Phylogenetic relationships within Geomys historically have been difficult to assess using morphometric and chromosomal data. DNA sequences from the nuclear-encoded interphotoreceptor retinoid-binding protein gene (Rbp3) and mitochondrial 12S ribosomal RNA (12S rRNA) gene were used to examine the relationships within Geomys. In addition, sequence data from Rbp3 and mitochondrial 12S rRNA gene regions were combined with DNA sequence data from the mitochondrial cytochrome-b gene (Cytb) reported in a previous study. Results from phylogenetic analyses support previously established relationships in the recognition of 4 species groups (breviceps, bursarius, personatus, and pinetis) and a minimum of 12 species. Additionally, results agree with previous studies in considering the elevation of G. pinetis mobilensis and G. breviceps sagittalis to species-level status and in reevaluating the taxonomic status of 2 additional subspecies (G. personatus davisi and G. p. maritimus).

The genus Scotophilus is composed of 15 recognized species with 7 species distributed throughout sub-Saharan Africa, 4 distributed across southern and southeastern Asia, 3 endemic to Madagascar, and 1 endemic to Reunion Island. Scotophilus is plagued with problems in species definition, and systematic relationships among members of the genus are poorly understood. We used mitochondrial DNA (mtDNA) and Y-chromosome sequence data from 11 of the 15 recognized species, which represent the most comprehensive taxonomic coverage to date, to examine phylogenetic patterns within Scotophilus. All trees have S. kuhlii from Asia as the most basal species followed by S. nux from Africa. However, S. heathii from Asia is embedded within the other African Scotophilus, indicating a complex biogeography with multiple continental exchanges. Furthermore, the Malagasy taxa are most closely related to 2 different African species, suggesting independent colonizations of Madagascar from the continental mainland. In addition, African S. dinganii did not comprise a monophyletic group but exhibited at least 2 additional cryptic species based on high levels of genetic divergence in the cyotchrome-b gene. The large-bodied S. nigrita is closely related to S. dinganii with a similar mtDNA haplotype but distinct zfy haplotype, suggesting a possible hybridization event in the most recent common ancestor that potentially represents a mitochondrial capture. Overall measures of interspecific genetic distances ranged from 4.2% to 19.2% for mtDNA data and 0.18% to 2.14% for Y-chromosome data, indicating that members of the genus Scotophilus are highly divergent from one another.

Nuclear copies of mitochondrial DNA fragments (numts) have been reported in a number of mammalian taxa. The inclusion of these numt pseudogenes within mitochondrial data sets can unknowingly compromise the integrity of phylogenetic, systematic, and biogeographic studies. Here, we evaluate 6 unique cytochrome-b numt sequences isolated in the southern red-backed vole (Myodes [formerly Clethrionomys] gapperi). Each sequence contains features characteristic of numt pseudogenes including premature stop codons, insertions–deletions (indels), frame-shift substitutions, and transposable element insertions. Mitochondrial and nuclear sequences are evolving at different rates. Molecular dating indicates that this group of mitochondrial transfers originated ∼4.6 million years ago, which predates the presumptive origin of the genus. Phylogenetic analyses of mitochondrial and nuclear sequences suggest that the numts are the result of at least 1 nuclear insertion followed by subsequent duplication events, but pairwise sequence comparisons do not support this assertion. This conflict is likely the result of incomplete numt sampling from the Myodes nuclear genome. Genome sequencing efforts will ultimately provide the data needed to fully characterize numt demography in different lineages, and we predict that numts will have phylogenetic utility as informative synapomorphies in closely related species.

The central Rocky Mountain region of North America lies at the biogeographic crossroads of the Rocky Mountains, Great Plains, and Great Basin. Here, we examine genetic patterns in an abundant, widely distributed, and ecologically important rodent species, the long-tailed vole (Microtus longicaudus), across this climatically and tectonically dynamic landscape. We examine patterns of genetic diversity in relation to the species' overall phylogeographic distribution using mitochondrial cytochrome-b sequences from modern, historic, ancient, and published samples. Our analyses reveal extensive genetic diversity in the central Rockies, a lack of population structure, and a lack of concordance between genetic and morphological subspecies distributions. Patterns of genetic variation in late-Holocene and modern populations are similar. We conclude that geographical features such as the Continental Divide, previously isolated glacial cover, and major rivers do not result in persistent genetic structure within the long-tailed vole. We also conclude that the central Rocky Mountain region is a zone of secondary contact for divergent mitochondrial lineages of the long-tailed vole.

Polar bears (Ursus maritimus) are faced with potential drastic changes to their ice habitat in the near future. Climate models predict that the ice-covered period during which bears use the sea ice to hunt seals is getting shorter, and that the ice-free season will become extended. Bears will not have enough ice time to accumulate the necessary body fat reserves they need to live off when stranded on land during summers. However, polar bears have been observed making use of several food sources while on land, although the energetic contributions of these diets to the bears' energy budget were considered to be minor. We examine mathematically whether observed diets (i.e., arctic charr [Salvelinus alpinus], ringed seal [Pusa hispida] blubber, and berry diets) can contribute sufficient energy to offset the daily body mass loss. We then estimate the amount or mass of the diet that must be consumed to achieve a balanced daily energy loss, and whether this is possible, given specific constraints on feeding. The analysis indicated that it is possible for polar bears to maintain their body mass while on shore by feeding on arctic charr and seal blubber. Polar bears of body masses up to 280 kg could gain sufficient energy from blueberries to match the daily energy loss. The question that arises is how many bears of a population would resort to such strategies? To better understand how polar bears will adapt to a warming climate, we recommend continued examination of polar bear diets in the field, and controlled feeding trials with captive polar bears.

We investigated the effects of fluctuating prey numbers on the foraging strategies and potential mechanisms for coexistence of 2 sympatric predators, coyotes (Canis latrans) and red foxes (Vulpes vulpes), in a heterogeneous environment in northeastern Illinois. We quantified the availability of mammalian and avian prey across different habitats, analyzed scats collected along standardized routes for occurrence of prey items, and estimated the number and biomass of vertebrate prey consumed. Abundances of the most frequently consumed prey (voles, rabbits, and mice) differed significantly over time, especially in relation to an ice storm that occurred during the study. Coyotes and red foxes tended to select voles and rabbits in number, rabbits in biomass, and incorporated greater numbers and biomass of other prey such as deer, pheasants, and sciurids after the ice storm. Log-linear analyses indicated that both coyotes and red foxes exhibited switching behavior, with differential shifts among the number and biomass of alternative prey they consumed. Hence, foraging strategies of coyotes and red foxes appeared to be a combination of prey selectivity and switching behavior. Our study suggests that competition between coyotes and red foxes for similar primary prey species and limited environments to exploit at the urban–rural interface may contribute to displacement of red foxes by coyotes.

We used logistic regression to examine factors that affected the spatial distribution of sign (scrapes, feces, footprints, spray or scent marks, and rubbing sites) in a newly reestablished population of snow leopards (Uncia uncia) in Sagarmatha (Mount Everest) National Park, Nepal. Our results indicate that terrain and human activity were the most important factors determining the spatial distribution of leopard activity, whereas presence of their major prey species (Himalayan tahr [Hemitragus jemlahicus]) had only a moderate effect. This suggests that localities at which these animals are active represent a trade-off between suitable habitat and avoidance of potential risk from anthropogenic origins. However, the influence of prey presence was likely underestimated because of the methodology used, and likely weighed in the trade-off as well.

We used extensive camera-trap surveys to study interindividual interactions among individually recognizable jaguars (Panthera onca) and plain-colored pumas (Puma concolor). Timed location data from a network of 119 trap stations in the Cockscomb Basin of Belize provide the 1st evidence of interspecific avoidance calibrated against intraspecific interactions among jaguars. Camera trapping has advantages over radiotelemetry in its potential to provide data on the complete array of individuals within the study area. The 23 individually identified male jaguars showed high levels of overlap in ranges, with up to 5 different males captured at the same location in the same month. Low levels of avoidance between individuals and a high flux of individuals contributed to low consistency in home-range ownership over the long term (3 months to 2 years). Jaguars and pumas had similar nocturnal activity schedules. Both species used similar habitats within the Cockscomb Basin, indicated by a high correlation in capture rates per location between species. Apart from their overall spatial similarities, jaguars and pumas avoided using the same location at the same time. This interspecific segregation was detectable over and above the spatial and temporal segregation of individual jaguars.

Twinning in natural pinniped populations is often inferred from observations of suckling behavior, but this approach has been criticized because nonfilial nursing occurs at high frequencies in many seal species. Consequently, we used 9 highly polymorphic microsatellite markers to examine the parentage of 11 putative pairs of twins in Antarctic fur seals (Arctocephalus gazella) breeding at Bird Island, South Georgia. Only 3 pairs (27%) were found to be genuine twins, indicating that suckling observations are an unreliable means of identifying twins in this species. All of the twins were female; 1 pair was monozygotic and the other 2 were dizygotic. Using a strict exclusion approach, paternity was assigned to the monozygotic but not the dizygotic twins. However, likelihood tests revealed that, of the latter, 1 pair was significantly more likely to be full siblings against the null of half sibship suggesting shared paternity, whereas the other pair was more likely to be half siblings against the null of full sibship indicating probable multiple paternity. Our results provide novel insights into the reproductive ecology of fur seals and also support an earlier study showing that molecular genetic analysis can provide an effective means of validating field observations of pinniped twins.

Blubber is a critical component of thermoregulation for marine mammals, particularly for cetaceans. However, the cost of overcoming blubber's buoyant force during descent could constrain blubber deposition. One- to 12-year-old healthy, free-ranging common bottlenose dolphins (Tursiops truncatus) were studied in Sarasota Bay, Florida, during summer (mean water temperature: 29.7°C ± 0.1 SE) and winter (mean water temperature: 19.2 ± 0.4°C) to examine ontogenetic and seasonal trends in morphology and blubber deposition. Surface-area-to-volume ratio decreased significantly with age. During summer, yearlings had significantly thicker blubber than 2- to 12-year-old animals but this difference diminished by winter because blubber deposition in response to the colder water temperature was smaller in yearlings (2-mm increase) compared to 2- to 12-year-old animals (3- to 6-mm increase). During summer, buoyancy was highest in yearlings (6.24 N ± 0.41 SE), compared to a buoyant force of −0.98 ± 0.90 N (neutrally buoyant) for 12-year-old animals. Conversely, all dolphins converged upon a similar buoyant force (8.01 ± 0.56 N) in winter. The elevated buoyancy of yearlings in summer presumably limits seasonal blubber adjustments, because all yearlings (regardless of season) converged upon a similar calculated mass-specific cost of descent that was greater than all other age classes. Balancing energetic demands of thermoregulation and locomotion may limit the flexibility of yearlings to adjust blubber deposition in response to fluctuating water temperatures.

We examined the possibility that parameters of bottlenose dolphin signature whistles may serve as indicators of stress. Bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida, were recorded during brief capture–release events, which are potentially a source of short-term stress to these dolphins, although no effects of chronic or long-term stress have been observed over the 37 -year duration of the research. Whistles recorded during both brief capture–release and undisturbed, free-ranging conditions were examined to determine whether whistle parameters differ during capture–release versus undisturbed conditions; at the beginning of a capture–release session versus at the end of a session; during an individual's 1st capture–release session versus later capture–release sessions; and when a mother is caught and released with a dependent calf versus without a dependent calf (i.e., she has no dependent calf at the time of capture–release). We examined a variety of acoustic parameters, including whistle rate, number of loops (repetitive elements), maximum and minimum frequency, and loop, interloop, and whistle duration. We found that whistle rate and number of loops were greater during brief capture–release events than during undisturbed conditions; number of loops decreased and loop duration increased over the duration of a capture–release session; whistle rates decreased with number of capture–release sessions; and females caught and released with dependent calves produced whistles with higher maximum frequencies and shorter interloop intervals than when they did not have dependent calves. Thus, whistles appear to have potential as noninvasive indicators of stress in bottlenose dolphins. Further research is warranted in this area, for example by correlating physiological indices to whistle rates under varying levels of stress. Reliable, noninvasive correlates of stress could be used to monitor dolphins in a variety of circumstances, such as during exposure to anthropogenic noise.

Identifying maternal effects on offspring is critical to interpreting population dynamics, but the duration of maternal effects and which life-history traits they influence is not well understood. We quantified growth and development of male white-tailed deer (Odocoileus virginianus) originating from the Black Hills in southwestern South Dakota and from eastern South Dakota in a controlled environment with high-quality nutrition. Despite being in good nutritional condition, males from the Black Hills ceased rapid growth 41 days earlier, were 29% smaller at asymptotic body mass, and grew significantly smaller antlers than males from eastern South Dakota. Females from eastern South Dakota were 14.9 kg larger than females from the Black Hills, yet birth mass of male offspring was similar for females from the 2 regions. Male offspring of 1st-generation deer from the Black Hills attained a 30% larger asymptotic body mass and grew significantly larger antlers than their sires. Body mass and antler size of 2nd-generation males of Black Hills origin approached that of 1st-generation males from eastern South Dakota at maturity. Suppression in growth of 1st-generation males of the Black Hills and increased growth by their offspring supported an influence of maternal and grandmaternal condition during gestation on subsequent growth of offspring and highlighted the significance of nutrition during gestation. These intergenerational effects indicate that measures of animal condition and population performance might reflect past rather than current conditions, and illustrate the potential for time lags in responses of populations to improved environmental conditions.

We investigated age-specific variation in male yearly breeding success (YBS) using genetic estimates obtained from 2 populations of a territorial ungulate, the European roe deer (Capreolus capreolus). YBS in both populations was markedly age-structured, with 3 distinct stages, supporting the dome-shaped pattern of variation commonly reported for age-dependent variation in life-history traits of ungulates. YBS was low at 2 years of age, peaked at 3–8 years of age, and tended to decline afterwards (senescence). Most males successfully reproduced for the 1st time at 3 years of age, which is well after their physiological maturity. The few successful young males (i.e., 2 year olds) were likely fast-growing individuals that could successfully hold a territory. The high variance in YBS and antler size for old males at Bogesund, Sweden, suggests that only some males of this age class are able to maintain large antlers and, hence, retain their territories.

We investigated the social organization of wild boars (Sus scrofa) using genetic and spatial data from a study population in Tuscany, Italy. In total, 120 wild boars of different sexes and age classes were captured and monitored from 2002 to 2006. All of them were genetically analyzed by using 10 polymorphic microsatellites (H_E  =  0.693, k  =  6.6) and a matrix of pairwise relatedness was calculated. In addition, a reference sample of fully related individuals was created by genotyping 11 adult females and their fetuses (n  =  56). Spatial data were gathered for 65 animals that had been fitted with either radiocollars or ear transmitters. Sixteen social units were identified by capture data and confirmed by observations and telemetry. A correlation between interindividual spatial distance and relatedness was observed only in summer–early autumn and seemed to be associated to the presence of piglets. The prediction of matrilinearity in wild boar social units was not confirmed, because a low degree of relatedness among boars was observed within groups. Aggregations of unrelated adult females (with their litters) were detected in the study population. The high turnover in the population due to human-caused mortality seems to be the main factor responsible for this altered social structure. Accordingly, we suggest that the observed social organization would result from grouping of unrelated survivors that is promoted by the presence of wolves in the area.

Use of the aquatic environment by hippopotami (Hippopotamus amphibius) allows locomotive styles impossible to achieve on land by such heavy animals. Videos of the underwater locomotion of 2 hippopotami were analyzed frame by frame. Average horizontal velocity underwater was 0.47 m/s. Hippopotami used a gait underwater that was similar to a gallop with extended unsupported intervals. Ground contact time decreased with increasing horizontal velocity, vertical displacement during the unsupported intervals increased with an increase in ground contact time, and time between consecutive footfalls decreased with an increase in horizontal velocity. Hippopotami use an unstable gait underwater, which is facilitated by the increased buoyancy of water. Despite restrictions to movement on land due to its massive weight, locomotion of the hippopotamus underwater is analogous to movement in a microgravity environment.

We used regression trees to assess seasonal relationships between vital rates (survival and reproduction) and a suite of environmental variables for hispid cotton rats (Sigmodon hispidus) and prairie voles (Microtus ochrogaster). We found only 2 relationships between vital rates and environmental variables for M. ochrogaster, whereas we found relationships in all seasons for S. hispidus. The majority of recovered regression trees contained multiple variables, indicating that the vital rates of S. hispidus were affected by interactions among environmental correlates. Vital rates of S. hispidus were affected most by precipitation, temperature, and snowfall; but the direction of effects of these environmental variables was not consistent among seasons. Our analyses indicate that populations of M. ochrogaster in northeastern Kansas are relatively insensitive to environmental variability, whereas survival and reproduction in S. hispidus are influenced by the environment throughout the year.

Olympic marmots (Marmota olympus) are large, burrowing rodents inhabiting scattered subalpine meadows on the Olympic Peninsula, Washington. Recently, the population has declined and become increasingly fragmented. The ability of Olympic marmots to recolonize abandoned habitat and to maintain gene flow among extant populations will depend on the number and success of dispersers and the distances that they travel. We monitored 84 radiotagged Olympic marmots to determine dispersal rates, distances, and success. Contrary to previous observations, 3-year-olds were most likely to disperse, although some 2-year-olds and even some older animals, particularly males, moved as well. Of marmots known to be still on their natal home range in the spring of a given year, 16% of 2-year-old males, 50% of 3-year-old males, 17% of 2-year-old females, and 29% of 3-year-old females subsequently dispersed. Dispersal rates for 3-year-olds were slightly lower when all animals were included in the analysis regardless of whether their dispersal history was known. Males dispersed farther than females (median  =  984 m, n  =  14 versus median  =  267 m, n  = 13) and 69% of females settled within 500 m of their original home range. If the observed dispersal patterns are representative of range-wide patterns and if Olympic marmot densities remain low, successful dispersal may be too infrequent to sustain reliable recolonization of vacant habitats or even genetic or demographic rescue of isolated marmot groups.

Examination of extensive data from field and laboratory studies indicates that prairie voles (Microtus ochrogaster) are socially monogamous and form pair-bonds. We used grid-trapping data from replicate populations of prairie voles living in 0.1-ha small mammal enclosures at 2 different initial densities to examine the extent to which opposite-sex adults captured together in the same live trap reflected social associations established from nest-use patterns and the probability that the pair produced offspring. Females classified as a resident at a nest that also included at least 1 resident male (male–female pairs or groups) were significantly more likely to be trapped with a male from the same social unit (64%) rather than a male from another social unit or a male wanderer (an animal not considered a resident at any nest site). On the other hand, females residing at a nest with no resident males were caught with wandering males significantly more often (84%) than with resident males from another nest. Finally, female wanderers were significantly more likely to be trapped with male wanderers (75%) than with resident males. A genetic analysis of parentage revealed that females were significantly more likely to have produced offspring with the male with which they were caught most frequently (80% of females) than to not breed with these males. None of these findings were influenced by density. Overall, the multiple-capture data were consistent with social monogamy and the relative frequency of male–female multiple captures were predictive of the likelihood of mating. However, although most females residing at nests with resident males bred with these males (84%), a similar percentage of these females also bred with at least 1 male that never resided in the same social unit as the female, suggesting that prairie voles are not genetically monogamous throughout their lives.

Space use in mammals may vary between the sexes. This may reflect demographic or reproductive differences between the sexes as well as different responses to changes in resource availability. We present the results of a 2-year study on the spatial organization of the yellow-necked mouse (Apodemus flavicollis) in a beech woodland in the eastern Italian Alps. We used radiotelemetry to monitor the movements of 64 mice during the breeding season (i.e., from July to October) in 2005 (high population density) and 2006 (low population density). In both years, home ranges of males were significantly larger than those of females and overlapped with the areas occupied by several individuals of both sexes. Females monopolized core areas and never shared burrows with other females—suggesting intrasexual territoriality—although their home ranges overlapped those of several males. Space use changed seasonally and among years, suggesting a relationship with resource abundance and distribution. Females exhibited reduced spatial exclusivity and larger home ranges during lower food availability; males varied their spatial distribution accordingly by also expanding their home ranges. After a decrease in habitat quality, we observed substantial and abrupt adult dispersal by both sexes. In sum, females varied their spatial and social relationships in response to environmental conditions, whereas males appeared to vary patterns of space use in response to females.

Scotinomys xerampelinus, the long-tailed singing mouse, is diurnal and insectivorous, and exhibits a complex and unique calling behavior that is audible to humans. Little is known about the social structure of this species. We used livetrapping and radiotracking to investigate the spatial organization of a wild Panamanian population of long-tailed singing mice. We observed exclusive space use among females but not among males. For both males and females, individual home ranges (85% minimum convex polygons) typically overlapped with >1 animal of the opposite sex. No significant differences in body mass, hind-foot length, or home-range size (area) were found between males and females. Most individuals in the population nested alone. Patterns of space use and sexual dimorphism are frequently used to infer species' mating systems. Our results, in particular the tendency for individual home ranges to overlap with multiple potential reproductive partners, are most consistent with a promiscuous mating system.

We studied maternal, paternal, and alloparental care in striped mice (Rhabdomys pumilio), which nest and breed communally in the succulent karoo, South Africa. A total of 18 triads, each consisting of 2 adult female littermates and an unfamiliar adult male, were set up under natural weather conditions. We expected that relationships within captive triads that breed communally would be egalitarian, and that all individuals would participate in the rearing of offspring, but we assumed that the degree of caregiving behavior would vary between mothers, fathers, and alloparents, because individuals obtain different fitness benefits. Social interactions in the triads were predominantly amicable and in the majority of triads, both females produced litters in a communal nest. All 3 adults in a triad participated in care of the offspring, with mothers spending 43%, fathers 26%, and alloparents 24% of observations in caregiving activities. Our results indicate that sisters can form stable cooperative relationships, but members of a communal nest allocate their caregiving to individual offspring according to potential trade-offs between direct and indirect fitness benefits. Large amounts of paternal care can occur in a polygynous species, which contrasts with the common belief that paternal care is a characteristic of monogamy.

We investigated species composition of the bat assemblage in continuous forest and natural forest islands in a savanna ecosystem in northern Bolivia. We captured 396 bats of 24 species. Five species accounted for almost 70% of the captures: Sturnira lilium, Artibeus obscurus, Carollia brevicauda, Carollia perspicillata, and Artibeus lituratus. Species composition of the bat assemblage differed between continuous forest and forest islands; Artibeus jamaicensis and S. lilium were captured more often in islands, whereas Platyrrhinus helleri and Mesophylla macconnelli were more common in the continuous forest. The distribution of species over the forest islands and the continuous forest revealed a nested distribution pattern, with the continuous forest having the highest number of species, and the smallest island having the fewest species. However, bats were almost 5-fold more abundant in forest islands than in continuous forest. Examination of recapture data indicated movements of bats among forest islands and between islands and continuous forest. Our results suggest that bat populations, especially in the fruit-eating guild, can persist in a naturally fragmented landscape.

Stable hydrogen isotopes (δDs) in metabolically inert tissues such as feathers and hair provide a set of endogenous markers that may be useful for establishing migratory connectivity in animals. We tested the assumption of a clear relationship between δD values of growing-season–weighted average precipitation (δD_p) derived from 2 geographic information system (GIS) models or latitude (LAT) and δD values in bat hair (δD_h), and examined intra- and interspecific variation in δD_h of 4 bat species in the eastern United States. We analyzed 251 hair samples from 1 long-distance migrant (eastern red bat [Lasiurus borealis]) and 3 regional migrants (Indiana bat [Myotis sodalis], northern long-eared bat [M. septentrionalis], and little brown bat [M. lucifugus]) captured during the reproductive period (pregnancy and lactation) when bats are resident. LAT explained more of the variation in δD_h than δD_p derived from either of the GIS-based models, although 1 model of δD_p performed better for some species. We found significant intraspecific differences in the relationships between δD_h and LAT and between δD_h and estimates of δD_p derived from Bowen et al. (δD_pB) for L. borealis, and significant variation in the regression equations of δD_h and LAT and δD_h and δD_p among species for adult females and adult males. Stable hydrogen isotope analysis may be a valuable tool for studying migratory connectivity in bats, but significant intra- and interspecific variation in δD_h values suggests that pooling across sex and age categories and use of surrogate species should be avoided.

The little red kaluta (Dasykaluta rosamondae) is a small, insectivorous–carnivorous dasyurid marsupial found in arid spinifex grasslands of northwestern Australia. Kalutas resemble other dasyurids in many aspects of their physiology. Body temperature (T_b; 33.5°C; 1.5°C lower than predicted), wet thermal conductance (1.6 J g⁻¹ h⁻¹ °C⁻¹; 91% of predicted), and dry thermal conductance (1.22 J g⁻¹ h⁻¹ °C⁻¹; 55% of predicted) are not significantly different from allometric predictions for marsupials in the thermoneutral zone (26–33°C). A significantly lower-than-expected basal metabolic rate (0.55 ml O₂ g⁻¹ h⁻¹; 58% of allometric prediction) and evaporative water loss (1.11 mg g⁻¹ h⁻¹; 39% of predicted) can be attributed to the combined effect of low T_b and phylogeny. Physiological adaptation to aridity is further reflected by a substantially smaller body mass (35 g) than predicted by phylogeny (200 g), a thermolabile T_b and use of torpor, which confer significant energy and water savings, and a high point of relative water economy (16.1°C).

Seasonal acclimatization in high-latitude endotherms may involve increases or reductions in body size and metabolic rate to, respectively, augment thermoregulatory capacity or reduce energy requirements. We investigated seasonal acclimatization in a northern population of wild snowshoe hares (Lepus americanus) that is exposed to low food availability and extremely cold temperatures in winter. Snowshoe hares were livetrapped and transported to a nearby mobile laboratory. Hares were placed in a metabolic chamber and oxygen consumption was measured for 55 min at each of the following temperatures: 10°C, 0°C, −10°C, −15°C, and −20°C. Hair length and density were measured on a sample of collected hares. Snowshoe hares maintained similar body mass and body temperature between the seasons, but average resting metabolic rate and thermal conductance were, respectively, 20% and 32% lower in winter than in autumn. The lower critical temperature was −10°C to −15°C in winter and 0°C to −10°C in autumn. Guard hairs were 36% longer and 148% denser in winter than autumn, whereas downy hairs were the same length but 128% denser in winter than autumn. Collectively, these results suggest that resource constraints associated with a herbivorous diet in regions and seasons of poor forage quality favors an energetically conservative approach to winter acclimatization.

The analysis of orthodentine microwear has recently been established as a proxy for diet in extant and fossil xenarthrans (sloths, armadillos, and their extinct relatives). Previous analyses have relied on standardized comparison of sampling locations between taxa in order to statistically correlate microwear on xenarthran teeth with primary diet; variation in orthodentine microwear across the toothrow and its potential effect on dietary classification in xenarthrans remains unexplored. This study is the 1st to examine intertooth variation of microwear features in extant xenarthrans to test the necessity of standardized tooth comparison in orthodentine microwear analysis of paleodiet in fossil taxa. Statistical mean correlation tests were used to compare microwear variables between different sampling locations in a series of upper and lower teeth in 4 extant xenarthran species (Bradypus tridactylus [pale-throated three-toed sloth], Choloepus didactylus [Linnaeus' two-toed sloth], Dasypus novemcinctus [nine-banded armadillo], and Euphractus sexcinctus [six-banded armadillo]) and showed that microwear distribution between sampling locations is more conserved in three-toed sloths relative to two-toed sloths and armadillos. Significant variation in the latter groups may stem from uneven distribution of bite-force on the dentition in long-faced animals (two-toed sloths and armadillos) relative to short-faced animals (three-toed sloths), although food texture and intraspecific variation in diet may play a role as well. Based on results from extant taxa, standardized tooth comparison is required for analysis of paleodiet in glyptodonts and pampatheres and also is recommended for ground sloths in future studies of microwear.