adenocarcinoma↗
PubMed1987

The biparental care system of the California mouse, Peromyscus californicus.

Most knowledge of parent-offspring relations in mammals is derived from studies of mother-infant interactions. Male parental care has been less well studied. We explored maternal and paternal behavior of the California mouse, Peromyscus californicus. Six pairs of parents and their young were videotaped continuously for 12 hours/day, on alternate days from Days 1 to 31 postpartum. Males exhibit all parental activities and to the same extent as displayed by mothers, except lactation. Male parental behavior begins on the day of birth. Mothers and fathers spend substantial and equivalent amounts of time in the nest and in physical contact with pups throughout lactation. Males devote more time than females to licking pups, although females engage in more pup anogenital licking. Mothers nurse for at least 4 weeks, and fathers and mothers both build nests and carry young. The biparental care system of Peromyscus californicus affords an opportunity to develop a broader, more complete view of parent-offspring relations.

Animals↗
PubMed1995

Larval density and feeding success of Ixodes scapularis on two species of Peromyscus.

One potential mechanism for the regulation of tick populations is density-dependent feeding success on vertebrate hosts. In a series of laboratory experiments, we tested whether the density of larval Ixodes scapularis on the mice Peromyscus maniculatus and Peromyscus leucopus influenced tick feeding success. For both host species, the proportion of ticks feeding to repletion was constant (approximately 40-50%) over a range of infestation from 5 to 100 ticks per mouse. For P. leucopus, neither mass nor molting success of fed ticks was significantly related to tick density on the host. However, for P. maniculatus, we observed a statistically significant increase in molting success with increasing tick density on hosts, thus demonstrating facilitation rather than density-dependent regulation. Although results were not statistically significant, we observed a tendency for previously exposed P. leucopus to support lower tick feeding success than naive mice; however, even for previously exposed mice, tick feeding success was not density dependent. Our results do not support the notion that density-dependent feeding on hosts regulates density of I. scapularis populations at the numbers tested.

Animals↗
PubMed1996

Expressed Peromyscus maniculatus (Pema) MHC class I genes: evolutionary implications and the identification of a gene encoding a Qa1-like antigen.

To gain insight into the evolution of rodent major histocompatibility complex (MHC) class I genes and identify important (conserved) nonclassical class I (class I b) gene products and residues in these proteins, six Peromyscus maniculatus MHC (Pema) class I cDNA clones were isolated and sequenced. Five Pema class I cDNAs appeared most similar to mouse and rat classical class I (class I a) genes. One exhibited highest similarity to an H2 class I b gene, H2-T23 (encoding the Qa1 antigen). Phylogenetic trees constructed with Pema, RT1, and H2 class I sequences suggested that the lineages of some rodent class I b genes (e. g., T23 and T24) originated prior to Mus and Peromyscus speciation [>50 million years (My) ago]. Sequences of four Qa1-like proteins from three species permitted the identification of ten Qa1-specific amino acids. On the basis of molecular modeling, three residues showed the potential to interact with T-cell receptors and three residues (all corresponding to polymorphic positions among H2 class I a proteins) were predicted to influence antigen binding. The recognition of mouse Qa1 proteins by a subset of T-cells in influenced by a locus, Qdm, which encodes the H2-D leader peptide. One of the Pema class I cDNA clones classified as H2-K, D/L-like (class I a) is predicted to encode an identical peptide, implying that an antigen binding protein (Qa1) and the antigen to which it binds (the product of Qdm) has been conserved for over 50 My.

Amino Acid Sequence↗
PubMed1996

Phenotypic plasticity in skull and dental morphology in the prairie deer mouse (Peromyscus maniculatus bairdii).

Morphologists and systematists have long suspected that dietary consistency can affect skull and dental form in mammals. We examined plasticity of skull shape and tooth morphology in prairie deer mice (Peromyscus maniculatus bairdii) by feeding mice diets that differed in consistency but not nutritional quality. Shape differences were analyzed qualitatively and quantitatively, using both landmark-based morphometrics and traditional distance measurements. Mice fed a gruel made of laboratory chow soaked in water differed from those fed hard blocks of chow by a slight anterior shift in the incisor tips, a narrowed zygomatic plate, a reduction in size of the masseteric tubercles, an overall decrease in skull size in lateral view, and an increase in overall size in ventral view. Disparities between our results and previous studies may be due to the differences in behavior between the inbred, relatively inactive laboratory strains commonly used in experimental studies and the outbred, constantly active species used here. Also, in contrast to previous studies, the statistical analysis employed here took into account both family relationships of the animals and the large number of statistical comparisons performed. Failure to consider these factors would have resulted in an exaggerated estimate of the effects of diet on skull form and may taint other studies that have explored the same aspects of plasticity.

Animals↗
PubMed1983

Morphological and morphometric changes in the ovaries of white-footed mice (Peromyscus leucopus) following exposure to long or short photoperiod.

Two experiments were carried out with a total of 36 white-footed mice (Peromyscus leucopus) exposed to either long (LP) or short (SP) photoperiod for six weeks. Ovaries and uteri were weighed. Serial sections of the ovaries were processed for light microscopy. The total number of the interstitial gland cells, preantral and antral follicles with early and advanced stages of atresia as well as corpora lutea, was determined. Uteri from LP mice weighed significantly more than those from SP mice in both experiments. In contrast, the weight of ovaries from LP and SP animals only differed significantly in one experiment; this experiment also produced no obvious changes in the total number of corpora lutea. While interstitial gland cells of LP ovaries were hypertrophic and appeared mature, the interstitial gland cells of SP ovaries were of the degenerating cell type. The total number of follicles as well as their mean follicular diameters were higher in LP animals in comparison with SP animals. In addition, the percentage of antral follicles were increased and there were fewer signs of advanced stages of atresia in the LP group. It is suggested that the changes of the interstitial gland cell morphology combined with alterations of follicular growth during LP or SP appear to support intensified follicular growth.

Animals↗
PubMed1979

Reproductive failure and maternal-fetal relationship in a Peromyscus species cross.

Mating, fertilization, implantation, prenatal mortality, fetal and placental size, and placental ultrastructure were studied in intraspecific and interspecific crosses involving Peromyscus maniculatus and P. polionotus. Failure to mate was a major factor in interspecific crosses and was much more pronounced in crosses between P. polionotus females and P. maniculatus males than in the reciprocal cross. Failure of implantation following mating, however, was more pronounced in crosses between P. maniculatus females and P. polionotus males. Failure of implanted embryos to survive to term was a factor in crosses between P. polionotus females and P. maniculatus males. Comparison of the placental labyrinth of conceptuses from intraspecific and interspecific crosses revealed no differences at the ultrastructural level. The relationship of these observations to the evolution of isolating mechanisms in mammals and to physiological aspects of the developing maternal-fetal relationship are discussed. A model of placental and fetal size inheritance is presented.

Animals↗
PubMed1982

Effects of advancing age on the ultrastructure of pinealocytes in the male white-footed mouse (Peromyscus leucopus).

Quantitative comparison of pinealocyte ultrastructure in 3-month-old and 28-month-old male white-footed mice (Peromyscus leucopus) revealed decreases both in the area of the Golgi apparatus and in the number of dense-core vesicles. In contrast, no differences between these two age groups were noted in the areas of granular endoplasmic reticulum, vacuoles with flocculent content, lysosome-like bodies, or mitochondria. Nor were any changes between groups of mice apparent in pinealocyte nuclear or cytoplasmic areas, nuclear: cytoplasmic ratios, or the number of pinealocyte nuclei per unit area. Areas of unusual, annulate lamellae-like structures were increased in the pinealocytes of a group of 28-month-old mice. These observations suggest a possible age-associated decrease in the neurosecretory-like (but not ependymal-like) secretory process in the pinealocyte of white-footed mice.

Aging↗
PubMed1992

Tissue-specific metabolism during normothermy and daily torpor in deer mice (Peromyscus maniculatus).

Previous work with deer mice (Peromyscus maniculatus) has demonstrated that a significant acidosis occurs during daily torpor. In addition, carbohydrate levels are significantly lower, whereas fatty acid and ketone levels are significantly higher during torpor. The present study examined the effects of these in vivo acid-base and metabolite adjustments on in vitro 14C-glucose metabolism in tissues taken from normothermic and torpid deer mice. Glucose oxidation in liver and vastus lateralis taken from normothermic animals was reduced by a change in incubation temperature from 37 degrees C to 25 degrees C (liver, 0.44 to 0.23 mumoles/g.h; vastus, 0.66 to 0.25 mumoles/g.h), whereas heart from normothermic mice exhibited an increase from 0.57 to 0.99 mumoles/g.h at the lower temperature. Altering acid-base conditions or metabolite levels had no effect on glucose metabolism in the heart or liver. However, both of these factors significantly influenced metabolism in vastus. Vastus taken from normothermic mice had an increased glucose oxidation rate under the more acidic torpor conditions (0.25 to 0.33 mumoles/g.h), whereas a reduction in oxidation occurred when incubated with torpor substrate concentrations (0.33 to 0.22 mumoles/g.h). In vastus taken from torpid mice, changing acid-base state and metabolites to torpor levels resulted in a significant reduction in glucose oxidation (0.26 to 0.12 mumoles/g.h). Under most incubation conditions, glucose oxidation was significantly lower in tissues taken from torpid mice than in these tissues from normothermic mice, suggesting that adjustments in addition to changes in acid-base and substrate parameters may be necessary to account for metabolic modifications during daily torpor.

Acid-Base Equilibrium↗
PubMed1983

A possible mechanism of rapid luteolysis in white-footed mice, Peromyscus leucopus.

Adult female white-footed mice, Peromyscus leucopus, were exposed to long (LP) or short (SP) photoperiods for 6 weeks (experiment I). Another group of animals was kept for 6 weeks in SP, then injected SC with 30 micrograms prolactin twice daily for 2, 3, 4, or 6 days (experiment II). Ovaries from the mice in both experiments were weighed and serially sectioned for light microscopic examination of regressing corpora lutea. In experiment I, it was observed that vessels supporting corpora lutea were dilated, and that their endothelium was either undergoing necrosis or it was missing. Pronounced changes of luteal capillaries led to rupture and intraluteal hemorrhage, thus opening the capillary bed. Regressing luteal cells became segregated and seemed to invade the vascular system passively. They were seen as luteal cell thrombi in medullary veins. This luteolytic course termed "rapid luteolysis" was most apparent in SP ovaries. It differed from "retarded luteolysis," which represents the well-established luteolytic model of auto- and heterophagocytosis. In experiment II, there was a statistically significant decrease in ovarian weight 4 days after prolactin treatment in comparison with saline-treated controls. At the light microscopic level, signs of both rapid and retarded luteolysis were present, but not intensified. It is concluded: (1) The concept of rapid luteolysis represents a reasonable working hypothesis. (2) Prolactin, though luteolytic at the macroscopic level, failed to produce evidence of increased rapid or retarded luteolysis at the light microscopic level.

Animals↗
PubMed2001

Effect of capture and season on fecal glucocorticoid levels in deer mice (Peromyscus maniculatus) and red-backed voles (Clethrionomys gapperi).

The effect of confinement and season on fecal glucocorticoid (GC) levels in deer mice (Peromyscus maniculatus) and red-backed voles (Clethrionomys gapperi) was determined. Deer mice confined in a Sherman trap more than 4 h had fecal GC levels that were significantly higher than those in individuals that remained in a trap 4 h or less. However, this treatment may not be stressful for red-backed voles as neither plasma nor fecal GC levels were significantly elevated after 12 h of confinement. In addition, a clear temporal pattern in the secretion of fecal GCs was observed between mid June and early November in both species.

Animals↗
PubMed1995

Oxytocin changes in males over the reproductive cycle in the monogamous, biparental California mouse, Peromyscus californicus.

Levels of plasma oxytocin in male Peromyscus californicus were assessed across the reproductive cycle to provide a foundation for subsequent studies of the hormonal basis of paternal behavior and pair bonds. In Experiment 1, plasma oxytocin levels were significantly higher in expectant fathers than in virgin males or fathers. Plasma oxytocin increased in expectant fathers 1 day postcopulation and remained elevated for the first 15 days of gestation. Plasma oxytocin declined by Day 20 of gestation and oxytocin levels remained low in fathers throughout the lactational period. Oxytocin levels among expectant fathers did not differ between parental and nonparental males or between infanticidal and noninfanticidal males, suggesting that plasma oxytocin may not be involved in the prepartum onset of paternal behavior or the inhibition of infanticide. In Experiment 2, plasma oxytocin levels also did not differ between males that were parental or non-parental prepartum or postpartum. However, males separated from their mate and pups on the day of birth had elevated oxytocin levels on Day 3 postpartum compared to males that remained with their family, suggesting that disruption of the pair bond and/or absence of the young affects plasma oxytocin levels in males. This possibility remains to be determined.

Animals↗
PubMed2001

Testosterone, paternal behavior, and aggression in the monogamous California mouse (Peromyscus californicus).

Testosterone (T) mediates a trade-off, or negative correlation, between paternal behavior and aggression in several seasonally breeding avian species. However, the presence or absence of a T-mediated trade-off in mammals has received less attention. We examined the relationship between paternal behavior and territorial aggression in the biparental California mouse, Peromyscus californicus. In contrast to seasonally breeding birds, T maintains paternal behavior in this year-round territorial species. Castration reduced paternal behavior, whereas T replacement maintained high levels of paternal behavior. We hypothesize that T is aromatized in the brain to estradiol, which in turn stimulates paternal behavior. In contrast to paternal behavior, aggressive behavior was not reduced by castration. Interestingly, only sham males showed an increase in aggression across three aggression tests, while no change was detected in castrated or T-replacement males. Overall, trade-offs between aggression and paternal behavior do not appear to occur in this species. Measures of paternal behavior and aggression in a correlational experiment were actually positively correlated. Our data suggest that it may be worth reexamining the role that T plays in regulating mammalian paternal behavior.

Aggression↗
PubMed2000

Molecular phylogenetics of the Peromyscus boylii species group (Rodentia: muridae) based on mitochondrial cytochrome b sequences.

Variation in the mitochondrial cytochrome b gene (1143 bp) was examined to estimate the phylogenetic relationships of taxa within the Peromyscus boylii species group. In addition, phylogenetic relationships among the aztecus, boylii, and truei species groups were addressed. Maximum-likelihood, neighbor-joining, and maximum-parsimony (weighted and equally weighted) analyses produced similar topologies with P. boylii, P. beatae, P. simulus, P. stephani, P. madrensis, P. levipes, and three undescribed taxa from western Mexico forming a monophyletic unit. At least two of the undescribed taxa from western Mexico potentially represent species. Members of the P. aztecus species group formed a clade separate from the P. boylii group and should be recognized as a distinct species group. P. sagax, P. polius, and P. pectoralis, formerly placed in the P. boylii species group, generally formed an unresolved polytomy with the P. truei, P. aztecus, and P. boylii species groups. P. attwateri formed a sister taxon relationship with members of the P. truei species group (P. difficilis and P. nasutus) and should be considered a member of this group. Members of the P. truei species group did not form a monophyletic unit, indicating that this species group is not monophyletic and may be composed of two assemblages.

Animals↗
PubMed2000

Comparative phylogeography of Baileys' pocket mouse (Chaetodipus baileyi) and the Peromyscus eremicus species group: historical vicariance of the Baja California Peninsular Desert.

Phylogenetic analysis of 699 bp of the mitochondrial DNA (mtDNA) COIII and 450 bp of the cytochrome b genes among 14 species of coarse-haired pocket mice (Heteromyidae: Chaetodipus) corroborated previous indications that genetic divergence between species and species groups within the genus is generally very high, suggesting old times of divergence, and that the nominal species C. baileyi represents a highly divergent lineage within the genus, with no closely related extant sister species. Analysis of phylogeographic structure among 51 individuals from 12 localities throughout the geographic range of C. baileyi revealed three geographically separate mtDNA haplotype lineages. The oldest split separates populations east and west of the Colorado River, a pattern that is congruent with chromosomal and allozyme electrophoretic evidence. We consider the western populations to represent a distinct species, C. rudinoris. Within C. rudinoris, mtDNA haplotypes are further subdivided into northern and southern lineages along the Baja California Peninsula. Comparison of phylogeographic structure in the baileyi species group and the codistributed Peromyscus eremicus species group implies two points of codivergence and thus supports two historical vicariance hypotheses proposed for biotas distributed across the peninsular and continental warm deserts: a late Neogene (3 Ma) northern extension of the Sea of Cortéz and a mid-Pleistocene (1 Ma) midpeninsular seaway across Baja California.

Animals↗
PubMed1994

Genetic evidence for a hantavirus enzootic in deer mice (Peromyscus maniculatus) captured a decade before the recognition of hantavirus pulmonary syndrome.

To determine if the emergence of hantavirus pulmonary syndrome in the United States was a consequence of recent amino-acid altering mutations and/or genetic reassortment with pathogenic hantaviruses, we examined lung and spleen tissues from seropositive deer mice trapped in August 1983 in Mono County, California, for hantaviral RNA by reverse transcriptase-directed polymerase chain reaction. Alignment and comparison of 1485 nucleotides of the S and M genomic segments enzymatically amplified from these tissues indicated that these deer mice harbored a hantavirus which was genetically similar, differing by less than 2% at the deduced amino-acid level, to the hantavirus implicated in cases of hantavirus pulmonary syndrome occurring in the Four-Corners region of New Mexico, Arizona, Utah, and Colorado in 1993. The peromyscine rodent-borne hantaviruses were, in turn, genetically distinct from other well-characterized hantaviruses, diverging by approximately 30% from Prospect Hill and Puumala viruses at the nucleotide and amino acid levels. Phylogenetic analysis using the maximum parsimony, neighbor-joining, and unweighted pair-group methods indicated that the Peromyscus-derived hantavirus shared a common ancestry with arvicolid rodent-borne hantaviruses. Overall congruency of the phylogenetic trees based on the S and M genomic sequences supported the evolutionary position of the peromyscine rodent-borne hantaviruses. Our data also establish the existence of a hantavirus enzootic in deer mice long before the recognition of hantavirus pulmonary syndrome in the United States.

Amino Acid Sequence↗