The concept of sexual segregation was 1st formally proposed by Charles Darwin. Among mammals, ruminants have been the focus of most research on this phenomenon. Sexual segregation has been defined traditionally as the differential use of space (and often habitat and forage) by sexes outside the mating season, but other hypotheses related to activity patterns of sexes recently have been forwarded. These new hypotheses, however, cannot explain the spatial separation of sexes or their differential use of habitats and forages. Sexual segregation should be considered in a niche framework wherein overlap on 1 niche axis is accompanied by avoidance on another, including space, diet, and habitat. Moreover, sexual segregation is scale sensitive, which limits the usefulness of a comparative approach in investigating differences among species or populations. Failure to discriminate between the potential evolutionary causes of sexual dimorphism in ruminants has led to confusion over whether polygyny or intersexual competition has led to sexual segregation. Neither exploitive nor interference competition, wherein males are competitively excluded by females, is a likely cause of sexual segregation. I suggest that the gastrocentric model, which invokes allometric and life-history differences between sexes, or risk of predation are the only hypotheses necessary to explain sexual segregation. Additional research, however, is necessary to verify some aspects of those hypotheses. The management and conservation of ruminants requires consideration that sexes behave as if they were different species, which holds consequences for estimating populations, manipulating harvest and habitats, and the potential spread of diseases and parasites and might have genetic consequences for some populations. This review attempts to resolve long-standing problems related to studies of sexual segregation, but much research remains to be accomplished, including more manipulative experiments.

Models of kangaroo populations have primarily focused on the prediction of population growth and distribution in relation to environmental variation at broad geographic scales. Current understanding of small-scale patterns in distribution, habitat breadth, and niche occupation is less complete. A powerful model of dispersion is ideal free distribution (IFD) theory. In plant–herbivore grazing systems, the most appropriate IFD models are those that allow for the incorporation of a standing crop of resources. Using eastern grey kangaroos (Macropus giganteus), we test the predictions of a previously described standing-crop IFD model where the number of consumers on a patch is proportional to the resource input rate, the standing crop of resources on all patches at equilibrium are equal (in the absence of interference), and the resource mortality rate is directly equivalent to the resource input rate, and is independent of the resource density (in the absence of interference). We make these comparisons at both the habitat and patch scale. At the habitat scale, we observed significant departures from these predictions that are consistent with the commonly reported occurrence of undermatching, whereas at the patch scale, little concordance with the predictions was observed. These results suggest that eastern grey kangaroos select for resources at the habitat scale but not at the level of the patch.

In the western United States, American badgers (Taxidea taxus) excavate large volumes of soil and create fan-shaped mounds while foraging for fossorial rodents. Densities of 790 mounds/ha were recorded on the Snake River Plain, west-central Idaho. More mounds were recorded from unburned compared with burned sites, but no differences were found between sites dominated by sagebrush (Artemisia tridentata wyomingensis) and winterfat (Krascheninnikovia lanata). Mounds and diggings occupied an average of 5–8% of the landscape and the mass of mounded soil averaged 33.8 kg, equivalent to 26 t/ha. The surface cover of plants, cryptogams, and litter increased, and bare ground decreased, as mounds aged. Excavation holes were present at 96% of active and crusted mounds compared with 31% of older recovering mounds. Sites with a greater density of shrubs tended to have a greater density of both badger mounds and ground squirrel diggings. Additionally, increased density of badger mounds was associated with increases in the density of ground squirrel holes and scratchings. These results indicate that badger mounds are a significant landscape structure and that badger activity is likely to have major impacts on soil and ecosystem processes in shrub–steppe ecosystems.

The association of microhabitat variables and capture (= occurrence) of striped skunks (Mephitis mephitis) was assessed at 3 sites in western Tennessee. Sixteen features were included in univariate and stepwise logistic regressions to investigate relationships between occurrence and habitat factors and to construct models predictive of occurrence. Accuracy of models was examined using jackknife procedures, and maps predictive of occurrence were developed through semivariance and kriging analyses. Average height of stand, hardwood snags >35 cm diameter at breast height, number of stems, distance to permanent water sources, and distance to open areas were among the habitat features most frequently found to be related to occurrence. Models derived from logistic regression predicted occurrence of the species at varying levels (56% to 75%). Overall, classification percentages appeared to be at a level useful for predicting the occurrence of M. mephitis, and mapping procedures sufficient for illustrating the association between occurrence and habitat.

Adult hispid cotton rats (Sigmodon hispidus) were collected from the field monthly for >2 years from populations near the northern edge of their range in Virginia and contemporaneously from south-central Georgia. Body measurements and weights were taken at capture, and after dissection embryos, corpora lutea, and placental scars were counted and measured; testes and seminal vesicles were dissected out, measured, and weighed. This allowed comparison of several life-history parameters between the populations and tests of several life-history hypotheses. The breeding season was up to 2 months longer in Georgia than in Virginia, where there was typically a 3-month or longer winter inactive period. Some reproductive activity was observed among Georgia females in all 12 calendar months, whereas pregnancies were never observed in Virginia during November–February. Average litter sizes were significantly higher in Virginia (5.91 ± 1.41, up to 13) than in Georgia (5.16 ± 1.79, up to 9); this difference may partly result from a higher incidence of embryo resorption and prenatal mortality in the Georgia population, primarily in the cooler 6 months of the year. Virginia rats averaged significantly smaller for both sexes, but this was likely the result of a younger age distribution. Among reproductive males and females, no body-size differences were found between populations except that pregnant females from Virginia averaged significantly longer. Fifty percent and 75% of the random sample of adult females and males, respectively, were reproductively active in Georgia, whereas only 35% and 40% were reproductively active in Virginia. Spermatogenically active males in Virginia had significantly greater relative gonadal mass than their Georgia counterparts. Overwinter survival of parous females was lower in Virginia. Virginia populations, in a more seasonal environment, displayed a more r-selected life history, with greater reproductive allocation, faster growth (except over winter), higher mortality, and less iteroparity.

Species demonstrating intraspecific variation in social systems can be powerful models for understanding evolution of those systems. As a group, marmots exhibit several types of spacing systems, usually involving some degree of territoriality. Researchers have described populations of 1 species, the woodchuck, Marmota monax, as territorial and as nonterritorial, and such variation has been linked to ecological conditions. I used direct observations of individually recognized animals to describe the spacing system of a high-density population of Marmota monax in southern Maine. This population exhibited intrasexual territoriality. Home range overlap generally was higher between males and females than between same-sex individuals, and woodchucks tended to approach more members of the same sex more quickly compared with members of the opposite sex. Time spent scent marking varied across the active season but did not vary by sex. Males had larger home ranges than females, and home range sizes varied over time, perhaps in response to resources. Amount of overlap also was greater in some years than others, and such changes may be related to kinship. Philopatry and timing of dispersal also vary in this species and have implications for the evolution of sociality.

We assessed the geographic distribution of the Mexican prairie dog (Cynomys mexicanus) by comparing historical reports, data from a 1996 study, and our distribution estimations from 1999. We located 54 active and 22 inactive prairie dog colonies, determined size for each one, and evaluated whether colony size and isolation had an impact on the persistence of colonies and likelihood for recovery. We estimated a current total distribution of 322 km² within the Mexican states of Nuevo León (234 km²), Coahuila (82 km²), and San Luis Potosí (6 km²). The occupied range of the Mexican prairie dog suffered a 33% reduction from 1996 to 1999 and an overall reduction of 74% when compared with its documented historical range. We found no relationship between isolation and colony size for active colonies, although geographic isolation can result in decreases in the chances of colonies surviving stochastic events. Other challenges for the recovery of this species include the increased rate of habitat loss and deterioration, and landscape desertification factors.

We provided supplemental food to hispid cotton rats (Sigmodon hispidus) in northeastern Kansas to test for restriction of movements in the presence of additional resources. We estimated movements as the mean squared distance from the centroid of locations for each individual and tested for changes in movements on 2 time scales using mark–recapture data. Movements within a 3-day interval varied with sex, season, and reproductive condition, but we found no significant changes in response to supplemental food. Movements over an individual's entire 1–6-month tenure on our area decreased with added food. Hence, adding food at regularly spaced, point sources did not seem to influence daily movements but reduced the tendency of individuals to shift centers of activity over longer time intervals.

We determined water budget in the reproducing female common spiny mouse (Acomys cahirinus) offered ad libitum millet seeds and water. We hypothesized that the proportional increase in water input in lactating mice compared with nonreproducing mice would be greater than the proportional increase in energy intake, given that more water would be required for higher heat production and for milk production. Females gave birth to 1 or 2 offspring; results of water budget and energy intake did not differ among litter sizes and were combined. Lactating females increased water input and energy intake by 59.1% and 35.2%, respectively, compared with nonreproducing females, confirming our hypothesis. Milk production (1.04 ml/day) accounted for 29% of the difference in water output between lactating and nonreproducing spiny mice.

Geoffroy's cat (Oncifelis geoffroyi) is a little-known South American felid. We report here the first detailed data on its food habits and variations among 3 areas of the Argentine Pampas grassland. Analysis of 421 scat samples showed a relatively narrow trophic niche, dominated by vertebrates, especially small rodents. Despite a wide overlap in diet composition, geographical variation was found in frequency of occurrence of primary food categories, presence of secondary food items, and mean weight of vertebrate prey. These differences seem to be related to variation in food availability and suggest that Geoffroy's cats are able to show a certain degree of adaptability in foraging behavior.

Neotropical bat species may coexist because they forage in different places or in different ways. The small insectivorous orange-bellied bat, Lampronycteris brachyotis (Phyllostomidae), differs from coexisting gleaners in key ecomorphological characteristics, including longer, narrower wings and smaller ears. Using telemetry, we measured range size, range use, and activity patterns, and assessed habitat preferences for 9 individuals for 50 nights over 4 months on Barro Colorado Island, Panama. The bats spent the night in individual, medium-sized (22–27 ha) foraging areas within forested regions close to shorelines, up to 4 km away from the day roost. Each bat spent most of its time in a small (3–5 ha) core area. Foraging flights ranged from a few s to more than 70 min. Total flight time per night averaged 3.5 h and flight distance was estimated to be 60 km. There were no distinct activity peaks. Our tracking data suggest that L. brachyotis primarily forages in the canopy, where it gleans insects from vegetation in a combination of perch hunting and continuous flight. This species may also catch insects in air above the canopy. This unique behavior among gleaning insectivorous phyllostomids corroborates our hypothesis that morphological adaptations combined with behavioral flexibility reflect distinct differences in foraging strategies and microhabitat selection. We conclude that differential use of space and hunting strategies promotes coexistence among the species-rich guild of Neotropical insectivorous gleaning bats.

Prairie voles are a monogamous species and males show paternal behavior. After mating, paternal responsiveness increases gradually during the gestation period, peaking before young are born. We examined the importance of cohabitation with a female and the time course for a gradual intensification of paternal care. Males housed with their brothers since weaning were separated. Each male was housed alone, with a strange female, or with a brother. A male housed with a female remained with her either until mating occurred or throughout gestation. Males in each group were tested for paternal behavior 3 times, in early, mid and late gestation periods. Males that were housed alone attacked the young more than those housed with another vole. A male exposed to a female, whether he had mated or not, engaged in more parenting than a male exposed to a brother. A male that remained with his mate during the gestation period was more parental than an isolated male that was housed alone. Contact with another vole reduces infanticidal tendencies; brief physical contact with a female, with or without mating, intensifies paternal responsiveness; and further cohabitation is not essential.

As evidenced by domesticated species, generations in captivity can alter morphology in mammals and other taxa. This study examined morphological change in a captive wild mammal, the oldfield mouse (Peromyscus polionotus subgriseus). Specifically, cranial and mandibular size and shape were compared using geometric morphometric techniques. These data show that magnitude of change increased with generations in captivity, but physical changes between populations were not cumulative or progressive. Observed changes were likely due to relaxed selective pressures associated with captivity, coupled with founder effects. The results of this study have significant implications for captive management of mammals, particularly for those populations used for conservation. Biologists who bring animals into captivity need to be aware that morphological changes, as well as other changes, most likely have or will occur over generations in captivity. This, combined with changes taking place in wild populations, is likely to result in captive populations that are significantly different from their wild counterparts.

Scent marking is a common form of territorial demarcation in mammals and differential marking by the sexes may select for differences in scent gland developmental rates or size. Rates of marking reflect level of defense and so behavioral dimorphism in marking by the sexes may select for dimorphism in scent structures. Eurasian beavers (Castor fiber) are monogamous, territorial mammals that show some behavioral dimorphism in territoriality. Beavers have 2 primary scent structures, anal glands and castor sacs. Anal gland secretion appears to serve as a family or individual identifier. Castor fluid is the main source of chemical signals used for marking territories. We examined beavers collected from 3 different habitats, namely streams, creeks and tarns (small lakes), which varied in the density of beaver sites. The objectives of this study were to examine if morphological attributes of Eurasian beaver scent structures reflected differences in adult beaver territorial function or in the ontogeny of the sexes. We hypothesized that male beavers would have larger castor sacs and anal glands, and that beavers from sites of greater density, and thus greater rates of intrusion, would have larger castor sacs and anal glands. Our results showed that investment did not differ by habitat type. Although the combined weight of the scent structures did not differ between the sexes, males developed significantly larger anal glands but somewhat smaller castor sacs than females. Total investment to scent structures may be limited but allocation is flexible. Males patrol the territory more extensively and may benefit by releasing anal gland secretion to signal their identity to potential intruders. Higher rates of marking may decrease castor sac size by reducing the amount of stored scent material. Hence, even in monogamous mammals, sexual dimorphism can arise from behavioral dimorphism.

Gender identification of sexually monomorphic mammals can be difficult. We used analysis of zinc-finger protein (Zfx and Zfy) DNA regions to determine gender of 96 beavers (Castor canadensis) from 3 areas and used these results to verify gender determined in the field. Gender was correctly determined for 86 (89.6%) beavers. Incorrect assignments were not attributed to errors in any one age or sex class. Although methods that can be used in the field (such as morphological methods) can provide reasonably accurate gender assignments in beavers, the genetic method might be preferred in certain situations.

Phylogenetic methods were used to analyze cytochrome-b sequences (n = 257; 560 base pairs) from Peromyscus keeni (Keen's mouse) collected from 23 islands of the Alexander Archipelago and 6 mainland locations in southeast Alaska and western Canada. Although P. keeni is ubiquitous across this region, island populations are genetically distinctive. Genetic structure of extant populations of P. keeni appears to have been more heavily influenced by vicariance than post-glacial colonization. Populations of P. keeni might have survived in coastal refugia during the last glacial maximum (15 × 10³ years ago). Island area was significantly correlated with 2 of 3 genetic diversity measures whereas island isolation was not. Areas with divergent populations were discovered, but were largely inconsistent with 3 of 5 currently recognized subspecies. Cryptic variation was detected in 8 areas not previously identified by morphologic analyses.

DNA sequences from the mitochondrial cytochrome-b gene were used to examine the composition and phylogenetic relationships of the Peromyscus truei species group. Thirty-one individuals from the southwestern United States and Mexico were examined. Results indicated that 6 Peromyscus species (attwateri, difficilis, gratus, nasutus, pectoralis, and truei) compose the P. truei species group and that the group should be divided into 2 species assemblages. The relationship of the P. truei species group to the P. boylii and P. aztecus species groups was unresolved, indicating a close association of these 3 groups. In addition, levels of sequence divergence between sister taxa were higher than those reported for other sister species of Peromyscus.

The genus Cratogeomys, particularly members of the Cratogeomys gymnurus species group, account for much of the high species diversity of pocket gophers in the Trans-Mexican Volcanic Belt. Recent molecular studies of this species group have shown strong discordance between genetically defined clades and current species taxonomy. Accordingly, we investigated relationships among the 5 species in the C. gymnurus species group using mitochondrial and nuclear DNA, chromosomes, and morphological characters. Although quantitative morphometrics provided little discrimination among species or clades within this group, the molecular data sets were consistent in identifying 5 allopatric clades, none of which corresponded to any of the 5 currently recognized species. Four of these 5 genetically defined clades lack clear diagnosability, and so are grouped into the single polytypic species, C. fumosus. The fifth clade is diagnosable based on multiple characters, including nuclear genotype, chromosomal diploid number, parasite fauna, and qualitative morphological characters. Accordingly, we resurrect Merriam's (1895) species planiceps to represent members of this clade, which occurs in the Volcán de Toluca and Valle de Bravo regions of central Mexico. Based on the observation that differences in diploid number usually signal reproductive isolation between populations of pocket gophers, we hypothesize that C. fumosus and C. planiceps are reproductively incompatible. We provide synonymies and descriptions for these 2 species, along with a key to this species group, which is now called the C. fumosus species group.

Historically, specimens representing the Peromyscus boylii species group from west-central Mexico have been referred to as Peromyscus boylii; however, a distinct but polymorphic karyotype (fundamental number 54–56) precludes an assignment of these specimens to currently recognized taxa. Phylogenetic analyses (parsimony, likelihood, and Bayesian) of DNA sequences indicated that samples from Durango, Mexico, formed a monophyletic clade that either was sister to P. levipes (parsimony) or to a clade containing P. beatae and P. levipes (likelihood and Bayesian). To refer these samples to P. boylii results in paraphyly and a significantly worse topology. Together, these results indicate that the samples from the Sierra Madre Occidental region of Durango and southeastern Sinaloa represent an undescribed species of Peromyscus. This taxon is described herein as a new species.

Despite previous work on the North American sigmodontine rodents, phylogenetic relationships within the neotomine–peromyscine complex remain conjectural. The debate focuses not only on the number of tribes within the group, but also on the relationships of genera within each tribe. Phylogenetic relationships of 19 species representing 13 genera of neotomine–peromyscine rodents were examined by using approximately 1,200 base pairs (bp) of exon 6 of the nuclear, protein-coding dentin matrix protein 1 gene (Dmp1). The topology obtained from the maximum likelihood analysis indicated that 4 tribes should be recognized: the Neotomini, Peromyscini, Baiomyini, and Tylomyini, with the Tylomyini sister to a rapidly radiating clade of neotomine–peromyscine–baiomyine rodents. In addition, it appears that Dmp1 is phylogenetically informative at the tribal level in North American sigmodontine rodents.

This paper describes variation at 6 microsatellite loci in 107 specimens of Ctenomys minutus from a chromosomal hybrid zone on the coastal plain of southern Brazil. Of the 56 alleles uncovered in this study, 39.2% are exclusive to alternative cytotypes or the contact populations. Clinal variation is not obvious because there are no microsatellite fixed differences among chromosomally divergent populations, but variation at Hai 2 locus is gradual across the zone. The local populations are highly differentiated and structured. The moderate estimated values of gene flow follow an isolation-by-distance model, which predicts concentration of an allele or a homozygous genotype in patches with generations of individuals with limited dispersal and mating by proximity. Analysis of populations distantly localized from the contact zone probably will provide further insights in the genetic relationship among cytotypes.

We examined the genetic structure of 5 Wyoming cougar (Puma concolor) populations surrounding the Wyoming Basin, as well as a population from southwestern Colorado. When using 9 microsatellite DNA loci, observed heterozygosity was similar among populations (H_O = 0.49–0.59) and intermediate to that of other large carnivores. Estimates of genetic structure (F_ST = 0.028, R_ST = 0.029) and number of migrants per generation (Nm) suggested high gene flow. Nm was lowest between distant populations and highest among adjacent populations. Examination of these data, plus Mantel test results of genetic versus geographic distance (P ≤ 0.01), suggested both isolation by distance and an effect of habitat matrix. Bayesian assignment to population based on individual genotypes showed that cougars in this region were best described as a single panmictic population. Total effective population size for cougars in this region ranged from 1,797 to 4,532 depending on mutation model and analytical method used. Based on measures of gene flow, extinction risk in the near future appears low. We found no support for the existence of metapopulation structure among cougars in this region.

The 4 species of phocid pinnipeds that live in pack-ice habitats of the Antarctic have been relatively isolated from infectious diseases that are prevalent in mammals elsewhere. Consequently, patterns of genetic variability at key immune system loci in these seals might be primarily related to other selective factors correlative with interspecific differences in life history, demography, and ecological niches. To test that hypothesis, we investigated nucleotide-sequence variation in a 162-base pair region of DQα exon 2 in major histocompatibility complex (MHC) class II genes of Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophaga), Ross seals (Ommatophoca rossii), and leopard seals (Hydrurga leptonyx) from the Ross Sea of Antarctica. We found substantial differences in patterns of population genetic diversity among these seals. Crabeater seals were the most diverse, with 2 DQα loci, 39 distinct alleles among 30 seals, and at least 93% observed heterozygosity. Leopard seals were the least diverse, with only 1 allele detected in 13 seals. Weddell and Ross seals had intermediate diversity, with 11 alleles in 35 Weddell seals (89% observed heterozygosity) and 2 alleles in 42 Ross seals (21% observed heterozygosity). These patterns are congruent with extant knowledge of interspecific variation in life histories, population biology, and ecological niches of these species and consistent with previously reported patterns of microsatellite genetic variability. Moreover, our findings suggest that responses to past evolutionary pressures have differed in each species and that interspecific variation in future responses to introduced infectious diseases also may vary substantially.

The degree of molar eruption and wear were used to assign individuals of the social highveld mole-rat (Cryptomys hottentotus pretoriae) from South Africa into 9 relative age classes. Reproductive animals were found to be the oldest and heaviest members of colonies. Cranial morphometric analysis of 4 geographically disparate populations in South Africa generally showed lack of sexual dimorphism in cranial characteristics, but revealed 2 distinct groupings among the 9 relative age classes. The 1st grouping comprised individuals of age classes 1–4, which were all nonreproductive animals and considered to represent a combination of juveniles and subadults. The 2nd grouping included individuals of age classes 7–9, which included reproductive animals. Individuals of age classes 5 and 6, however, were largely intermediate, with some individuals included among both the younger and older age classes, but only a few of these animals were reproductive. These groupings suggest that if age classes are visualized as demarcating sections of variable and unknown length on a hypothetical growth curve, then individuals of age classes 5 and 6 appear to fall at a point on the curve just before it begins to stabilize. These results, together with a proposed microsatellite study, have the potential to provide additional tools to improve our current understanding of social structuring within colonies of the highveld mole-rat.