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Molting is an evolutionarily ancient trait in which the outermost layer of an organism is replenished, usually according to a regular circannual rhythm. It is a metabolically costly process and, in vertebrates, is generally timed around other energetically demanding events such as reproduction and migration. In mammals, molting involves replacement of the fur coat—one of the most distinct innovations of the mammalian lineage. Despite the obvious importance of hair to mammalian fitness, our knowledge of hair growth cycles, circannual molting patterns, and hair structure remains largely restricted to marine and domesticated mammals, and our ability to identify explicit adaptive advantages of molting strategies in any mammal is therefore limited. In this review, we summarize what is known of these topics in wild, terrestrial mammals with a particular emphasis on marmots (Marmotaspp.). Marmots are the largest extant ground squirrels and are well adapted to seasonally cold environments. Molting may be particularly relevant to fitness in marmots given the presumed importance of a healthy, insulative coat for metabolic efficiency in cold environments. Moreover, marmots hibernate for 7 to 8 months each year, meaning the annual molt and all other energetically demanding life-history events (such as parturition, lactation, fat accumulation, and dispersal) are constrained to an active period of only 4 to 5 months. Because the energetics of hibernation, fat accumulation, reproduction, and social behavior are already well studied, examining how molt is timed with respect to other important events and how it is influenced by local conditions may inform how molting is prioritized and how molting strategies evolve under specific selective pressures.Hair has only evolved once in the history of life, and it is thought to be one of the most important adaptations underlying the successful radiation of mammals. But the adaptive utility of hair is closely intertwined with the process of molting—the metabolically expensive, carefully timed, cyclical replenishment of the pelage. Here we review what is known (and unknown) of the mammalian molt, while emphasizing that molting strategy is a phenotypic trait that can and has evolved over time. We use marmots (genus Marmota) as an example to demonstrate how the adaptive value of different molting strategies might be evaluated, as little research has been carried out on this topic in mammals relative to birds.

Shifts in mean body size coinciding with environmental change are well documented across animal species and populations, serving as a widespread and complex indicator of climate-change response. In mammal research, identifying and disentangling the potential drivers of these trends (e.g., thermoregulation, resource availability) is hindered by treating adult size as fixed, ignoring morphological changes that occur throughout life in many species. However, observed population-level size trends may reflect underlying shifts in age structure (i.e., change in the proportion of older, potentially larger individuals in the population). Here, we assessed the role of age structure by explicitly evaluating age as a contributor to temporal variation in skull size (a proxy for body size) in 2 carnivorans, Canadian Lynx (Lynx canadensis) and American Marten (Martes americana). Using a series of linear and nonlinear models, we tested age in years (determined by cementum-layer analysis) as a predictor of skull size alongside other factors previously proposed to be important drivers of body-size trends, including population density for lynx and growing season conditions for martens. In both species, age was a significant predictor of skull size indicating a rapid year-to-year increase in young adult size that diminished in later adulthood. However, temporal shifts in age structure alone did not explain the observed changes in size over time, indicating that age structure acts in concert with other as-yet unidentified factors to drive body-size change. By explicitly evaluating the role of age, we can both refine models of temporal body-size trends and gain insights into size change as a signal of underlying demographic shifts—such as age-specific survivorship—providing a more holistic understanding of how mammals are responding to climate change.Many factors influence mammal body-size trends, but the role of population age structure remains largely unknown. We reveal skull-size increases well into adulthood and show that accounting for age structure can improve our understanding of body-size responses to climate change.

Mammals are predicted to vary in body size following Bergmann’s rule, with individuals found at higher latitudes in colder temperatures being larger in size compared to conspecifics occurring at lower latitudes in warmer temperatures. Body size is similarly expected to vary temporally, with a decrease in size through time due to recent climate warming. While Bergmann’s rule is well-supported in mammals, there is increasing evidence of exceptions to the rule. Here, we present patterns of size variation in 17 North American mammal species using five morphological traits (condylobasal skull length, skull width, maxillary toothrow length, body weight, and head-and-body length) to determine if size varies predictably for each species in space and time. We found little support for a widespread Bergmannian pattern for these species at a broad spatial scale (across North America) and a contemporary temporal scale (the past 120 years). The effects of latitude or year on each trait were highly variable with three types of responses: an increase, a decrease, or no change in size across space or through time. Spatial size trends were detected more often than temporal size trends, as the temperature range was significantly larger in space than through time. Body weight (the most variable trait) and head-and-body length were more likely to conform to Bergmann’s rule than craniodental measurements. We did not detect any changes in size variability with latitude, and our study species either increased or decreased in size variability over time. Our findings demonstrate that size variation in mammals is highly context-dependent. As such, caution is needed when using rules of body size variation to predict the future response of species to climate warning while valid in theory, it is likely too simplistic of an approach.We found little support for either spatial or temporal patterns of body size variation consistent with Bergmann’s rule across morphological traits in multiple species of North American mammals over the past 120 years.

The Lesser Treeshrew, Tupaia minorGünther, 1876, is a small mammal from Southeast Asia with four currently recognized subspecies: T. m. minorfrom Borneo; T. m. malaccanafrom the Malay Peninsula; T. m. humeralisfrom Sumatra; and T. m. sincepisfrom Singkep Island and Lingga Island. A fifth subspecies, T. m. caedis, was previously synonymized with T. m. minor; it was thought to occur in northern Borneo and on the nearby islands of Banggi and Balambangan. These subspecies were originally differentiated based on pelage color, a plastic feature that has proven to be an unreliable indicator of taxonomic boundaries in treeshrews and other mammals. To explore infraspecific variation among T. minorpopulations across the Malay Peninsula, Borneo, Sumatra, and smaller islands, we conducted multivariate analyses of morphometric data collected from the hands and skulls of museum specimens. Principal component and discriminant function analyses reveal limited differentiation in manus and skull proportions among populations of T. minorfrom different islands. We find no morphometric support for the recognition of the four allopatric subspecies and no support for the recognition of T. m. caedisas a separate subspecies on Borneo.

While museum voucher specimens continue to be the standard for species identifications, biodiversity data are increasingly represented by photographic records from camera traps and amateur naturalists. Some species are easily recognized in these pictures, others are impossible to distinguish. Here we quantify the extent to which 335 terrestrial nonvolant North American mammals can be identified in typical photographs, with and without considering species range maps. We evaluated all pairwise comparisons of species and judged, based on professional opinion, whether they are visually distinguishable in typical pictures from camera traps or the iNaturalist crowdsourced platform on a 4-point scale: (1) always, (2) usually, (3) rarely, or (4) never. Most (96.5%) of the 55,944 pairwise comparisons were ranked as always or usually distinguishable in a photograph, leaving exactly 2,000 pairs of species that can rarely or never be distinguished from typical pictures, primarily within clades such as shrews and small-bodied rodents. Accounting for a species geographic range eliminates many problematic comparisons, such that the average number of difficult or impossible-to-distinguish species pairs from any location was 7.3 when considering all species, or 0.37 when considering only those typically surveyed with camera traps. The greatest diversity of difficult-to-distinguish species was in Arizona and New Mexico, with 57 difficult pairs of species, suggesting the problem scales with overall species diversity. Our results show which species are most readily differentiated by photographic data and which taxa should be identified only to higher taxonomic levels (e.g., genus). Our results are relevant to ecologists, as well as those using artificial intelligence to identify species in photographs, but also serve as a reminder that continued study of mammals through museum vouchers is critical since it is the only way to accurately identify many smaller species, provides a wealth of data unattainable from photographs, and constrains photographic records via accurate range maps. Ongoing specimen voucher collection, in addition to photographs, will become even more important as species ranges change, and photographic evidence alone will not be sufficient to document these dynamics for many species.

The Large Treeshrew, Tupaia tanaRaffles, 1821, is a small mammal (~205 g) from Southeast Asia with a complicated taxonomic history. Currently, 15 subspecies are recognized from Borneo, Sumatra, and smaller islands, and many were originally differentiated based on minor pelage differences and small sample sizes. We explored intraspecific variation in T. tanausing quantitative osteological data obtained from the hands and skulls of museum specimens. Multivariate analyses reveal extensive overlap among T. tanapopulations in morphospace, indicating that the majority of currently recognized subspecies are not morphometrically distinct. In contrast, the separation between Bornean and Sumatran populations of T. tanais sufficient to recognize them as different subspecies. Comparisons of Bornean specimens to those on small, offshore islands reveal that the latter average smaller body size. This pattern is inconsistent with Foster’s island rule, which predicts that island populations of small mammals (< 5 kg) will average larger body size relative to mainland forms. A similar lack of support for ecogeographic rules has been noted in T. glis(Diard, 1820), suggesting that these “rules” are poor predictors of geographic variation in treeshrews.

Age is a basic demographic characteristic vital to studies of mammalian social organization, population dynamics, and behavior. To eliminate potentially confounding ontogenetic variation, morphological comparisons among populations of mammals typically are limited to mature individuals (i.e., those assumed to have ceased most somatic growth). In our morphometric studies of treeshrews (Scandentia), adult individuals are defined by the presence of fully erupted permanent dentition, a common criterion in specimen-based mammalogy. In a number of cases, however, we have had poorly sampled populations of interest in which there were potentially useful specimens that could not be included in samples because they lacked associated skulls. Such specimens typically are associated with external body and weight measurements recorded by the original collectors, and we sought to determine whether these data could be used successfully as a proxy for age or at least to establish maturity. We analyzed four traditional external dimensions (head-and-body length, tail length, hind foot length, and ear length) and weight associated with 103 specimens from two allopatric populations of the Lesser Treeshrew (Tupaia minorGünther, 1876) from Peninsular Malaysia and from Borneo, which we treated as separate samples (populations). Individuals were assigned to one of eight age categories based on dental eruption stage, and measurements were compared among groups. In general, mean sizes of infants and subadults were smaller than those of adults, but the majority of subadults fell within the range of variation of adults. The large overlap among infants, subadults, and adults in external measurements and weight indicates that such measures are poor proxies for age in this species, probably for treeshrews in general, and possibly for other small mammals. This has significant implications for any investigation wherein relative age of individuals in a given population is an important consideration.

Morphometric analyses of the manus skeleton have proven useful in understanding species limits and morphological divergence among tupaiid treeshrews (Scandentia: Tupaiidae). Specimens in these studies are typically limited to mature individuals with fully erupted permanent dentition, which eliminates potentially confounding variation attributable to age, but also can exclude rare taxa and small island populations that are poorly represented in systematic collections. To determine the real limits associated with including immature animals in such studies, we used multivariate analyses to study sexual and age variation of the manus skeleton in two allopatric populations of the Lesser Treeshrew (Tupaia minorGünther, 1876) from the Malay Peninsula and from Borneo that we treated as separate samples. Individuals were aged using dental eruption of the permanent dentition. We also recorded the degree of epiphyseal fusion of the bones of the manus based on x-rays of study skins. We then tested our ability to distinguish the two populations using a series of discriminant function analyses of hand measurements from samples that included varying proportions of immature individuals and adults. We found no evidence of sexual dimorphism in hand proportions, permitting us to combine females and males in our samples. Epiphyseal fusion of the metacarpals and phalanges typically occurs by the time the third molars have completely erupted, and fusion of the distal epiphyses of the radius and ulna typically occurs by the time the permanent fourth premolars are in place. There is occasional asynchrony between dental age and epiphyseal fusion. In both populations, the hands of most infants and subadults provide morphometric values within the range of variation of adults, although they are typically distributed in the lower part of the adult range and have the potential to bias the sample toward lower mean size. The inclusion of infants and subadults when attempting to discriminate between two taxa generally results in lower rates of correct classifications, although the rates increase as the sample of immature individuals is limited to older subadults. As a general rule, we recommend that specimens of infants and subadults continue to be excluded from analyses when exploring taxonomic boundaries among treeshrews. In cases of extremely small sample sizes of adults, however, older subadults—in which the permanent third premolars are erupting or in place—can be used with appropriate caution.

Treeshrews (order Scandentia) comprise 2 families of squirrel-sized terrestrial, arboreal, and scansorial mammals distributed throughout much of tropical South and Southeast Asia. The last comprehensive taxonomic revision of treeshrews was published in 1913, and a well-supported phylogeny clarifying relationships among all currently recognized extant species within the order has only recently been published. Within the family Tupaiidae, 2 widely distributed species, the northern treeshrew, Tupaia belangeri(Wagner, 1841), and the common treeshrew, T. glis(Diard, 1820), represent a particularly vexing taxonomic complex. These 2 species are currently distinguished primarily based on their respective distributions north and south of the Isthmus of Kra on the Malay Peninsula and on their different mammae counts. This problematic species complex includes 54 published synonyms, many of which represent putative island endemics. The widespread T. glisand T. belangericollectively comprise a monophyletic assemblage representing the sister lineage to a clade composed of the golden-bellied treeshrew, T. chrysogasterMiller, 1903 (Mentawai Islands), and the long-footed treeshrew, T. longipes(Thomas, 1893) (Borneo). As part of a morphological investigation of the T. glis-T. belangericomplex, we studied the proportions of hand bones, which have previously been shown to be useful in discriminating species of soricids (true shrews). We measured 38 variables from digital X-ray images of 148 museum study skins representing several subspecies of T. glis, T. belangeri, T. chrysogaster, and T. longipesand analyzed these data using principal components and cluster analyses. Manus proportions among these 4 species readily distinguish them, particularly in the cases of T. chrysogasterand T. longipes. We then tested the distinctiveness of several of the populations comprising T. glisand T. longipes. T. longipes longipesand T. l. salatanaLyon, 1913, are distinguishable from each other, and populations of T. “glis”from Bangka Island and Sumatra are distinct from those on the Malay Peninsula, supporting the recognition of T. salatana, T. discolorLyon, 1906, and T. ferrugineaRaffles, 1821 as distinct species in Indonesia. These relatively small, potentially vulnerable treeshrew populations occur in the Sundaland biodiversity hotspot and will require additional study to determine their appropriate conservation status.

In the February 2001 issue of the Journal of Zoology a paper was published by Robert Timm and John Brandt (2001) that provided a new identification for two bovid frontlets held in the Kansas Natural History Museum. The frontlets had been collected in 1929 from Suoi Kiet, Binh Tuy Province in Vietnam and had been previously identified as kouprey Bos sauveli. Timm and Brandt re-identified the two frontlets as adult male and female representatives of the recently described spiral-horned ox Pseudonovibos spiralis Peter & Feiler, 1994.

Scansoriality (climbing) allows access to valuable resources in the arboreal niche and is widespread among mammals, yet little is known about how it originates from obligate terrestriality. The northern red-backed vole (Myodes rutilus) is a small, Holarctic rodent long presumed to be strictly terrestrial, yet 3 of its congeners (M. gapperi, M. glareolus, and M. californicus) have been observed climbing in trees. We conducted paired arboreal and ground trapping surveys in interior Alaska to investigate anecdotal accounts of tree-climbing behavior in M. rutilus. Results indicate that they readily climb up to 2 m above ground in trees of their own volition, a phenomenon heretofore undocumented in the literature. Camera trap videos show M. rutilus exhibiting behavior and dexterity—such as terminal branch arboreal quadrupedalism and head-first descent mediated by hindfoot rotation—generally associated with more arboreal species. Northern red-backed voles may therefore provide a new perspective on early stages of scansoriality in small-bodied mammals.

Climate change resulting in a reduction of alpine habitat is believed to pose a considerable risk to alpine-dependent species, including many marmots. Hoary marmots (Marmota caligata) range throughout much of the mountainous Pacific Northwest (PNW) and Rocky Mountains while the closely related Olympic and Vancouver Island marmots (M. olympus and M. vancouverensis, respectively) are restricted to small isolated regions of the PNW. The endemic Vancouver Island marmot is currently classified as Critically Endangered and the Olympic marmot has recently experienced dramatic population declines. Previous phylogenetic studies of PNW marmot species have had limited power as they focused on resolving interspecific relationships, implicitly assumed an absence of gene flow among currently recognized species, included relatively few individuals, and relied heavily or entirely on mitochondrial DNA. We sequenced 2 mitochondrial and 4 nuclear markers from 167 hoary, 4 Vancouver Island, and 5 Olympic marmots in order to investigate phylogenetic relationships and historic gene flow among these species. We recovered 2 monophyletic (and predominantly allopatric) mitochondrial clades of hoary marmots that are not sister groups. Instead, Vancouver Island marmots formed a monophyletic mitochondrial sister clade to 1 of the hoary marmot clades. Nuclear loci did not recover the 2 mitochondrial clades of hoary marmots and suggest that Vancouver Island marmots may have experienced mitochondrial introgression from coastal mainland hoary marmots. Additionally, our nuclear results suggest possible gene flow between hoary and Olympic marmots despite different chromosomal formulas. Rather than resolving what has previously been considered a straightforward 3-taxon phylogenetic question, our findings suggest a complicated history of rapid divergence of the 3 species followed by intermittent and possibly ongoing gene flow between hoary marmots and both Olympic and Vancouver Island marmots. These results therefore have significant implications for the conservation of the latter 2 species, both of which are conservation concerns.

The common treeshrew, Tupaia glis, represents a species complex with a complicated taxonomic history. It is distributed mostly south of the Isthmus of Kra on the Malay Peninsula and surrounding islands. In our recent revision of a portion of this species complex, we did not fully assess the population from Java (T. “glis” hypochrysa) because of our limited sample. Herein, we revisit this taxon using multivariate analyses in comparisons with T. glis, T. chrysogaster of the Mentawai Islands, and T.ferruginea from Sumatra. Analyses of both the manus and skull of Javan T. “glis” hypochrysa show it to be most similar to T. chrysogaster and distinct from both T. glis and T. ferruginea. Yet, the Javan population and T. chrysogaster have different mammae counts, supporting recognition of T. hypochrysa as a distinct species. The change in taxonomic status of T. hypochrysa has conservation implications for both T. glis and this Javan endemic.

Alpine and arctic environments are thought to be more vulnerable to climate change than other lower-elevation and lower-latitude regions. Being both arctic and alpine distributed, the Alaska marmot (Marmota broweri) is uniquely suited to serve as a harbinger of the effects of climate change, yet it is the least-studied marmot species in North America. We investigated the phylogeography and genetic diversity of M. broweri throughout its known distribution in northern Alaska using the mitochondrial cytochrome b gene to better understand how post-Pleistocene changes and population fragmentation have structured genetic diversity. Our results show significant, although shallow, geographic structure among Alaska marmot populations. The diversity within and among populations is consistent with 2 phylogeographic hypotheses: Alaska marmots persisted in the eastern Brooks Range, Ray Mountains, and Kokrines Hills during the Pleistocene and have only recently expanded into the western Brooks Range; and the western Brooks Range served as a refugium as well and those populations have undergone a bottleneck resulting in reduced genetic variation in extant populations. Levels of mitochondrial deoxyribonucleic acid diversity are lower in M. broweri than in any other codistributed small mammal species and alpine mammal species with comparable data available. This is the 1st phylogeographic study of any marmot species and provides a baseline measure of the current structure and diversity within M. broweri.

The distribution and taxonomic status of the Alaska marmot (Marmota broweri) have been the subject of much debate and confusion since the taxon was 1st described as a subspecies of the hoary marmot (M. caligata). As a result of its early association with M. caligata and a lack of focused effort to determine its range, our current understanding of the distribution of M. broweri is vague at best and completely erroneous at worst. Through a review of all museum specimens and published accounts of this species, field surveys, and the identification of previously unidentified marmot specimens, we have determined that the current distribution of the Alaska marmot includes not only the Brooks Range, but also the Ray Mountains and Kokrines Hills of northern interior Alaska. We report the 1st confirmed records of this species outside of the Brooks Range and a commensurate range extension of 400 km southward. The Yukon River appears to form the current boundary between the parapatric distributions of M. broweri and M. caligata in Alaska, but additional fieldwork will be necessary to confirm that the 2 species are not allopatric.