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PubMed2001

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

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

Animals↗
PubMed2001

Thyroxine levels in agouti and non-agouti deer mice (Peromyscus maniculatus).

Total thyroxine was assessed by radioimmunoassay for 58 female deer mice of two subspecies (Peromyscus maniculatus bairdii and P. m. gracilis) and two color morphs (agouti and non-agouti). P. m. bairdii of both color-morphs had significantly higher mean thyroxine levels than P. m. gracilis. Non-agouti deer mice of both subspecies had significantly higher mean thyroxine levels than agouti deer mice. This is the first report of thyroid hormone differences associated with the non-agouti allele.

Aging↗
PubMed2002

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

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

Adrenal Cortex Hormones↗
PubMed2002

Developmental plasticity in aerobic performance in deer mice (Peromyscus maniculatus).

While several studies have examined the abiotic effects of altitude (low ambient temperatures and hypoxia) on the aerobic performance of small mammals, few have explored the effects of development and maturation at different altitudes on aerobic performance as adults. We examined the basal metabolism and aerobic performance of deer mice (Peromyscus maniculatus) under four different developmental and testing regimes: (1) reared (gestation through weaning) and tested at high altitude; (2) reared and tested at low altitude; (3) reared at low altitude and tested at high altitude after acclimation; and (4) reared at low altitude and tested in hypoxia without acclimation. We found that mice that developed and were tested at low altitudes had a higher aerobic capacity (both aerobic performance and basal metabolic rate) than those that developed, or were acclimated as adults, at high altitudes. In addition, we found that mice that developed at high altitude did not have a higher aerobic capacity than those that developed at low altitude and were acclimated to high altitude as adults. Both groups tested at high altitudes had higher hematocrits (% red blood cells) and hemoglobin than mice tested at low altitudes. Surprisingly, mice acclimated to low altitudes and given an instantaneous exposure to hypoxia did not suffer a depression in aerobic performance.

Acclimatization↗
PubMed2003

Relative roles of mutation and recombination in generating allelic polymorphism at an MHC class II locus in Peromyscus maniculatus.

The MHC class II loci encoding cell surface antigens exhibit extremely high allelic polymorphism. There is considerable uncertainty in the literature over the relative roles of recombination and de novo mutation in generating this diversity. We studied class II sequence diversity and allelic polymorphism in two populations of Peromyscus maniculatus, which are among the most widespread and abundant mammals of North America. We find that intragenic recombination (or gene conversion) has been the predominant mode for the generation of allelic polymorphism in this species, with the amount of population recombination per base pair exceeding mutation by at least an order of magnitude during the history of the sample. Despite this, patchwork motifs of sites with high linkage disequilibrium are observed. This does not appear to be consistent with the much larger amount of recombination versus mutation in the history of the sample, unless the recombination rate is highly non-uniform over the sequence or selection maintains certain sites in linkage disequilibrium. We conclude that selection is most likely to be responsible for preserving sequence motifs in the presence of abundant recombination.

Alleles↗
PubMed1992

Vegetation structure influences the burden of immature Ixodes dammini on its main host, Peromyscus leucopus.

To determine whether the relative abundance of immature Ixodes dammini (the vector of Lyme disease and human babesiosis) is related to habitat structure, we examined tick burdens on their main host, the white-footed mouse (Peromyscus leucopus), in 4 structurally diverse sites on Great Island, Massachusetts, USA. Vegetation structure at each site was quantified with respect to 25 habitat variables. Principal components analysis was used to reduce this set of habitat variables to seven new and orthogonal variables. Immature tick abundance varied widely among grids. Regression analysis of tick burdens on the habitat principal components showed that larval burdens were related strongly to the density of woody vegetation and negatively to herbaceous vegetation. Nymphal burdens were related negatively to herbaceous vegetation, but the relationship was not as strong as in the case of larvae. An experimental reduction in the abundance of white-tailed deer (Odocoileus virginianus), the main host of adult ticks, substantially reduced tick burdens and altered their relationships to habitat structure. Nymphal burdens were unrelated to habitat structure following deer removal. Manipulating habitat structure may have utility as a control strategy against this important vector.

Animals↗
PubMed2005

Peromyscus populations and their Cuterebra parasites display congruent phylogeographical structure.

The relationships between populations of the Deer Mouse (Peromyscus maniculatus) and the White-footed Mouse (P. leucopus) and their respective Cuterebra parasites were examined. Population genetic structure of hosts and parasites was inferred using cytochrome oxidase mitochondrial sequences of specimens from 7 populations. Genetic analyses revealed that isolation-by-distance applies for P. maniculatus and its associated parasite (C. grisea). A significant correlation was also observed between the genetic distances of these host and parasite species. Furthermore, populations of P. maniculatus and C. grisea from the North and South shores of the St Lawrence River were found to be significantly different. This structure may be explained by the St Lawrence River being a dispersal barrier for both species. A robust analysis of the other species pair (P. leucopus and C. fontinella) could not be performed because of limited sample sizes.

Animals↗
PubMed1993

A neuroanatomical correlate of paternal and maternal behavior in the biparental California mouse (Peromyscus californicus).

The medial preoptic area (MPOA) is important in the control of maternal behavior in rodents, and it is sexually dimorphic. This study demonstrates that the MPOA of nonparental virgin male Peromyscus californicus (n = 10) is larger than that of virgin females (n = 9) because of a significantly greater number of neurons in the MPOA of virgin males. However, this sex difference in MPOA volume disappeared when males and females became parents. Soma size increased significantly when females became mothers. These data suggest that maternal behavior may require a structural change in the MPOA, whereas paternal responsivity, which is normally inhibited in virgin males, may require a change in neuronal activity. Furthermore, these results underscore the importance of reproductive status in examination of sexually dimorphic nuclear structures.

Animals↗
PubMed2002

Medial preoptic lesions disrupt parental behavior in both male and female California mice (Peromyscus californicus).

California mice (Peromyscus californicus) are monogamous and naturally biparental, making them an ideal species in which to study the neural basis of paternal behavior. A male or female from each male-female pair was given an electrolytic or sham lesion in the medial preoptic area (MPOA), an area known to be critical for the expression of maternal behavior in rats, and retested for parental responsiveness. MPOA-lesioned males and females showed significantly longer latencies to show parental behavior and spent significantly less time near pups, sniffing pups, and licking pups than sham-lesioned mice. However, MPOA lesions did not reduce time spent hovering over pups. The results suggest that the neural mechanisms mediating paternal behavior are similar to those mediating maternal behavior in this species.

Animals↗
PubMed1983

Gonadal hormone activation of male courtship ultrasonic vocalizations and male copulatory behavior in castrated male deer mice (Peromyscus maniculatus bairdi).

The influence of testosterone (T), a 5 alpha-reduced metabolite of T, dihydrotestosterone, and an aromatized metabolite of T, estradiol, on 35-kHz ultrasonic calling and male copulatory behavior by male deer mice (Peromyscus maniculatus bairdi) was examined. Daily treatment with testosterone propionate (TP), dihydrotestosterone propionate (DHTP), or estradiol benzoate (EB) restored male ultrasonic calling in long-term castrated males. Both TP and DHTP restored male copulatory behavior, but EB was ineffective in facilitating copulation. Synergism of EB and DHTP action was observed; when subthreshold doses of EB (1 microgram/day) and DHTP (50 micrograms/day) were administered in combination, male ultrasonic calling and male copulatory behavior were activated. In relation to other comparative findings, these results indicate that the degree to which male sexual behavior is facilitated by 5 alpha-reduced androgens and/or estrogens is influenced by the species and the particular pattern of masculine behavior under consideration.

Animals↗
PubMed1988

Learning in mature mice (Peromyscus leucopus) subjected to deep hypothermia as neonates.

In certain species of nonhibernating rodents, although young nestlings cease breathing and heart action when their body temperature is lowered to near freezing, the nestlings need only be rewarmed to recover. This remarkable capacity for immediate recovery has been known many years, but long-range consequences of deep neonatal hypothermia have never before been investigated. Mice (Peromyscus leucopus) that had been exposed to four 2.5-hr episodes of deep (2-4 degrees C) hypothermia when 4-10 days old were later compared with littermate controls in their performance on two learning tasks. The two groups did not differ in their acquisition or extinction of a lithium-induced learned taste aversion to sucrose. Nor did they differ in learning to find a hidden platform in a swimming pool. Thus in a nonhibernating rodent species, deep hypothermia experienced neonatally--unlike similar hypothermia administered in adulthood--seems not to induce deficits in subsequent learning capabilities. The resistance of neonates to damage probably represents an adaptation, for their modest thermoregulatory abilities render them vulnerable to deep hypothermia in frigid environments.

Animals↗
PubMed1988

Kinship, familiarity, aggression, and dominance in deer mice (Peromyscus maniculatus) in seminatural enclosures.

This study was designed to test the effects of kinship and postweaning familiarity on male-male aggressive interactions in deer mice (Peromyscus maniculatus) in a more naturalistic situation than that of most tests of kin discrimination. Familiar males (i.e., those housed together from weaning) displayed significantly less aggression than unfamiliar males; kinship per se did not appear to affect levels of aggression. In addition, dominant males copulated more than subordinates and under some conditions sired more offspring. The postest copulatory patterns showed that the subordinate males ejaculated after fewer intromissions than did dominant males.

Aggression↗
PubMed1990

Tests of preferences of young deer mice (Peromyscus maniculatus bairdi) for siblings versus nonsiblings.

Three experiments were conducted to test the performance of young deer mice (Peromyscus maniculatus bairdi) in associating preferentially with siblings versus nonsiblings. In Experiment 1, neither males nor females preferred caged siblings versus nonsiblings. In Experiment 2, with full contact permitted, nonsibling males were in contact as much as were sibling males. In Experiment 3, with pairs of littermate pairs permitted full contact, there was no significant differential association. Although discrimination and preferences related to kinship have been demonstrated in some species, they cannot be assumed to be universal.

Aging↗
PubMed1990

Tests of preferences of adult deer mice (Peromyscus maniculatus bairdi) for siblings versus nonsiblings.

Seven experiments were conducted to test the performance of adult deer mice (Peromyscus maniculatus bairdi) in discriminating and preferring siblings versus nonsiblings. In two experiments there was no indication of preferences based on odor alone. Further, there was no indication of kin discrimination in a seminatural enclosure. There was some indication that in a test apparatus, estrous females associate preferentially with male siblings rather than nonsiblings. The effect appears dependent on the presence of siblings during development. Although the finding of a preference for siblings in estrous females is counter to expectations from an inbreeding avoidance approach, this is one of a variety of findings to suggest that not all animals avoid inbreeding all of the time.

Aging↗
PubMed1997

Effects of the nonagouti coat-color allele on behavior of deer mice (Peromyscus maniculatus): a comparison with Norway rats (Rattus norvegicus).

The agouti locus influences coat color by antagonizing melanocyte-stimulating hormone (MSH) at its receptor on pigment cells and may antagonize MSH in neural tissue. This study replicates work on rats to assess whether behavioral (neural) effects of the agouti locus are as similar across mammals as those on coat color. Handling, open-field, platform jump, and food-novelty tests were conducted on agouti and nonagouti deer mice (Peromyscus maniculatus) following protocols in C. A. Cottle and E. O. Price (1987). As with rats, nonagouti deer mice were less aggressive, less active, and easier to handle compared with their agouti counterparts. Nonagouti deer mice also groomed more than agouti subjects. Thus, behavioral effects of the agouti locus are conservative, and agouti may be an important modulator of melanocortins in neural as well as integumentary tissue.

Agouti Signaling Protein↗
PubMed2003

Vasopressin and the transmission of paternal behavior across generations in mated, cross-fostered Peromyscus mice.

The role of arginine vasopressin (AVP) in the nongenomic transfer of paternal behavior from fathers to offspring was examined in Peromyscus. Male California mice (P. californicus) exposed to fewer retrievals by white-footed mouse (P. leucopus) foster parents displayed fewer retrievals of biological offspring. In contrast, white-footed mice were retrieved equally rarely by California mouse foster parents and by biological parents and displayed no changes in pup retrieval behavior. AVP-immunoreactive staining in the bed nucleus of the stria terminalis may predict paternal behavior because it correlated positively with retrievals and with a score consisting of huddling, grooming, and time inside the nest. The authors discuss AVP as a possible mechanism by which early experience shapes adult paternal behavior.

Animals↗
PubMed1978

Poison-based taste aversion learning in deer mice (Peromyscus maniculatus bairdi).

A series of experiments tested the ability of mice of the native genus Peromyscus to form learned taste aversions. It was found that (a) the mice acquired a strong aversion after a single flavor/toxicosis pairing, (b) naive mice drinking a LiCl solution apparently began to experience toxic effects within 90 sec after the beginning of consumption, (c) the mice acquired a total aversion after a single flavor/delayed illness pairing when high doses of toxin were employed, and (d) the aversion produced by a single flavor/delayed-illness pairing was specific to the flavor paired with illness and was dependent on the contingency between the flavor and illness. Although these responses are qualitatively similar to those reported for domestic rats, the mice formed considerably weaker aversions than those previously reported for laboratory rats tested with the same weight-specific doses of LiCl.

Animals↗
PubMed1982

Testosterone acts as a prohormone to stimulate male copulatory behavior in male deer mice (peromyscus maniculatus bairdi).

In order to determine the importance of reduced and aromatized metabolites of testosterone for male sexual behavior in Peromyscus maniculatus bairdi, castrated males were treated with 5 alpha-reductase and aromatase inhibitors. In the first experiment, testosterone propionate (TP) activation of male copulatory behavior was blocked by the administration of the 5 alpha-reductase inhibitor 4-androsten-3-one-17-beta carboxylic acid (17 beta C). These treatments also prevented TP stimulation of seminal vesicles and ventral prostate gland weight. The inhibitory effects of 17 beta C were specific to testosterone, since 17 beta C did not prevent dihydrotestosterone propionate (DHTP) induction of male sexual behavior or seminal vesicles and ventral prostate gland weight increases. In the second experiment, TP activation of male copulatory behavior was prevented by the administration of the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD). The ATD did not interfere with DHTP activation of male reproductive behavior. Also, TP and DHTP stimulation of accessory sex organ weight was not blocked by ATD. On the basis of these data, it is suggested that metabolism of testosterone to both 5 alpha-reduced androgens and estrogens is obligatory for testosterone to reliably stimulate male sexual behavior in castrated male deer mice.

Androstatrienes↗