Western Chipmunks Research Articles

Genomic resolution of cryptic species diversity in chipmunks.

Discovery of cryptic species is essential to understand the process of speciation and assessing the impacts of anthropogenic stressors. Here, we used genomic data to test for cryptic species diversity within an ecologically well-known radiation of North American rodents, western chipmunks (Tamias). We assembled a de novo reference genome for a single species (Tamias minimus) combined with new and published targeted sequence-capture data for 21,551 autosomal and 493 X-linked loci sampled from 121 individuals spanning 22 species. We identified at least two cryptic lineages corresponding with an isolated subspecies of least chipmunk (T. minimus grisescens) and with a restricted subspecies of the yellow-pine chipmunk (Tamias amoenus cratericus) known only from around the extensive Craters of the Moon lava flow. Additional population-level sequence data revealed that the so-called Crater chipmunk is a distinct species that is abundant throughout the coniferous forests of southern Idaho. This cryptic lineage does not appear to be most closely related to the ecologically and phenotypically similar yellow-pine chipmunk but does show evidence for recurrent hybridization with this and other species.

Hibernation Patterns in Grey Collared Chipmunks ( Neotamias cinereicollis )

Animals living in natural environments face daily and seasonal variation in environmental and ecological conditions. Winter is a major energetic challenge to temperate and arctic endotherms, as snow cover and low ambient temperature simultaneously reduce resource availability and increase resource requirements. Possible strategies that animals use to cope with these challenges include torpor and/or hibernation, when animals profoundly reduce body temperature and metabolic rate for several hours or weeks at a time. Chipmunks are small diurnal rodents considered to be facultative hibernators. Although western chipmunks (Neotamias spp) are represented by 23 species, most of our knowledge on chipmunk physiology and behavior comes from the Eastern chipmunk (Tamias striatus). Therefore, the aim of this study is to investigate the presence and patterns of hibernation in the grey collared chipmunk (Neotamias cinereicollis), a representative of the genus Neotamias. Also, we investigate the relationship between hibernation patterns and environmental conditions in a species assumed to be a facultative hibernator. We predict chipmunks display hibernation and that low temperatures and snow cover will be good predictors of hibernation length and onset. Grey collared chipmunks (n=7) were implanted intraperitoneally with body temperature loggers (iButtons: DS1922; Maxim) and housed in outdoor seminatural enclosures for a year where they experienced the natural weather regime but had access to food and water ad libitum. During this period, environmental variables were recorded (HOBO U30; Onset; Bourne-MA), including ambient temperature and snow cover. All chipmunks displayed hibernation starting late fall/early winter. Body temperature recordings indicated that chipmunks spend on average 81±29.5 days hibernating. During hibernation, torpor bouts averaged 3.17±2 days with the longest bout of torpor lasting for 10.1 days. During the hibernation season, average body temperature varied from 36.4±0.5C when euthermic to 5.6±3.6C during torpor bouts. The lowest body temperature recorded was -0.5C. Further analyses are being conducted to describe interrelationships among snow cover, ambient temperature and patterns of hibernation displayed by the chipmunks. Understanding hibernation patterns and their relationship with climate is important, as changes in climate and resource availability are expected to be major stressors for organisms, potentially leading to species decline.

No evidence for phylosymbiosis in western chipmunk species.

Phylosymbiosis refers to a congruent pattern between the similarity of microbiomes of different species and the branching pattern of the host phylogeny. Phylosymbiosis has been detected in a variety of vertebrate and invertebrate hosts, but has only been assessed in geographically isolated populations. We tested for phylosymbiosis in eight (sub)species of western chipmunks with overlapping ranges and ecological niches; we used a nuclear (Acrosin) and a mitochondrial (CYTB) phylogenetic marker because there are many instances of mitochondrial introgression in chipmunks. We predicted that similarity among microbiomes increases with: (1) increasing host mitochondrial relatedness, (2) increasing host nuclear genome relatedness and (3) decreasing geographic distance among hosts. We did not find statistical evidence supporting phylosymbiosis in western chipmunks. Furthermore, in contrast to studies of other mammalian microbiomes, similarity of chipmunk microbiomes is not predominantly determined by host species. Sampling site explained most variation in microbiome composition, indicating an important role of local environment in shaping microbiomes. Fecal microbiomes of chipmunks were dominated by Bacteroidetes (72.2%), followed by Firmicutes (24.5%), which is one of the highest abundances of Bacteroidetes detected in wild mammals. Future work will need to elucidate the effects of habitat, ecology and host genomics on chipmunk microbiomes.

Evolutionary processes and its environmental correlates in the cranial morphology of western chipmunks (Tamias).

The importance of the environment in shaping phenotypic evolution lies at the core of evolutionary biology. Chipmunks of the genus Tamias (subgenus Neotamias) are part of a very recent radiation, occupying a wide range of environments with marked niche partitioning among species. One open question is if and how those differences in environments affected phenotypic evolution in this lineage. Herein we examine the relative importance of genetic drift versus natural selection in the origin of cranial diversity exhibited by clade members. We also explore the degree to which variation in potential selective agents (environmental variables) are correlated with the patterns of morphological variation presented. We found that genetic drift cannot explain morphological diversification in the group, thus supporting the potential role of natural selection as the predominant evolutionary force during Neotamias cranial diversification, although the strength of selection varied greatly among species. This morphological diversification, in turn, was correlated with environmental conditions, suggesting a possible causal relationship. These results underscore that extant Neotamias represent a radiation in which aspects of the environment might have acted as the selective force driving species' divergence.

Temporal and spatial mosaics: deep host association and shallow geographic drivers shape genetic structure in a widespread pinworm, Rauschtineria eutamii.

Climate and host demographic cycling often shape both parasite genetic diversity and host distributions, processes that transcend a history of strict host-parasite association. We explored host associations and histories based on an evaluation of mitochondrial and nuclear sequences to reveal the underlying history and genetic structure of a pinworm, Rauschtineria eutamii, infecting 10 species of western North American chipmunks (Rodentia:Tamias, subgenus Neotamias). Rauschtineria eutamii contains divergent lineages influenced by the diversity of hosts and variation across the complex topography of western North America. We recovered six reciprocally monophyletic R. eutamii mitochondrial clades, largely supported by nuclear gene trees, exhibiting divergence levels comparable to intraspecific variation reported for other nematodes. Phylogenetic relationships among pinworm clades suggest that R. eutamii colonized an ancestral lineage of western chipmunks and lineages persisted during historical isolation in diverging Neotamias species or species groups. Pinworm diversification, however, is incongruent and asynchronous relative to host diversification. Secondarily, patterns of shallow divergence were shaped by geography through events of episodic colonization reflecting an interaction of taxon pulses and ecological fitting among assemblages in recurrent sympatry. Pinworms occasionally infect geographically proximal host species; however, host switching may be unstable or ephemeral, as there is no signal of host switching in the deeper history of R. eutamii.

Phylogeny Estimation of the Radiation of Western North American Chipmunks (Tamias) in the Face of Introgression Using Reproductive Protein Genes

The causes and consequences of rapid radiations are major unresolved issues in evolutionary biology. This is in part because phylogeny estimation is confounded by processes such as stochastic lineage sorting and hybridization. Because these processes are expected to be heterogeneous across the genome, comparison among marker classes may provide a means of disentangling these elements. Here we use introns from nuclear-encoded reproductive protein genes expected to be resistant to introgression to estimate the phylogeny of the western chipmunks (Tamias: subgenus: Neotamias), a rapid radiation that has experienced introgressive hybridization of mitochondrial DNA (mtDNA). We analyze the nuclear loci using coalescent-based species-tree estimation methods and concatenation to estimate a species tree and we use parametric bootstraps and coalescent simulations to differentiate between phylogenetic error, coalescent stochasticity and introgressive hybridization. Results indicate that the mtDNA gene tree reflects several introgression events that have occurred between taxa of varying levels of divergence and at different time points in the tree. T. panamintinus and T. speciosus appear to be fixed for ancient mitochondrial introgressions from T. minimus. A southern Rocky Mountains clade appears well sorted (i.e., species are largely monophyletic) at multiple nuclear loci, while five of six taxa are nonmonophyletic based on cytochrome b. Our simulations reject phylogenetic error and coalescent stochasticity as causes. The results represent an advance in our understanding of the processes at work during the radiation of Tamias and suggest that sampling reproductive-protein genes may be a viable strategy for phylogeny estimation of rapid radiations in which reproductive isolation is incomplete. However, a genome-scale survey that can statistically compare heterogeneity of genealogical process at many more loci will be necessary to test this conclusion.

Molecular Systematics of Chipmunks (Neotamias) Inferred by Mitochondrial Control Region Sequences

Western chipmunks (Neotamias) exhibit a complex geographical distribution and can vary by minute morphological differences. This has lead to confusion around the taxonomy and evolutionary history of this group. The main focus of this molecular study was to infer taxonomic relationships within Neotamias, especially at the tips of the tree. Sequences of the complete control region for 16 species of chipmunks (Tamias, Neotamias) were analyzed independently and in combination with previously published sequences of two mitochondrial genes, cytochrome b and cytochrome oxidase II. The control region data set corroborated the findings of Piaggio and Spicer (2001) in finding five discrete clades, while also providing stronger bootstrap support for most terminal branches. Analysis of individual mitochondrial genes revealed that not all genes have the same phylogenetic signal and when analyzed in combination, this incongruence amongst genes is resolved.

Geographic Variation of the Western Chipmunks Tamias Senex and T. Siskiyou, with Two New Subspecies from California

Geographic Variation of the Western Chipmunks Tamias Senex and T. Siskiyou, with Two New Subspecies from California

GEOGRAPHIC VARIATION OF THE WESTERN CHIPMUNKSTAMIAS SENEXANDT. SISKIYOU,WITH TWO NEW SUBSPECIES FROM CALIFORNIA

Three species of western chipmunks, Tamias senex, T. siskiyou, and T. ochrogenys, were removed from T. townsendii because discrete character variation, especially of genitalic morphology, suggested lack of intergradation and species-level distinction. Two of these species, T. senex and T. siskiyou, show substantial geographic variation in cranial morphology and pelage characteristics across their ranges, from humid coastal forests to the relatively arid Sierra Nevada and Cascade ranges in northern California. In both species, specimens from inland localities are paler and smaller than those collected near the Pacific coast. This also is true for another species in Oregon and Washington, where coastal T. t. townsendii is replaced by inland T. t. cooperi. Interspecific convergence in pelage and external variation is so strong that inland T. senex and T. siskiyou resemble each other more strongly than either resembles conspecifics from coastal forests, and vice versa. In spite of this convergence, genital bones confirm the specific identity of inland and coastal specimens. Because both T. senex and T. siskiyou were originally described from inland localities, the novel patterns of color and size described here provide the basis for naming the coastal forms as new subspecies.

Context-specific alarm calls of the eastern chipmunk, Tamias striatus

The structure and context of alarm calls produced by chipmunks (Tamias striatus) at a field site in southern Quebec were recorded during opportunistic field observations and experimentally simulated hawk attacks. Chipmunks produced three call types in the presence of predators. Chipping consisted of a series of high frequency notes with a rapid downward frequency slope (9.6 to 2.8 kHz) and was given in the presence of mammalian predators by chipmunks perched on a raised vantage point. Chucking consisted of a series of lower frequency notes also sloping downwards (2.5 to 0.4 kHz), given in the presence of avian predators by perched animals. The trill was a lower amplitude, multi-note call usually given only once by animals before reaching a refuge while fleeing from either type of predator. The average trill contained 6–11 downward sloping notes (7.3 to 0.8 kHz). The alarm call types of eastern chipmunks appear to be similar to those reported for western chipmunks. However, they differ in the clear separation of the calls for aerial and terrestrial predators. Chipmunks differ from most other terrestrial sciurids in giving repeated calls for aerial as well as terrestrial predators and in using a call just before reaching a secure refuge.

Adaptive cardiovascular modifications in the western chipmunks genusEutamias

Metabolic and cardiovascular parameters were studied in four western chipmunks, genusEutamias, to elucidate the mechanisms underlying the maintenance of normal aerobic metabolism while the heart rate were profoundly depressed (Jones and Wang, 1976). It was postulated that cardiovascular adaptations involving either an increase of stroke volume and/or an increase of arterial-venous oxygen difference (A-V O2) must have evolved to account for such alterations (Jones and Wang, 1976). Simultaneous measurements of O2 consumption, heart rate and A-V O2 were made in anesthetized animals at thermal neutral temperature of 25°C. The mean cardiac output ranged between 16.2–23.5 ml/min, and the calculated stroke volume was between 0.032–0.057 ml/beat, not atypical for similar sized mammals (Table 1). Measurements of heart weight as an indirect indicator for stroke volume also indicated normal stroke volume in the chipmunks (Table 2). The mean A-V O2, on the other hand, was between 5.6–10.4 vol % (Table 1), comparatively greater than the 4–6 vol % typical of resting mammals. The measured hematocrit, hemoglobin concentration, red blood cell counts, and blood volume, were within the range of values for similar sized mammals (Table 3), suggesting normal O2 capacity as well as O2 content carried in blood. Taken together, it was concluded that the major cardiovascular modification in the chipmunks while accomplishing normal aerobic metabolism under profoundly depressed heart rates is by the increased ability to extract O2 across the capillary beds. Possible mechanisms relating to this adaptation are discussed.

Metabolic and cardiovascular adaptations in the western chipmunks, genusEutamias

The metabolic and cardiac responses to temperature were studied in two species (four subspecies) of western chipmunks (genusEutamias), inhabiting boreal and alpine environments. A specially designed (Fig. 1) implantable biopential radiotransmitter was used to measure heart rate in unrestrained animals. The estimated basal metabolic rates (EBMR) were 1.78 (E. minimus borealis), 1.64 (E. m. oreocetes), 1.50 (E. m. operarius), and 1.69 ml O2 g−1 h−1 (E. amoenus luteiventris), or 839, 752, 698, and 628 ml O2 kg−0.75 h−1, respectively, for the four subspecies (Table 1). The two alpine species (E.m.or. andE.m.op.) had significantly lower EBMR than both of their boreal counterparts. The EBMR from all animals are 120–135% of the predicted values based on body weights of the animals. The thermal neutral zone for the four subspecies ranged from 23.5 to 32°C and the minimum thermal conductances were 0.113, 0.111, 0.112 and 0.112 ml O2 g−1 h−1 °C−1, respectively, or 54.4, 54.0, 50.4 and 52.1 ml O2 kg−0.75 h−1 °C−1, respectively (Fig. 2). No interspecific diffence in conductance was observed. These values are 72 to 85% of their weight specific values. The body temperature ranged between 35.0 and 39.5°C and was usually maintained between 36 and 38°C in all subspecies between ambient temperatures of 3 and 32°C. The estimated basal heart rates were 273, 296, 273 and 264 beats/min, respectively, for the four subspecies, 49–55% of their predicted weight specific values. The resultant oxygen pulses (metabolic rate/heart rate) were 5.49, 4.50, 4.48 and 5.56×10−3 ml O2/beat, respectively, which are 2 to 2.4 times their weight specific values (Table 2).

Influence of athletic training on hemoglobin-oxygen affinity.

ARTICLESInfluence of athletic training on hemoglobin-oxygen affinityPW Rand, JM Norton, N Barker, and M LovellPW Rand, JM Norton, N Barker, and M LovellPublished Online:01 Jun 1973https://doi.org/10.1152/ajplegacy.1973.224.6.1334MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByEffects of short hypoxic pre-exposure on physiological responses to subsequent hypoxic exerciseThe Journal of Physical Fitness and Sports Medicine, Vol. 4, No. 2Exercice, entraînement et âge érythrocytaireScience & Sports, Vol. 5, No. 4Consequences of 6 weeks of strength training on red cell O2 transport and iron statusEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 60, No. 3Effects of training on erythrocyte 2,3-diphosphoglycerate in normal menEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 57, No. 4Gas Exchange in Exercise1 January 2011Intermittent claudication, exercise, and blood rheology.Circulation, Vol. 76, No. 5Beneficial effects of exercising at moderate altitude on red cell oxygen transport and on exercise performancePfl�gers Archiv European Journal of Physiology, Vol. 406, No. 6The Effect of Training and Physical Exercise on the Energetic Metabolism of Equine Erythrocytes13 May 2010 | Zentralblatt für Veterinärmedizin Reihe A, Vol. 32, No. 1-10Effect of long-term training and acute physical exercise on red cell 2,3-diphosphoglycerateEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 42, No. 3Oxygen dissociation curves in trained and untrained subjectsEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 42, No. 1Physiological effects of lowered blood oxygen affinity in dogsRespiration Physiology, Vol. 33, No. 3Training and exercise change respiratory properties of blood in race horsesRespiration Physiology, Vol. 29, No. 3LiteraturAdaptive cardiovascular modifications in the western chipmunks genusEutamiasJournal of Comparative Physiology ? B, Vol. 112, No. 3The oxyhemoglobin dissociation curve in health and diseaseThe American Journal of Medicine, Vol. 57, No. 3Influence of altitude training on muscle metabolism and performance in man.British Journal of Sports Medicine, Vol. 8, No. 1 More from this issue > Volume 224Issue 6June 1973Pages 1334-1337 Copyright & PermissionsCopyright © 1973 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1973.224.6.1334PubMed4712147History Published online 1 June 1973 Published in print 1 June 1973 Metrics

Measurements of Convective and Radiative Heat Transfer in Small Mammals

The coefficient of convection and the effective surface area for the emission and absorption of thermal radiation are two physical characteristics of an organism that must be quantified before the energy budget of that organism can be calculated. These two parameters were measured by using internally heated, pelt-covered metal casts of four species of western chipmunks ( Eutamias alpinus, E. speciosus, E. amoenus , and E. minimus ). The casts were suspended in a vacuum and the effective radiating surface area (Aee) was calculated from the wattage necessary to maintain a constant cast radiating surface temperature ( Tr ), Tr , and chamber surface temperature. The casts were placed in a wind tunnel and the coefficients of convection at different wind speeds were calculated from Tr , wattage necessary to maintain that Tr, air temperature, tunnel wall temperature, and total cast surface area.

Altitudinal Zonation of Chipmunks (Eutamias): Adaptations to Aridity and High Temperature

Fecal, urinary and evaporative water losses were mea- sured at 15 C, 50-75% relative humidity for four species of western chipmunks (Eutamias) which are contiguously allopatric and alti- tudinally zoned on the eastern slope of the Sierra Nevada, California. Evaporative loss and hyperthermia were also studied for acute exposures to 25, 35 and 40 C. Differences in total water budgets, calculated for 35 C and 11% relative humidity are not important in determining the lines of contact, starting from the alpine and descending toward the desert, between E. alpinus and E. speciosus or between E. speciosus and E. amoenus. But they may play a role in preventing E. am,oenus from colonizing the desert sagebrush habitat occupied by E. minimus. E. minimus can be active in the open areas of the hot, arid sagebrush desert by minimizing evaporative water loss and tolerating increased body heat content; this species frequently retreats to, its burrows to un- load excess body heat. When large patches of shade are available from pifion pines the aggressively dominant E. amoenus can occupy the sage- brush habitat. Hence, in the field area of this study the line of contact between E. amoenus and E. minimus coincides with the lower limits of the pifion pine.

Seasonal variation of myoglobin in the northern red-backed vole.

ARTICLESSeasonal variation of myoglobin in the northern red-backed voleP Morrison, M Rosenmann, and JA SealanderP Morrison, M Rosenmann, and JA SealanderPublished Online:01 Dec 1966https://doi.org/10.1152/ajplegacy.1966.211.6.1305MoreSectionsPDF (776 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByPinniped Ontogeny as a Window into the Comparative Physiology and Genomics of Hypoxia Tolerance19 June 2020 | Integrative and Comparative Biology, Vol. 60, No. 6Postnatal development of diving physiology: implications of anthropogenic disturbance for immature marine mammals11 September 2020 | Journal of Experimental Biology, Vol. 223, No. 17Rapid maturation of the muscle biochemistry that supports diving in Pacific walruses ( Odobenus rosmarus divergens )Journal of Experimental Biology, Vol. 218, No. 20Living in the fast lane: rapid development of the locomotor muscle in immature harbor porpoises (Phocoena phocoena)23 August 2014 | Journal of Comparative Physiology B, Vol. 184, No. 8Age-related differences in skeletal muscle lipid profiles of Weddell seals: clues to developmental changesJournal of Experimental Biology, Vol. 213, No. 10Total body oxygen stores and physiological diving capacity of California sea lions as a function of sex and ageJournal of Experimental Biology, Vol. 210, No. 2Development of the Blood and Muscle Oxygen Stores in Gray Seals ( Halichoerus grypus ): Implications for Juvenile Diving Capacity and the Necessity of a Terrestrial Postweaning FastPhysiological and Biochemical Zoology, Vol. 78, No. 4Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?Journal of Experimental Biology, Vol. 206, No. 7Myoglobin content in skeletal muscles of hibernating ground squirrels rises in autumn and winterComparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, Vol. 124, No. 1Thermal freedom of Graomys griseoflavus in a seasonal environmentComparative Biochemistry and Physiology Part A: Physiology, Vol. 87, No. 2Myoglobin levels and mATPase activity in pectoral muscles of spruce and ruffed grouse (Aves: Tetraoninae)Comparative Biochemistry and Physiology Part A: Physiology, Vol. 81, No. 1Muscle myoglobin and flying habits in birdsComparative Biochemistry and Physiology Part A: Physiology, Vol. 74, No. 2Diurnal variation in the distribution of lipid in the pectoralis muscle of the House sparrow (Passer domesticus)20 August 2009 | Journal of Zoology, Vol. 191, No. 4Effects of chronic exposure to cold or hypoxia on ventricular weights and ventricular myoglobin concentrations in guinea pigs during growthPflügers Archiv, Vol. 385, No. 2The effect of flying and not flying on myoglobin content of heart muscle of the pigeon Columbia livia domesticaComparative Biochemistry and Physiology Part A: Physiology, Vol. 59, No. 4Adaptive cardiovascular modifications in the western chipmunks genusEutamiasJournal of Comparative Physiology ? B, Vol. 112, No. 3Myoglobin in Primary Muscular Disease: I. Duchenne Muscular Dystrophy: and: II. Muscular Dystrophy of Distal TypeJournal of Medical Genetics, Vol. 10, No. 4Size and Seasonal Change in DimensionsJahresrhythmus der Glucoseutilisation des eviscerierten Kaninchens sowie des isolierten perfundierten RattenherzensPfl�gers Archiv European Journal of Physiology, Vol. 319, No. 1The Role of Skeletal and Cardiac Muscle in the Regulation of Protein MetabolismResponse of isozymes to torpor in the rat, Eptesicus fuscusComparative Biochemistry and Physiology, Vol. 27, No. 1Reproductive status and adrenal size in the northern red-backed vole in relation to seasonInternational Journal of Biometeorology, Vol. 11, No. 2 More from this issue > Volume 211Issue 6December 1966Pages 1305-1308 Copyright & PermissionsCopyright © 1966 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1966.211.6.1305PubMed5956540History Published online 1 December 1966 Published in print 1 December 1966 Metrics

Contributions of Chromosomal Analysis to the Systematics of North American Chipmunks

Chromosomes from the bone marrow of 32 chipmunks belonging to the genera Eutamias and Tamias were analyzed using a colcemide, hypotonic citrate, acetic orcein squash technique. The modal diploid chromosome number was 38 in Eutamias minimus caryi, E. m. consobrinus, E. m. neglectus, E. q. quadrivittatus, E. speciosus frater, E. a. amoenus, E. t. townsendii, E. t. cooperi, E. t. senex, E. d. dorsalis and Tamias striatus griseus. Three distinctive chromosomal patterns were observed among these species. The first pattern, found only among specimens of Eutamias minimus was designated Eutamias Karyotype A. Chromosomal patterns of E. quadrivittatus, E. speciosus, E. amoenus, E. townsendii and E. dorsalis were similar and were collectively designated Eutamias Karyotype B. A third chromosomal pattern, found in Tamias striatus, was named the Tamias Karyotype. The sex chromosomes of all species were of the X-Y type. Correlation of chromosomal characters with present concepts of chipmunk systematics suggests that chromosomal data is most meaningful at the generic and infrageneric levels. A close chromosomal relationship was found between Eutamias and Tamias. The observation of two distinct karyotypes within Eutamias suggests there may be two species groups in this genus and zoogeographic data support this new concept. Evolution of chipmunks is discussed and it is postulated that the Nearctic Region was populated by two or possibly three separate eastward invasions of chipmunks from the Palearctic Region. The systematics of the presently recognized chipmunk genera, Eutamias and Tamias, have undergone a number of revisions, each based on a variety of characters. The first extensive revision of the chipmunk genera was presented by Howell (1929) and was based on examination of cranial and external characters from a large series of specimens representing 16 species of Eutamias and one species of Tamias. Howell reviewed the earlier works of Allen (1877, 1890) and others, and relegated all chipmunks to two genera: Tamias for the eastern North American chipmunks; and Eutamias subgenus Eutamias for Asiatic chipmunks, and subgenus Neotamias for the chipmunks of western North America. Ellerman (1940), proposed a different classification of chipmunks in which Eutamias, Neotamias and Tamias were all given subgeneric rank within the single genus Tamias. Cranial morphology, dentition, and external features formed the basis for this decision. In an extensive phylogenetic study of Sciuridae, Bryant (1945) re-evaluated the problem using not only cranial and external characters but other skeletal and dental characters, myology and paleontology as well. He agreed with the classification proposed by Ellerman (1940) and concluded that the differences between eastern and western chipmunks were not of sufficient phylogenetic importance to warrant retention of the two groups as separate genera. More recently, White

Brood Nests and Young of Two Western Chipmunks in the Olympic Mountains of Washington

Journal Article Brood Nests and Young of Two Western Chipmunks in the Olympic Mountains of Washington Get access William T. Shaw William T. Shaw 1002 Cambridge Ave., Fresno 4, California Search for other works by this author on: Oxford Academic Google Scholar Journal of Mammalogy, Volume 25, Issue 3, 8 September 1944, Pages 274–284, https://doi.org/10.2307/1374701 Published: 08 September 1944

A Contribution to the Biology of Ornithodoros hermsi Wheeler, Herms and Meyer

This species of tick is a parasite of small mammals, particularly rodents, with the most favored host the western chipmunks, Eutamtias spp. The majority of ticks in California were taken from the nesting material of these animals found in the attics and between the walls of some of the cabins and cottages in several of the mountain resort areas (Herms and Wheeler, 1935). Other specimens have been found in nesting material of chipmunks situated in old hollow logs while several were removed from the sleeping bag of a deer hunter. In Colorado many ticks of this species were collected from chipmunk nesting material in a decaying Douglas fir stump (Davis, 1941). No ticks have been discovered in the nests of the chickaree squirrel, Sciurus douglasii, although this species of rodent is another proven reservoir of the spirochetes of relapsing fever. That these squirrels locate their nests high in trees making search extremely difficult in all probability accounts for the fact that no ticks have been taken from the nests of these animals.