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PubMedDate not supplied

Spontaneous occurrence of XYY primary spermatocytes in the Sitka deer mouse.

Analysis of microspread, silver-stained primary spermatocytes from chromosomally and phenotypically normal Peromyscus sitkensis revealed the occurrence of XYY zygotene and pachytene nuclei at low frequency in three of eight individuals examined. Observed pairing configurations of sex chromosomes included a trivalent and a Y bivalent-X univalent. The data suggest that premeiotic nondisjunction may be involved in the origination of XYY chromosomal conditions.

Animals↗
PubMedDate not supplied

Platinum coat color locus in the deer mouse.

Platinum coat color in the deer mouse, Peromyscus maniculatus, is an autosomal recessive trait marking a locus, pt, distinct from silver (si), albino (c), blonde (bl), brown (b), and agouti (a). Platinum deer mice are conspicuously pale, with light ears and tail stripe. The pewter trait is allelic with and phenotypically identical to platinum, and represents an independent recurrence of this mutant. The rate of recoveries of coat color mutations from wild deer mice is consistent with available data for recurring mutation rates balanced by strong selection against the recessive phenotype.

Alleles↗
PubMed1983

Photoperiodic stimulation of pubertal development in male deer mice: involvement of the circadian system.

Pubertal development in prairie deer mice (Peromyscus maniculatus bairdii) is accelerated by exposure of juveniles to a long-day photoperiod, and, conversely, retarded by exposure to short days. The purpose of the present study was to evaluate the possible involvement of the circadian system in the photoperiodic regulation of puberty. Weanling males, previously housed on a short-day light cycle of 6L:18D, were subjected to a "resonance" protocol in which they received one of the following light cycles: 6L:18D, 6L:30D, 6L:42D, 6L:54D, or 16L:8D. Post-weaning exposure to cycles of 16L:8D, 6L:30D, and 6L:54D stimulated reproductive organ growth as measured at 6 weeks of age. Exposure to cycles of 6L:18D and 6L:42D failed to stimulate reproductive development. These data support the hypothesis that young male deer mice use a circadian rhythm of responsiveness to light to measure photoperiodic time and, consequently, regulate pubertal development.

Animals↗
PubMed1988

A novel postcopulatory block of reproduction in white-footed mice.

Female white-footed mice (Peromyscus leucopus) fail to produce offspring when paired with a male from weaning until 150 days of age if an adult female or her odor is also present. The present study delineates more clearly which stage of the young female's reproductive cycle is inhibited by the chemosignal of the older female. Age at vaginal opening and first estrus are delayed by the presence of the older female, but only for about 10 days. The presence of a male counteracts this delay. Thus, the basis for the block is not a delay in puberty. The older female's presence does not influence the number of estrous cycles experienced during the 30 days following first estrus, nor does it influence the number of corpora lutea found at autopsy. The presence of sperm in the vaginae of young females indicates that they were copulating. Likewise, examination of embryos 2 and 3 days after copulation reveals normal developmental progress. However, implantation does not occur in young females that have been exposed to an adult female. Thus, the block occurs either during the final stages of embryo transport or in relation to the implantation process itself.

Animals↗
PubMed1993

Failure of cryptorchidism to suppress fertility in a tropical rodent.

The cane mouse (Zygodontomys brevicauda) breeds year-round on the hot llanos of Venezuela, only 8 degrees above the equator. The reproductive responses of the males of this species to heat were compared with those of a temperature zone rodent, the white-footed mouse (Peromyscus leucopus). When tested at different ambient temperatures, the movement of the testis in relation to the scrotum was similar in the two species, but the cane mouse's testis proved to be much more resistant to maintenance at core body temperature. In two experiments, cryptorchid cane mice experienced only a 24% and a 5% decrease in testis weight, and almost all of these males showed normal spermatogenesis and sperm storage. In comparison, cryptorchid white-footed mice showed a 58% drop in testis weight, a total inhibition of spermatogenesis, and a complete or near absence of stored sperm in all males. A mating test demonstrated that cane mice indeed remain fertile for at least 2 to 3 mo after being rendered cryptorchid. Normal numbers of these males when paired with females fathered normal litters. It is noted that the relative insensitivity of the testis of the cane mouse to heat might actually be more representative of scrotal mammals in general than is suggested by our present perspective, which has been developed on the basis of study of humans and mammals from cool climates rather than the tropics, where most mammals live.

Animals↗
PubMed1997

Photoperiod and steroid-dependent adjustments in hypothalamic gonadotropic hormone-releasing hormone, dopamine, and norepinephrine content in male deer mice.

The purpose of this study was twofold: 1) to examine photoperiod-dependent and steroid-dependent adjustments in hypothalamic GnRH and catecholamine content in male deer mice, Peromyscus maniculatus, and 2) to evaluate whether the commonly used measure of GnRH accumulation serves as an accurate indicator of altered reproductive function in short-day-housed rodents. Deer mice provide a unique animal model in which to evaluate the effect of short day length on the neural substrates directing reproductive function, since individual deer mice respond to short photoperiod with a range of neuroendocrine, endocrine, metabolic, and thermoregulatory adjustments. These adjustments, in part, result in two distinct reproductive phenotypes; reproductively competent "nonresponsive" mice, and gonad-regressed "responsive" mice. Reproductively mature males were maintained on either long (16L:8D) or short (8L: 16D) photoperiod for 8 wk. Thereafter, mice were phenotyped and either remained intact, castrated, or castrated and provided with an s.c. testosterone-filled silicone elastomer capsule releasing long-day or twice long-day levels of testosterone; mice were then housed for an additional 4 wk. At autopsy, plasma levels of LH and testosterone, hypothalamic GnRH content, and hypothalamic dopamine and norepinephrine concentrations were determined. Short photoperiod caused a similar increase in GnRH content in both short-day phenotypes, and this increase was primarily localized to the medial basal hypothalamus (MBH). Castration decreased GnRH content within the MBH of mice housed on both a long and short photoperiod. However, castration also reduced GnRH content within the medial preoptic area (MPOA) only among the short-day phenotypes. Steroid replacement at levels similar to those of intact long-day males restored GnRH content in all brain regions to levels of intact mice. On the other hand, steroid replacement at twice long-day levels restored GnRH content among long-day mice but reduced GnRH content among both short-day reproductive response groups, specifically within the MBH and MPOA. There were no dramatic effects of photoperiod or steroid treatment on catecholamine concentrations. But our results do suggest that the lateral preoptic area (LPOA) and MBH may be important sites of steroid feedback among mice exposed to short photoperiods and that the LPOA and diagonal band of Broca-septal regions may specifically be associated with catecholamine-directed photoperiod-induced adjustments of reproductive responsive mice. Taken together, these data show that GnRH accumulation is not the proximate signal directing seasonal changes in pituitary-gonadal function and cast doubt on the use of this factor as an accurate indicator of altered reproductive function.

Animals↗
PubMed1996

New pathogens for respiratory infections.

The emergence of new pathogens and the increasing antimicrobial resistance patterns of old pathogens are contributing factors to the high epidemiologic impact of lower respiratory tract infections. Hantaviruses, Chlamydia pneumoniae, and penicillin-resistant Streptococcus pneumoniae have recently gained most of the attention of international researchers. Hantavirus pulmonary syndrome has been confirmed in 100 cases with a very high mortality (52%). Risk factors for infection are peridomestic cleaning, agricultural activities, and an increased number of small rodents like deer mouse, mainly Peromyscus maniculatus. Pulmonary capillary leak and multiorgan involvement characterise Hantavirus pulmonary syndrome. Most recent reports rank C. pneumoniae among the three most common etiologic agents in community-acquired pneumonia, but it is also involved in chronic diseases such as chronic obstructive pulmonary disease and asthma. Several recent reports indicate the striking increase of penicillin-resistant S. pneumoniae strains. These data emphasize the crucial need for new therapeutic agents and more effective prevention programs.

Agriculture↗
PubMed2000

Adaptive significance of male parental care in a monogamous mammal.

Paternal behaviour presumably evolved because male care of young was critical for offspring survival. We report field evidence indicating that paternal behaviour enhances offspring survival in a monogamous mammal, the biparental California mouse, Peromyscus californicus. Male removal resulted in lower offspring survival in father-absent than in father-present families. New males took up residence with widowed females, but usually after females had stopped lactating, suggesting that the importance of the father is not primarily protection against infanticidal intruders but rather direct care of young.

Adaptation, Physiological↗
PubMed2002

Testosterone promotes paternal behaviour in a monogamous mammal via conversion to oestrogen.

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 first 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 confirm these results. Gonadectomized males treated with T + vehicle or E(2) + FAD showed higher levels of huddling and pup grooming behaviour than gonadectomized males treated with T + FAD or empty implants. Although E(2) is known to promote the onset of maternal behaviour to our knowledge our results are the first 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.

Animals↗
PubMed2002

Spatiotemporal patterns in the Hantavirus infection.

We present a model of the infection of Hantavirus in deer mouse, Peromyscus maniculatus, based on biological observations of the system in the North American Southwest. The results of the analysis shed light on relevant observations of the biological system, such as the sporadical disappearance of the infection, and the existence of foci or "refugia" that perform as reservoirs of the virus when environmental conditions are less than optimal.

Animals↗
PubMed2004

Molecular identification of two species of myiasis-causing Cuterebra by multiplex PCR and RFLP.

The myiasis-causing flies Cuterebra grisea (Coquillet) and Cuterebra fontinella (Clark) (Diptera: Oestridae) are normally parasites of mice, predominantly of the genus Peromyscus. The morphological similarities of these species and the existence of intermediate morphotypes bearing characters of both species make the identification of adults problematic; furthermore the identification of larvae is apparently not possible. This study presents two molecular approaches to discriminate between these species using specific band patterns: (i) species-specific primers designed in the cytochrome oxidase II (COII) region used in multiplex polymerase chain reaction (PCR) and (ii) restriction fragment length polymorphism (RFLP) on amplified segments of cytochrome oxidase I (COI) gene. Both methods were tested on Cuterebra larvae and on adult museum specimens. The two techniques showed a clear difference between C. grisea and C. fontinella, although species-specific primers were more successful than RFLP for degraded DNA. No intraspecific variation in RFLP and species-specific amplifications were detected for the two species of Cuterebra. The results exhibit discrepancies between molecular and morphological identification, suggesting that some of the adults were misidentified.

Animals↗
PubMed1990

Microgeographic distribution of immature Ixodes dammini ticks correlated with that of deer.

In order to determine whether the small-scale distribution of immature Ixodes dammini Spielman et al. corresponds closely to the activity patterns of white-tailed deer, Odocoileus virginianus (Zimmerman), these relationships were examined in a site on Long Island, New York, U.S.A. We first determined the extent and temporal pattern of adult ticks feeding on deer by examining twenty-three resident deer tranquilized during September-December 1985. I. dammini adults infested deer throughout this fall period, most abundantly during October and November. With radio-telemetry collars attached to deer we determined the relative frequency that they occupied 0.25 ha quadrats of the study site. During the following summer, we examined white-footed mice, Peromyscus leucopus (Rafinesque), that inhabited these quadrats and removed immature ticks from each. 8975 larval and 163 nymphal I. dammini were removed from 208 mice trapped in forty-three such quadrats. The frequency of deer using these quadrats was positively correlated with both the number of larval and of nymphal ticks per mouse. These results suggest that risk of I. damminiborne zoonotic disease may be decreased by locally reducing deer density in sites that experience intense human activity.

Animals↗
PubMed2006

Comparative phylogeography of eastern chipmunks and white-footed mice in relation to the individualistic nature of species.

Palaeoecological studies have demonstrated that ecological communities as a whole did not remain stable throughout the climatic fluctuations of the Quaternary. The result is that long-term associations of species cannot be inferred by contemporary associations in ecological communities. Therefore, the evolutionary significance of any contemporary ecological interactions among species and of the biotic community within which species have evolved also cannot be assumed from contemporary conditions. Comparative phylogeographic data provide a method to identify species within ecological communities that have shared biogeographic histories. We present an example of a long-term association between populations of two mammalian species, eastern chipmunks (Tamias striatus) and white-footed mice (Peromyscus leucopus), which are commonly associated with deciduous forest habitats. The distribution of mitochondrial DNA variation in T. striatus and P. leucopus from previously glaciated regions of the eastern United States support the hypothesis that, in at least part of their range, genetic lineages of the two species have expanded from similar population sources since the Last Glacial Maximum. In addition, the spatial concordance of genetic lineages of T. striatus and P. leucopus with the oak-savannah forest formations of Wisconsin and Illinois, suggest that populations associated with this community colonized the area in association with a set of arboreal species that comprise their deciduous forest habitat.

Animals↗
PubMed2006

Biological control agents elevate hantavirus by subsidizing deer mouse populations.

Biological control of exotic invasive plants using exotic insects is practiced under the assumption that biological control agents are safe if they do not directly attack non-target species. We tested this assumption by evaluating the potential for two host-specific biological control agents (Urophora spp.), widely established in North America for spotted knapweed (Centaurea maculosa) control, to indirectly elevate Sin Nombre hantavirus by providing food subsidies to populations of deer mice (Peromyscus maniculatus), the primary reservoir for the virus. We show that seropositive deer mice (mice testing positive for hantavirus) were over three times more abundant in the presence of the biocontrol food subsidy. Elevating densities of seropositive mice may increase risk of hantavirus infection in humans and significantly alter hantavirus ecology. Host specificity alone does not ensure safe biological control. To minimize indirect risks to non-target species, biological control agents must suppress pest populations enough to reduce their own numbers.

Animals↗
PubMed1982

Some corrections in Haemogregarine (Apicomplexa: Protozoa) nomenclature.

The nomenclature of three genera in the family Haemogregarinidae (Haemogregarina, Karyolysus, and Hepatozoon) has been reviewed and the following new names are introduced to replace homonyms or for previously unnamed species: haemogregarina carlosi n. nom., in the erythrocytes of the lizard Lacerta ocellata; Haemogregarina tincae n. nom., in the stomach and intestine of the tench Tinca tinca; Hepatozoon insectivorae n. sp., in the leucocytes of the shrews Sorex araneus and Crocidura leucodon; Hepatozoon krampitzi n. sp., in the leucocytes of the vole Microtus oeconomus; Hepatozoon peromysci n. sp., in the leucocytes of the deermice Peromyscus boylii and P. truei gilberti; and Hepatozoon pallida (Pessoa et al., 1971) n. comb., in the erythrocytes of the snake Thamnodynastes pallidus nattereri.

Animals↗
PubMed1988

Melatonin does not affect in vitro secretion of testosterone in white-footed mouse testis.

There is evidence that melatonin may exert its antigonadal effect by acting in the gonad to inhibit steroidogenesis. To explore this possibility a hormonally sensitive in vitro system of dispersed Peromyscus leucopus testis was used to assess the effects of melatonin on human chorionic gonadotropin (hCG)- and dibutyryl-cAMP (dbcAMP)-stimulated secretion of testosterone (T). At near-maximally stimulating doses of hCG and dbcAMP, melatonin in concentrations of 2 x 10(-12) M to 2 x 10(-7) M did not affect the rate of secretion of T in cells from active or regressed testes. These results do not support the idea that melatonin helps to regulate seasonal reproduction by acting in the testes to inhibit steroidogenesis.

Animals↗
PubMed1992

Studies on the biology of Ixodes dammini in the upper midwest of the United States.

The seasonal activity pattern of Ixodes dammini was monitored in south-central Wisconsin in 1989 and 1990. Immature tick activity and abundance were assessed by small mammal trapping (732 Peromyscus leucopus examined) and supplemented with flagging. Tick survival and molting times were evaluated by maintaining ticks in environmental chambers at field sites. Results indicate the biology of I. dammini in the upper midwest is similar to that previously reported from the eastern United States. One notable difference was that seasonal larval activity appeared broader (late April through October) and peaked earlier (on 9 July 1989 mean was 7.7 larvae/mouse; on 9 June 1990 mean was 7.3 larvae/mouse). Nymphal activity on P. leucopus peaked in May of both years (mean = 2.5 in 1989; mean = 1.8 in 1990). Bloodfed females placed in the field in early May 1990 oviposited in early June, and larvae emerged by early August. All bloodfed stages successfully overwintered at field sites.

Animals↗
PubMed2003

Transmission efficiency of the AP-variant 1 strain of Anaplasma phagocytophila.

Nymphal Ixodes scapularis ticks were collected from several sites in Rhode Island. DNA was extracted from a subset of these ticks, and PCR and DNA sequencing of the 16S rRNA gene were used to determine the ratio of Anaplasma phagocytophila-human agent (AP-ha) to a genetic variant not associated with human disease (AP-Variant 1). The remaining ticks were allowed to feed to repletion on either white-footed (Peromyscus leucopus) or DBA/2 (Mus musculus) mice. The engorged ticks, and blood samples drawn from each mouse at one-week intervals, were evaluated by PCR and DNA sequencing for the presence of AP-ha and Variant 1. Although a high percentage of the infecting ticks harbored AP-Variant 1, only AP-ha was amplified from the mouse blood samples. Because the A. phagocytophila variant did not establish an infection either in the natural reservoir of AP-ha, the white-footed mouse, or in a common research laboratory mouse (DBA/2), AP-Variant 1 may have an alternative natural reservoir, possibly the white-tailed deer.

Anaplasma phagocytophilum↗