Genetic (RAPD) diversity in Peromyscus maniculatus populations in a naturally fragmented landscape

We assessed the effects of long-term habitat fragmentation on genetic (random amplified polymorphic DNA) diversity in 11 Peromyscus maniculatus populations in the Lake Superior watershed. We analysed genetic structure at two spatial scales and the effect of island size and isolation on genetic diversity. At the regional scale, island populations differed from mainland populations (FST = 0.36), but mainland populations did not differ from each other (FST = 0.01). At the local scale, populations of the main island of Isle Royale differed from adjacent islet populations (P < 0.001; Monte Carlo approximation of Fisher's exact test), but not from each other (combined P = 0.63). Although geographical distance and genetic distance were positively correlated (P < 0.01; Mantel test), cluster analysis revealed some inconsistencies. Finally, genetic diversity was inversely related to isolation (P = 0.01), but had an unexpectedly negative relationship with island area (P = 0.03). The genetic structure of P. maniculatus populations in portions of the Lake Superior watershed appears to have been affected by long-term habitat fragmentation.     

Recovery of reproductive function by prairie deermice (Peromyscus maniculatus bairdii) from asymptotic populations

Prairie deermice greater than 100 days of age and non-reproductive in laboratory populations provided with surplus food and water were paired either with fertile mates or with other inhibited population animals. Following pairing, more than 75 per cent of all animals reproduced. The rates of reproductive recovery did not differ significantly between males and females. The average time required for reproduction by population animals paired with proven mates was less than that for pairs composed of population animals. The significantly slower rate of reproductive recovery for population pairs suggests that mutual stimulation is involved in recovery and is initially lacking or minimal in these pairs. A period of physiological and behavioural adjustment following removal from the populations appears necessary before reproduction. Mechanisms preventing reproduction within the populations are unknown.     

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.     

MHC class II beta sequence diversity in the deer mouse (Peromyscus maniculatus): implications for models of balancing selection

We studied population polymorphism at a major histocompatibility complex (MHC) class II beta gene in the deer mouse (Peromyscus maniculatus). We found that: (i) a single population of P. maniculatus has significantly higher levels of DNA and protein sequence diversity than worldwide samples from homologous genes in other taxa, including humans and mice; and (ii) the genealogy of allelic sequences in P. maniculatus deviates significantly from theoretical expectation under a model of symmetric balancing selection, in that alleles are relatively more divergent than expected. We suggest that the observation of high levels of pairwise allelic sequence divergence and deviation of the genealogy from theoretical expectation in P. maniculatus together provide support for a divergent allele advantage model for the maintenance of MHC polymorphism.     

Serum ACTH and adrenal histology in reproductively inhibited male prairie deermice (Peromyscus maniculatus bairdi)

Exogenous ACTH will cause adrenal hypertrophy and gonad dysfunction in reproductively capable male deermice. The ultrastructure of the zona fasciculata of inhibited animals is substantially different from ACTH stimulated animals which suggests that ACTH alone does not produce the inhibition. Although ACTH concentrations were variable, there was no clear demonstration that any differences existed between reproductively capable vs inhibited animals at the time when corticosterone is known to be elevated in the inhibited animals. A contributory role for ACTH in promoting inhibition is not ruled out, but neither is it likely that elevated ACTH alone accounts for the observed reproductive inhibition in animals taken from populations.     

Nuclear and mitochondrial DNA reveal contrasting evolutionary processes in populations of deer mice (Peromyscus maniculatus)

We investigated a major geographic break in mitochondrial DNA (mtDNA) haplotypes in deer mice, Peromyscus maniculatus, by analysing spatial variation in a 491‐bp fragment of the mtDNA control region from 455 samples distributed across a north–south transect of 2000 km in Western North America. To determine whether the mtDNA break was reflected in the nuclear genome, we then compared spatial variation in 13 nuclear microsatellites of 95 individuals surrounding the mtDNA break. Using a canonical correlation analysis we found that nuclear genomic variation was not correlated with mtDNA differentiation. The contrasting patterns of variation in mtDNA and nuclear DNA are consistent with a hypothesis of historic genetic drift that occurred in isolated refugia combined with recent gene flow between the formerly isolated refugial populations. A Mantel test of genetic vs. geographic distance revealed that recent gene flow between deer mouse populations has been high. We conclude that past vicariant events associated with Pleistocene climate changes together with recent gene flow have created the observed intra‐specific cytonuclear discordance in Western North America.     

Sixty polymorphic microsatellite markers for the oldfield mouse developed in Peromyscus polionotus and Peromyscus maniculatus

We isolated and characterized 60 novel microsatellite markers from the closely related oldfield mouse (Peromyscus polionotus) and deer mouse (Peromyscus maniculatus) for studies of conservation, ecological, quantitative and population genetics. We assessed all 60 markers in a wild population of Peromyscus polionotus rhoadsi (N = 20) from central Florida and found an average of nine alleles per marker and an observed heterozygosity (H_O) of 0.66 (range = 0.00–1.00). These polymorphic markers contribute to the growing number of genomic resources for Peromyscus, an emerging model system for ecological and evolutionary research.     

The influence of the social environment on sexual maturation of female deermice (Peromyscus maniculatus bairdi)

Population Ecology - Female deermice housed from weaning with groups of five females, five males or five males plus five females had significantly smaller uteri at 35–38 days of age compared...     

Population delimitation across contrasting evolutionary clines in deer mice (Peromyscus maniculatus)

Despite current interest in population genetics, a concrete definition of a "population" remains elusive. Multiple ecologically and evolutionarily based definitions of population are in current use, which focus, respectively, on demographic and genetic interactions. Accurate population delimitation is crucial for not only evolutionary and ecological population biology, but also for conservation of threatened populations. Along the Pacific Coast of North America, two contrasting patterns of geographic variation in deer mice (Peromyscus maniculatus) converge within the state of Oregon. Populations of these mice diverge morphologically across an east-west axis, and they diverge in mitochondrial DNA haplotypes across a north-south axis. In this study, we investigate these geographically contrasting patterns of differentiation in the context of ecological and evolutionary definitions (paradigms) of populations. We investigate these patterns using a new and geographically expansive sample that integrates data on morphology, mitochondrial DNA, and nuclear DNA. We found no evidence of nuclear genetic differentiation between the morphologically and mitochondrially distinct populations, thus indicating the occurrence of gene flow across Oregon. Under the evolutionary paradigm, Oregon populations can be considered a single population, whereas morphological and mitochondrial differentiations do not indicate distinct populations. In contrast, under the ecological paradigm morphological differentiation indicates distinct populations based on the low likelihood of demographic interactions between geographically distant individuals. The two sympatric but mitochondrially distinct haplogroups form a single population under the ecological paradigm. Hence, we find that the difference between evolutionary and ecological paradigms is the time-scale of interest, and we believe that the more chronologically inclusive evolutionary paradigm may be preferable except in cases where only a single generation is of interest.     

The relationship between food intake, body fat and reproductive inhibition in prairie deermice (Peromyscus maniculatus bardii)

1. Reproductively-inhibited deermice selected from four laboratory populations consumed significantly less food than reproductively-proven pairs. 2. Reproductively-inhibited animals predominantly, but not consistently, had reduced total body fat compared with reproductively capable deermice. 3. The per capita food consumption rate of two populations followed for 26 weeks since founding, decreased over time to about 65% of the daily intake of the proven animals used to found the populations. 4. An aggregation or "huddling" behaviour with concomitant reduction in thyroid hormone activity, possibly in response to the density of the "huddle", is suggested as an explanation for these observations.     

Comparative paternal and infanticidal behavior of sympatric white-footed mice (Peromyscus leucopus noveboracensis) and deermice (P. maniculatus nubiterrae)

We studied parental and infanticidal behavior in the field andlaboratory in two ecologically equivalent and sympatric congeners,white-footed mice, Peromyscus leucopus noveboracensis, and deermice,P. maniculatus nubiterrae. Despite their close phylogeneticrelationship and ecological similarity, various aspects of parentaland nesting behavior of the two species were significantly different.P. maniculatus males were more paternal than were P. leucopusmales in that they retrieved pups, nested with pregnant femalesand females with newborn pups, and formed longer associationswith females than did P. leucopus males. Thus, P. m. nubiterraeexhibited more pair-bonding (monogamous) characteristics thandid either P. leucopus or P. m. bairdi, as reported in otherstudies. The behavioral differences may represent the differentevolutionary history of the three subspecies. Infanticidal behavior,however, was similar in both species. Dispersing and unmatedmales killed strange pups placed in experimental test chambersin the field, whereas mated males did not kill pups within theirown home ranges. Resident females of both species were moreinfanticidal than were males, killing pups in 90% of the trials.The results support the sexual selection and resource competitionhypotheses for male and female infanticide, respectively. [BehavEcol 1991; 2: 38-45]     

Population density and seasonality effects on Sin Nombre virus transmission in North American deermice (Peromyscus maniculatus) in outdoor enclosures

Surveys of wildlife host-pathogen systems often document clear seasonal variation in transmission; conclusions concerning the relationship between host population density and transmission vary. In the field, effects of seasonality and population density on natural disease cycles are challenging to measure independently, but laboratory experiments may poorly reflect what happens in nature. Outdoor manipulative experiments are an alternative that controls for some variables in a relatively natural environment. Using outdoor enclosures, we tested effects of North American deermouse (Peromyscus maniculatus) population density and season on transmission dynamics of Sin Nombre hantavirus. In early summer, mid-summer, late summer, and fall 2007-2008, predetermined numbers of infected and uninfected adult wild deermice were released into enclosures and trapped weekly or bi-weekly. We documented 18 transmission events and observed significant seasonal effects on transmission, wounding frequency, and host breeding condition. Apparent differences in transmission incidence or wounding frequency between high- and low-density treatments were not statistically significant. However, high host density was associated with a lower proportion of males with scrotal testes. Seasonality may have a stronger influence on disease transmission dynamics than host population density, and density effects cannot be considered independent of seasonality.     

Oxygen consumption and carbon dioxide production in male prairie deermice (Peromyscus maniculatus bairdii) in different reproductive conditions and group densities

Natural and laboratory populations of Peromyscus exhibit a profound but reversible reproductive inhibition related to population density. Our earlier studies described the endocrine physiology of inhibited animals which resembles a condition of delayed puberty, but they did not reveal a primary mechanism for the induction and maintenance of the inhibition. These studies indicated that reproductive inhibition could be associated with an overall change in general metabolism. To test this hypothesis, oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in three groups of Peromyscus maniculatus males that were: 1) reproductively-proven, 2) reproductively-inhibited, or 3) recovered from inhibition. We found that the mean of the 2-hr period with the lowest VO2 (the Resting Metabolic Rate, or RMR) was significantly lower, and the mean Respiratory Exchange Ratio (RER) was significantly higher in reproductively-inhibited males compared with reproductively-proven males. In addition, previously inhibited males allowed to recover reproductive function had a significantly higher mean VO2, while the mean RER was not different from reproductively-proven males. Moreover, and contrary to some studies with other species, increasing the ambient carbon dioxide concentration or the caging densities to as high as six animals did not significantly affect oxygen consumption when compared with the corresponding values for individuals. Taken together, these findings indicate that the reproductive inhibition observed in P. maniculatus laboratory populations is causally associated with a significant reduction in general metabolism and that this metabolic reduction which is associated with reproductive-inhibition is not induced by a CO2 signal or induced by absolute density, per se.