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PubMedDate not supplied

Blonde, a new mutation in Peromyscus maniculatus affecting fur, skin, and eye pigmentation.

An autosomal recessive mutation affecting hair and eye pigmentation was discovered in the F2 progeny of wild-type deer mice, (Peromyscus maniculatus), trapped near East Lansing, Michigan. When homozygous, the mutation (designated as blonde, bl), reduces both black and yellow pigmentation deposited in the fur, reduces or eliminates pigmentation in the non-follicular melanocytes of the outer ear, peri-orbital skin and tail, slightly reduces the amount of pigmentation in the choroidal melanocytes, and completely eliminates pigmentation of the retinal epithelium.

Animals↗
PubMedDate not supplied

Coat color genetics of Peromyscus. I. Ashiness, an age-dependent coat color mutation in the deer mouse.

Ashy deer mice (Peromyscus maniculatus) were first discovered about 1960 in a wild population from Oregon. Although indistinguishable from the wild type at weaning, ashy deer mice become progressively grayer with subsequent molts. The trait is inherited as an autosomal recessive and the symbol ahy is assigned for the locus. The trait is distinctly manifest by 6 months of age, at which time homozygotes have white hairs on the muzzle and at the base of the tail. The amount of white gradually increases with age, but development varies greatly among animals. Some become virtually all white by 18 months. Implants of melanocyte-stimulating hormone induced production of pigment in depigmented portions of the coat, indicating that viable melanocytes were present. The ashy deer mouse model may be useful for further study of melanocyte function.

Aging↗
PubMedDate not supplied

Genetic variation for seasonal adaptation in Peromyscus leucopus: nonreciprocal breakdown in a population cross.

The genetic basis for adaptations to the diverse environments encountered by a wide-ranging species should be reflected in the phenotypes of hybrids between differentiated populations. We crossed mice from two ecologically different populations to determine whether adaptations to seasonality in Peromyscus leucopus, the white-footed mouse, display directional dominance or whether they are affected by specific interactions between genes. Connecticut mice (C) have many adaptations to seasonality that are reduced or absent in Georgia mice (G) and that affect both reproductive and thermoregulatory traits. Because these adaptations are cued by photoperiod, temperature, or both, parental and hybrid mice were acclimated to 13 degrees C in either long-day or short-day photoperiod, and several morphological, reproductive, and thermoregulatory traits were measured. Several traits, especially those involved in response to the environment, such as nest size at 13 degrees C, reproductive regression under short-day photoperiod, and molt to winter pelage, showed a non-Mendelian pattern of inheritance. However, there was a pronounced difference between maternal lineages in the F2 generation in that C-maternal F2 mice were less responsive to short-day photoperiod and cold than were the G-maternal F2 mice. Because these two classes of F2 mice are genetically equivalent, this breakdown cannot be explained as a disruption of epistatic gene interactions unless recombination rates are higher in the C-maternal lineage.

Adaptation, Physiological↗
PubMedDate not supplied

Morphological analysis of hair in the hr-2 mutant deer mouse (Peromyscus maniculatus).

Skin from 36 hairless deer mice (Peromyscus maniculatus) homozygous for the recessive hr-2 mutation were analyzed for structural defects in hair and hair loss. Comparison of mutant to wild-type hairs demonstrated characteristic abnormalities in cellular organization, hair shape, length, and fragility. Matings between mutants homozygous for the hr-2 gene and for a second mutation producing hairlessness in deer mice, hr-1, showed that these two genes were nonallelic. Structural abnormalities in hairs associated with the expression of this gene suggest that its primary effect may be on the epidermis.

Alopecia↗
PubMedDate not supplied

Coat color genetics of Peromyscus: II. Tan streak--a new recessive mutation in the deer mouse, P. maniculatus.

The first mutant tan streak deer mice appeared in the initial laboratory-bred generation of a stock of Peromyscus maniculatus nubiterrae collected in Macon County, North Carolina. Laboratory progeny from the original animals were bred and mated among themselves and to wild-type individuals. The tan streak phenotype is characterized by nearly complete absence of coat pigmentation, except for a pale tan patch or narrow stripe extending mid-dorsally posteriorly from the head. The band is frequently somewhat broader in the shoulder region, occasionally forming a cross-shaped pattern. There is no evidence of black eumelanin in any part of the coat. The eyes are fully pigmented, appearing black, and pigment is present in the skin of the ears and elsewhere. The trait is inherited as an autosomal recessive. The genetic locus is provisionally designated tns. Crosses between homozygous tan streak (tns/tns) animals and albino (c/c), ivory (i/i), non-agouti (a/a) and brown (b/b) deer mice produced only wild-type progeny, indicating that the tns mutation is not at any of these loci.

Alleles↗
PubMed1983

Mitochondrial DNA differentiation during the speciation process in Peromyscus.

We address the problem of the possible significance of biological speciation to the magnitude and pattern of divergence of asexually transmitted characters in bisexual species. The empirical data for this report consist of restriction endonuclease site variability in maternally transmitted mitochondrial DNA (mtDNA) isolated from 82 samples of Peromyscus polionotus and P. leucopus collected from major portions of the respective species' ranges. Data are analyzed together with previously published information on P. maniculatus, a sibling species to polionotus. Maps of restriction sites indicate that all of the variation observed can be reasonably attributed to base substitutions leading to loss or gain of particular recognition sites. Magnitude of mtDNA sequence divergence within polionotus (maximum approximately equal to 2%) is roughly comparable to that observed within any of five previously identified mtDNA assemblages in maniculatus. Sequence divergence within leucopus (maximum approximately equal to 4%) is somewhat greater than that within polionotus. Consideration of probable evolutionary links among mtDNA restriction site maps allowed estimation of matriarchal phylogenies within polionotus and leucopus. Clustering algorithms and qualitative Wagner procedures were used to generate phenograms and parsimony networks, respectively, for the between-species comparisons. Three simple graphical models are presented to illustrate some conceivable relationships of mtDNA differentiation to speciation. In theoretical case I, each of two reproductively defined species (A and B) is monophyletic in matriarchal genealogy; the common female ancestor of either species can either predate or postdate the speciation. In case II, neither species is monophyletic in matriarchal genotype. In case III, species B is monophyletic but forms a subclade within A which is thus paraphyletic with respect to B. The empirical results for mtDNA in maniculatus and polionotus appear to conform closely to case III. These theoretical and empirical considerations raise a number of questions about the general relationship of the speciation process to the evolution of uniparentally transmitted traits. Some of these considerations are presented, and it is suggested that the distribution patterns of mtDNA sequence variation within and among extant species should be of considerable relevance to the particular demographies of speciation.

Animals↗
PubMed1997

Phylogeography and molecular systematics of the Peromyscus aztecus species group (Rodentia: Muridae) inferred using parsimony and likelihood.

Mice of the Peromyscus aztecus species group occur at mid to high elevations in several mountain ranges in the highlands of Middle America (Mexico and Central America), a region of high endemicity. We examined the biogeography of this group by conducting phylogenetic analyses of 668 bp of the mitochondrial cytochrome b (cyt b) gene. Phylogenetic analyses under both parsimony and likelihood frameworks produced the same topologies, but estimates of nodal support were artificially high in weighted parsimony analyses. This difference is attributed to the inability of parsimony to optimize branch lengths when evaluating topologies. These data indicate that the P. aztecus-like populations from south and east of the Isthmus of Tehuantepec currently assigned to P. a. oaxacensis represent a distinct species, with genetic distances as high as 0.091. In addition, P. hylocetes is strongly divergent from Mexican populations of P. aztecus (genetic distances of 0.044-0.069), supporting the recognition of this taxon as a distinct species. The history of divergence in this group can be explained by a series of apparently early to middle Pleistocene vicariance events associated with glacial cycles. The Sierra Madre Occidental and Cordillera Transvolcanica each appear to be faunistically isolated, the Isthmus of Tehuantepec appears to have been a strong Pleistocene barrier, and the Sierra Madre Oriental has affinities with the Sierra Madre del Sur and the highlands of central Oaxaca.

Animals↗
PubMed1982

Geographic variation in Peromyscus leucopus: short-day induced reproductive regression and spontaneous recrudescence.

In order to determine if intraspecific differences exist in the photoperiodic control of the reproductive cycle of white-footed mice (peromyscus leucopus), 34 male and 60 female mice from either Connecticut (CT), Virginia (VA), or Georgia (GA) laboratory stocks were exposed to either a long (16L:8D) or short (9L:15D) photoperiod for up to 27 weeks. Reproductive status (testis length or the presence of a perforate vagina) of these mice was assessed every 1 to 2 weeks. After this time, the males were killed and testis length, testes weight, and seminal vesicle weight determined. Testis length in mice from CT and VA began to decrease after Week 5 of short-day exposure and reached a minimum at Week 13; this effect was less pronounced in the VA mice. Little change occurred in the GA short-day mice and in the three groups exposed to long photoperiods. Spontaneous gonadal recrudescence began after Week 17 in CT males and Week 15 in VA males, but was not yet complete at the end of Week 27. Similar results were obtained with the females. These results show that genetic differences exist in both the degree and duration of reproductive quiescence in this species.

Animals↗
PubMed1983

Effect of indomethacin on reproduction under laboratory and field conditions in deermice (Peromyscus maniculatus).

The purpose of this investigation was to determine the long-term effect of enterically administered indomethacin (a prostaglandin synthetase inhibitor) on reproduction in Peromyscus maniculatus (deermice) under both laboratory and field conditions. Indomethacin-coated wheat (1 mg/kg wheat) was provided to the experimental animals in the laboratory and under field conditions ad libitum. Rat chow was also provided to the animals in the laboratory. The laboratory data indicate that the number and size of the litters from the control breeding pairs were larger (number of litters=22; average number of pups/litter=4.9) than the experimental breeding pairs (number of litters=2; average number of pups/litter=2.5) over a 100-day experimental period. Field data indicate that the number of pregnant animals, the total number of animals, and mean juvenile males and females live-trapped decreased in the experimental group with respect to the control group during the experiment. The data suggest that deermice will consume indomethacin under both laboratory and field conditions, and that it effectively inhibits reproduction on a long-term basis. It is, therefore, possible that prostaglandin synthetase inhibitors may be used to control populations of rodent pests. Additionally, the data raise questions about the effect of long-term use of nonsteroidal analgesic compounds similar to indomethacin on human reproduction.

Animals↗
PubMed1983

Latitude of origin influences photoperiodic control of reproduction of deer mice (Peromyscus maniculatus).

Three subspecies of Peromyscus maniculatus originating from different latitudes were maintained from birth in light dark cycles that provided between 10 and 18 h of light per day. At 50 days of age, Chihuahua, Mexico mice (latitude of origin 27 degrees N) and South Dakota, U.S.A. mice (44 degrees N) kept in the 10L:14D photoperiod had reduced gonadal and seminal vesicle weights and a lower spermatogenic index than corresponding mice kept in a 14L:10D photoperiod. Some Chihuahua and South Dakota mice, apparently constituting nonphotoperiodic subpopulations, developed their gonads while kept in the short-day photoperiod. The critical day length for stimulation of sexual maturation was greater for mice from Manitoba, Canada (55 degrees N) than for mice from the lower latitudes. At 70 days of age, testes and seminal vesicle weights, and the spermatogenic index of Manitoba mice in the 14L:10D photoperiod, were lower than those of animals maintained in 16L:8D and 18L:6D photoperiods. Responsiveness to short day lengths was greater among adult South Dakota than adult Chihuahau mice and melatonin treatment significantly reduced testes weights of South Dakota but not of Chihuahua adult mice. Photoperiodic regulation of the reproductive system varies with latitude of origin. Differences in the critical day length necessary for stimulating development of functional reproductive activity and variations in the percent of photoperiodic animals within each subspecies, appear to contribute to latitudinal gradients in reproduction.

Animals↗
PubMed1985

Photoperiodic time measurement in the male deer mouse, Peromyscus maniculatus.

Weanling male deer mice, Peromyscus maniculatus, were exposed for three weeks either to light-dark (LD) cycles with periods (T=L+D) ranging from T=23 (1L:22D) to T=25.16 (1L:24.16D) or to 24-h LD cycles with photoperiods ranging from 1 (1L:23D) to 19 (19L:5D) h. Both the circadian locomotor activity rhythms and the response of the reproductive system to these LD cycles were assessed. The results demonstrate that the photoperiodic effectiveness of light depends on the phase of the light relative to the animal's circadian system, as marked by the circadian activity rhythm. Light falling during the animal's subjective night, from activity onset to at least 11.8 h after activity onset, stimulates growth and maturation of the reproductive system, whereas light falling during the rest of the circadian cycle is nonstimulatory.

Activity Cycles↗
PubMed1985

Pheromone-induced reproductive inhibition in young female Peromyscus leucopus.

Soiled bedding and urine from adult female white-footed mice (Peromyscus leucopus) were tested for their capacity to inhibit reproduction of young females. Test animals were given either physical or airborne contact with soiled bedding from adult females, adult female urine, clean bedding, or water from 21 to 150 days of age. Results indicate that reproductive inhibition is due to an airborne pheromone emitted by the adult females as a component of their urine. In the second experiment, young female mice were exposed to an adult female for 0, 1, 3, 6, 12, 18, or 24 h/day from 21 to 150 days of age. Results from this experiment show that exposure to adult females of as little as 3 h/day was sufficient to cause reproductive inhibition to occur. This phenomenon has important implications in terms of both female-female reproductive competition and socially mediated population regulation.

Animals↗
PubMed1986

Short photoperiod-induced gonadal regression: effects on the gonadotropin-releasing hormone (GnRH) neuronal system of the white-footed mouse, Peromyscus leucopus.

The peroxidase-antiperoxidase method was used to determine quantitatively the effect of short photoperiod-induced gonadal regression on the immunoreactive gonadotropin-releasing hormone (GnRH) neuronal system of female Peromyscus leucopus. In mice exposed to either long (16L:8D) or short (8L:16D) photoperiod, immunoreactive cell bodies were loosely organized into six groups: olfactory peduncle, diagonal band of Broca, septum, preoptic area (POA), anterior hypothalamus (AH), and basal hypothalamus. The POA and AH contain the largest number of cell bodies, which supply the major GnRH innervation to the median eminence (ME) and several extrahypothalamic brain sites. Exposure to short photoperiod increased the number of immunoreactive cell bodies within the anterior hypothalamus and preoptic area (AHPOA) and also increased the optical density for staining of immunoreactive cell bodies in the AHPOA and olfactory peduncle. The ME of mice exposed to short photoperiod had a higher density of GnRH fibers relative to that of mice exposed to long photoperiod, and the content of GnRH fibers in the rostral ME was correlated with the optical content for immunostaining of cell bodies in the AHPOA. These results are evidence that gonadal regression induced by short photoperiod (mediated by the pineal gland) involves alterations of GnRH neuronal activity. Notably, data from this study are consistent with the hypothesis that suppressed release of GnRH from neurovascular terminals in the ME, rather than lack of availability of the decapeptide, promotes gonadal regression.

Animals↗
PubMed1987

Duration of the melatonin pulse in the hypothalamus controls testicular function in pinealectomized mice (Peromyscus leucopus).

Forty-four pinealectomized white-footed mice (Peromyscus leucopus) were stereotaxically implanted with a guide tube-cannula assembly in the area of the preoptic/anterior hypothalamus. Easy insertion and removal of the melatonin-loaded cannula in the basal medial hypothalamus made it possible to examine whether duration of the melatonin pulse at the putative target site controls reproduction in mice. Mice receiving melatonin every day for 10 h during either the day or night underwent gonadal regression within 7 wk, as indexed by substantial decreases in combined testicular weight and seminal vesicle weight. Sperm production in these mice was also reduced or absent. Melatonin pulses given for 5 h, or as two 5-h pulses (separated by 3 h) did not alter reproduction in that these mice resembled sham-implanted controls. These results indicate that duration of the melatonin pulse, acting in the hypothalamus, may regulate seasonal reproduction in P. leucopus.

Animals↗
PubMed1988

Effects of photoperiod, beta-endorphin, and naloxone on in vitro secretion of testosterone in white-footed mouse (Peromyscus leucopus) testes.

The effects of the pro-opiomelanocortin-derived beta-endorphin (B-EP) and the opioid antagonist naloxone on in vitro secretion (accumulation of testosterone (T) in the medium) of T by testicular cells were assessed in adult white-footed mice (Peromyscus leucopus). Animals were housed under long days (16L:8D) to maintain testicular function or under short days (8L:16D) to induce gonadal regression. In vitro treatment with B-EP or naloxone did not affect basal secretion of T in dispersed cells from active or regressed testes. However, B-EP caused a dose-dependent reduction in secretion of T from cells stimulated maximally with human chorionic gonadotropin (hCG) or dibutyryl cyclic adenosine 3', 5'-monophosphate (dbcAMP). Conversely, naloxone enhanced maximal hCG- and dbcAMP-stimulated secretion of T in testicular incubates from both long- (1.5-fold) and short-day (3.5-fold)-exposed mice. The finding that the addition of naloxone to maximally stimulated cells increased further the secretion of T is evidence that B-EP may act to inhibit gonadotropin-stimulated secretion of T. Also, the stimulatory effect of naloxone on cells from regressed testes indicates that B-EP may be involved in suppressing production of T during the gonadally regressed state. Testicular B-EP-like immunostaining is present within the cytoplasm of interstitial cells and is not apparent in the seminiferous tubules. Together, these results support the idea that in P. leucopus endogenous opioid peptides in the testes may aid in the regulation of testicular function throughout the yearly breeding cycle.

Animals↗
PubMed1991

Characteristics of a genetic polymorphism for reproductive photoresponsiveness in the white-footed mouse (Peromyscus leucopus).

Wild populations of Peromyscus are often composed of individuals that vary greatly in their reproductive response to photoperiod. A population of white-footed mice (P. leucopus) from Michigan (43 degrees N) was subjected to mass selection in the laboratory both for and against reproductive photoresponsiveness for four generations. The first generation of selection yielded one line of mice in which about 80% of the individuals were classified as reproductively photoresponsive (i.e., with undeveloped reproductive tracts when reared in short days, 8L: 16D) and another in which only about 20% were reproductively photoresponsive. Some and perhaps most of this difference was accounted for by changes in degree of responsiveness to photoperiod rather than by alterations in the proportion of discrete responsive vs. unresponsive phenotypes. Alteration of critical day length was not a factor. Three more generations of selection failed to change the proportions noted above significantly. Although the genetic control of reproductive photoresponsiveness is undoubtedly complex, a single variable locus may be responsible for much of the heritable variation present in this population. These results also suggest that natural populations contain genetically determined phenotypes that are intermediate between absolutely photoresponsive and absolutely unresponsive. The factors that might promote maintenance of heterogeneity of reproductive photoresponsiveness in a wild population of rodents are considered.

Animals↗
PubMed1992

Photoperiod influences the critical caloric intake necessary to maintain reproduction among male deer mice (Peromyscus maniculatus).

The concept of critical day length is well established among rodents; reproductive function is maintained when day lengths are greater than some specific threshold. In addition to day length cues, seasonal breeding in deer mice can also be regulated by food availability. The caloric threshold necessary to support reproduction remains unspecified for seasonally breeding rodents. The present study examined the interaction between photoperiod and food availability on reproductive function in adult male deer mice (Peromyscus maniculatus). A critical caloric intake profile was constructed in long (16L:8D) and short (8L:16D) photoperiods; groups of deer mice in both photoperiods either received food ad libitum or 90, 80, or 70% of their individual ad libitum food intake for 10 wk. At autopsy, paired testes, epididymides, and seminal vesicles were removed and weighed. Body mass, total body fat, and total body water contents were also obtained. Short, as compared to long, day lengths inhibited the reproductive systems of male deer mice. However, food consumption interacted with photoperiod to affect reproductive function. Significant reductions in reproductive organ size as well as spermatogenic activity were observed among short-day mice after a 10% reduction in ad libitum food intake. Long-day animals required a 20% reduction in caloric intake to depress reproductive function. Body mass and total body water content were generally unaffected by either photoperiod or food consumption. Total body fat content was reduced in short- as compared to long-day mice. Individual reproductive responsiveness to short days increased as food availability decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Development and validation of a fecal testosterone biomarker in Mus musculus and Peromyscus maniculatus.

This is a report on the development and validation of an ELISA method to determine fecal testosterone levels, and on their evaluation as a biomarker for adverse effects of endocrine-disrupting chemicals on reproductive health using male rodents of the Peromyscus maniculatus and Mus musculus species as an animal model. The ELISA antibody had the highest specificity for testosterone (100%), followed by dihydrotestosterone (57.4%) and androstenediol (0.27%). Radiolabeled testosterone was injected i.p. into three mice. Fecal samples were collected, extracted, and analyzed by liquid scintillation counting. The ELISA was performed to characterize the excretion kinetics and metabolic fate of circulating testosterone. Solubilization of feces with 10% methanol overnight provided an extraction efficiency of 87% for all metabolites; an ethyl ether extraction was more selective for testosterone. The fecal excretion of the testosterone was a biphasic process with a majority of the radioactivity recovered in the first 24 hours. HPLC analysis revealed at least five testosterone metabolites in feces, with most metabolites being less polar than testosterone. This study forms the initial evaluation of what will become a field monitoring tool.

Androstenediol↗