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Abstract Understanding habitat associations is vital for conservation of at‐risk marsh‐endemic wildlife species, particularly those under threat from sea level rise. We modeled environmental and habitat associations of the marsh‐endemic, Federally endangered salt marsh harvest mouse (Reithrodontomys raviventris, RERA) and co‐occurrence with eight associated small mammal species from annual trap data, 1998–2014, in six estuarine marshes in North San Francisco Bay, California. Covariates included microhabitat metrics of elevation and vegetation species and cover; and landscape metrics of latitude–longitude, distance to anthropogenic features, and habitat patch size. The dominant cover was pickleweed (Salicornia pacifica) with 86% mean cover and 37 cm mean height, and bare ground with about 10% mean cover. We tested 38 variants of Bayesian network (BN) models to determine covariates that best account for presence of RERA and of all nine small mammal species. Best models had lowest complexity and highest classification accuracy. Among RERA presence models, three best BN models used covariates of latitude–longitude, distance to paved roads, and habitat patch size, with 0% error of false presence, 20% error of false nonpresence, and 20% overall error. The all‐species presence models suggested that within the pickleweed marsh environment, RERA are mostly habitat generalists. Accounting for presence of other species did not improve prediction of RERA. Habitat attributes compared between RERA and the next most frequently captured species, California vole (Microtus californicus), suggested substantial habitat overlap, with RERA habitat being somewhat higher in marsh elevation, greater in percent cover of the dominant plant species, closer to urban areas, further from agricultural areas, and, perhaps most significant, larger in continuous size of marsh patch. Findings will inform conservation management of the marsh environment for RERA by identifying best microhabitat elements, landscape attributes, and adverse interspecific interactions.

Understanding habitat associations is vital for conservation of at‐risk marsh‐endemic wildlife species, particularly those under threat from sea level rise. We modeled environmental and habitat associations of the marsh‐endemic, Federally endangered salt marsh harvest mouse (Reithrodontomys raviventris, RERA) and co‐occurrence with eight associated small mammal species from annual trap data, 1998–2014, in six estuarine marshes in North San Francisco Bay, California. Covariates included microhabitat metrics of elevation and vegetation species and cover; and landscape metrics of latitude–longitude, distance to anthropogenic features, and habitat patch size. The dominant cover was pickleweed (Salicornia pacifica) with 86% mean cover and 37 cm mean height, and bare ground with about 10% mean cover. We tested 38 variants of Bayesian network (BN) models to determine covariates that best account for presence of RERA and of all nine small mammal species. Best models had lowest complexity and highest classification accuracy. Among RERA presence models, three best BN models used covariates of latitude–longitude, distance to paved roads, and habitat patch size, with 0% error of false presence, 20% error of false nonpresence, and 20% overall error. The all‐species presence models suggested that within the pickleweed marsh environment, RERA are mostly habitat generalists. Accounting for presence of other species did not improve prediction of RERA. Habitat attributes compared between RERA and the next most frequently captured species, California vole (Microtus californicus), suggested substantial habitat overlap, with RERA habitat being somewhat higher in marsh elevation, greater in percent cover of the dominant plant species, closer to urban areas, further from agricultural areas, and, perhaps most significant, larger in continuous size of marsh patch. Findings will inform conservation management of the marsh environment for RERA by identifying best microhabitat elements, landscape attributes, and adverse interspecific interactions. [ABSTRACT FROM AUTHOR]

Voles (Cricetidae) cause extensive damage to a variety of crops throughout much of the Northern Hemisphere. The removal of vegetation from crop fields at the end of the growing season, combined with a subsequent burrow fumigant application of aluminum phosphide, has the potential to substantially curtail vole activity but has not been thoroughly examined. We set up a study to test the impact of these management tools in perennial globe artichoke (Cynara cardunculus var. scolymus) fields in Monterey County, CA, during 2010 and 2011, to determine their potential utility as part of an integrated pest management (IPM) program for managing California voles (Microtus californicus). We used both chewing indices and mortality estimates derived via radiotelemetry to assess the efficacy of aboveground vegetation removal and aluminum phosphide applications on vole abundance. We determined the impact of plowing artichoke fields on vole activity as well. Both removal of vegetation and applications of aluminum phosphide substantially reduced vole presence within treated fields. Plowing also reduced vole abundance to the point of little residual activity following treatment. These management practices appear to be effective at eliminating voles from crop fields. Combining these tools with management practices designed to slow down reinvasion by neighboring vole populations (e.g., barriers, repellents, traps) has the potential to substantially reduce farmer reliance on rodenticides for vole management, although rodenticides will still be needed to curtail populations that reestablish within crop fields. Such an IPM approach should substantially benefit both farmers and agro-ecosystems. [ABSTRACT FROM AUTHOR]

We clarify misleading published information on the distribution of the endangered California vole (Microtus californicus) in Baja California, Mexico. We photo-document recent records for 2 of the 4 subspecies reported from Mexico and provide a map that includes several locations not previously published. [ABSTRACT FROM AUTHOR]

Abstract: To examine the processes that maintain genetic diversity among closely related taxa, we investigated the dynamics of introgression across a contact zone between two lineages of California voles (Microtus californicus). We tested the prediction that introgression of nuclear loci would be greater than that for mitochondrial loci, assuming ongoing gene flow across the contact zone. We also predicted that genomic markers would show a mosaic pattern of differentiation across this zone, consistent with genomes that are semi‐permeable. Using mitochondrial cytochrome b sequences and genome‐wide loci developed via ddRAD‐seq, we analyzed genetic variation for 10 vole populations distributed along the central California coast; this transect included populations from within the distributions of both parental lineages as well as the putative contact zone. Our analyses revealed that (1) the two lineages examined are relatively young, having diverged ca. 8.5–54 kya, (2) voles from the contact zone in Santa Barbara County did not include F1 or early generation backcrossed individuals, and (3) there appeared to be little to no recurrent gene flow across the contact zone. Introgression patterns for mitochondrial and nuclear markers were not concordant; only mitochondrial markers revealed evidence of introgression, putatively due to historical hybridization. These differences in genetic signatures are intriguing given that the contact zone occurs in a region of continuous vole habitat, with no evidence of past or present physical barriers. Future studies that examine specific isolating mechanisms, such as microhabitat use and mate choice, will facilitate our understanding of how genetic boundaries are maintained in this system. [ABSTRACT FROM AUTHOR]

Vole (Cricetidae) girdling of tree trunks is a common form of damage experienced by tree and vine growers throughout much of the Northern Hemisphere. Management programs that effectively incorporate chemical repellents and vegetation management would be of substantial assistance to growers that experience such damage. Anthraquinone has proven effective as a repellent against voles in lab trials, yet controlled field tests of combined anthraquinone and vegetation management programs are lacking. Therefore, we established a mesocosm-based study in central California, USA, to test the efficacy of anthraquinone and vegetation management for reducing girdling damage caused by California voles Microtus californicus to Clementine citrus trees Citrus clementine under semi-field conditions. We observed a 90-100% reduction in girdling damage for trees following a single application of anthraquinone during two trials in summer and spring, respectively. Removal of vegetation around the base of trees further reduced damage during the summer sampling period, with no girdling observed on anthraquinone-treated trees that were surrounded by bare soil. We did not observe this same relationship during spring, and we observed no relationship between vegetation management in the absence of anthraquinone treatments in either seasonal trial, suggesting that vegetation management had a lesser impact on vole girdling than anthraquinone applications. We observed no decrease in efficacy of anthraquinone across the duration of both sampling periods (5-6 weeks), indicating substantial longevity for anthraquinone. Anthraquinone appears to have substantial utility for minimizing vole girdling damage. Field testing is warranted for additional mammalian species to determine potential uses for other taxa. [ABSTRACT FROM AUTHOR]

Understanding population genetic structure and levels of genetic variation is critical for the conservation and management of imperiled populations, especially when reintroductions are planned. We used restriction-site associated DNA (RAD) sequencing to study the genetic diversity and evolutionary relationships of the endangered Amargosa vole and other closely related desert-dwelling California voles. Specifically, we sought to determine how Amargosa voles are related to other California voles, how genetic variation is partitioned among subpopulations in wild Amargosa voles, and how much genetic variation is captured within a captive insurance colony of Amargosa voles. Our multilocus nuclear dataset provides strong evidence that Amargosa voles are part of a northern clade of California voles. Amargosa voles have highly reduced genetic variation relative to other California voles, but do exhibit some sub-structure among sampled marshes. Captive Amargosa voles capture approximately half of the total genetic variation present in the wild Amargosa vole populations. We discuss the management implications of our findings in light of reintroductions planned for Amargosa voles. Our study highlights the utility of reduced representation genomic approaches, like RADseq, to resolve relationships among small populations that are difficult to study with traditional markers due to low genetic variation and few individuals left in the wild. [ABSTRACT FROM AUTHOR]

We examined geographic trends in 4 morphological data sets (both craniodental and colorimetric measurements and scores of cranial foramina and qualitative craniodental variables) within and among 5 subspecies of the California vole, Microtus californicus, that occur within or adjacent to the Mojave Desert in eastern California. These analyses are corollary to those previously published on the same samples using both mitochondrial and nuclear gene sequences and microsatellite loci. The morphological and molecular data sets are generally concordant in supporting the existing infraspecific taxonomy, although important conflicts are evident. With the combination of data sets, we are able to assign previously unknown samples to these infraspecific taxa. We define and provide an emended diagnosis of each subspecies using the criteria established by Willi Hennig in his 1966 assessment of the qualities and characteristics of infraspecific taxa, which he understood to be fundamentally different than the hierarchical phylogenetic system he established as the conceptual framework for taxa at the species level and above. Hennig's views are contrary to how the subspecies concept has been applied in much of recent mammalian taxonomy. [ABSTRACT FROM AUTHOR]

We provide a record and field observations of California vole ( Microtus californicus) based on a specimen collected on 5 June 2013 in riparian habitat from Arroyo San Rafael, northwestern Sierra San Pedro Mártir, Baja California, México. The last known record of this species in México was in 1974. This species was suspected to be extirpated from México; however, our recent record confirms its present occurrence in this country. [ABSTRACT FROM AUTHOR]

The California vole, Microtus californicus, restricted to habitat patches where water is available nearly year-round, is a remnant of the mesic history of the southern Great Basin and Mojave deserts of eastern California. The history of voles in this region is a model for species-edge population dynamics through periods of climatic change. We sampled voles from the eastern deserts of California and examined variation in the mitochondrial cytb gene, three nuclear intron regions, and across 12 nuclear microsatellite markers. Samples are allocated to two mitochondrial clades: one associated with southern California and the other with central and northern California. The limited mt DNA structure largely recovers the geographical distribution, replicated by both nuclear introns and microsatellites. The most remote population, Microtus californicus scirpensis at Tecopa near Death Valley, was the most distinct. This population shares microsatellite alleles with both mt DNA clades, and both its northern clade nuclear introns and southern clade mt DNA sequences support a hybrid origin for this endangered population. The overall patterns support two major invasions into the desert through an ancient system of riparian corridors along streams and lake margins during the latter part of the Pleistocene followed by local in situ divergence subsequent to late Pleistocene and Holocene drying events. Changes in current water resource use could easily remove California voles from parts of the desert landscape. [ABSTRACT FROM AUTHOR]

Combination baits containing cholecalciferol plus an anticoagulant are effective against commensal rodents resistant to anticoagulants, and they likely pose less risk than anticoagulant-only rodenticides due to lower concentrations of active ingredients and shorter time to death. However, these combination baits have not been tested for agricultural rodent pests. Therefore, we established a study to test the efficacy of cholecalciferol plus diphacinone artichoke bract and pellet baits to determine their ability to manage California voles Microtus californicus in artichokes, where resistance to anticoagulants is known to occur. Field tests using radiocollared voles indicated that bract baits were highly efficacious (85 %), although pellet baits were less effective (60 %). Low observed efficacy of pellet baits may have resulted from poor weather following application during the second sampling period; further testing may yield more positive results. We observed a bimodal distribution in timing of death, with one group of voles dying between 4.3 and 5.8 days post-consumption; the other group died between 9.0 and 14.5 days post-consumption. Deaths in the first group were attributed to cholecalciferol, while deaths in the second group were likely due to chronic anticoagulant exposure. Almost double the proportion of voles that died from bract consumption did so during the early period when compared to their pellet plot counterparts. This suggests that voles were consuming greater quantities of bract baits over a shorter period of time when compared to the pellet bait. Collectively, these findings indicate that baiting with cholecalciferol plus diphacinone coated bracts is an effective method for controlling vole populations in artichokes. [ABSTRACT FROM AUTHOR]

Rodents have been noteworthy pests in agricultural areas for decades. Because rodents impact diverse ecosystems, anticoagulant rodenticides have been heavily used throughout the world to control rodent populations. This continued use has led to the development of resistance to anticoagulant rodenticides in some populations of targeted rodents. Although many studies have investigated the genetic and molecular basis of anticoagulant resistance, few have focused on potential changes in metabolic function of resistant animals. In this study, vole ( Microtus californicus , Peale) liver microsome preparations were made from unexposed animals living in areas that had never used anticoagulant rodenticides for either crop protection or for the control of commensal rodents and exposed voles living in artichoke fields that have used anticoagulant rodenticides since the mid-1990s. Using these microsome preparations, the metabolism of diphacinone and chlorophacinone was tested. Microsomes from both male and female voles from exposed areas metabolized significantly more anticoagulant than unexposed animals. Also, both exposed and unexposed animals metabolized more diphacinone than chlorophacinone. These findings suggest that alterations in metabolic function may play a role in anticoagulant resistance. [ABSTRACT FROM AUTHOR]

Arvicoline rodents serve as model organisms for investigating the intricacies of ecological/evolutionary feedbacks that characterize multiannual fluctuations in abundance. A population of California voles (Microtus californicus) in central California was followed for 3.5 years using 4 small grids located 50 m apart. Blood samples were scored for 4 polymorphic allozyme loci by starch gel electrophoresis. These were carefully chosen for their potential to reveal details of genetic structuring among demes. A low density of voles developed into a peak followed by a rapid decline to low density. Heterozygosity averaged 20.2% (n = 709) with loci-specific shifts associated with density, season, and cyclic phase. Statistically significant heterogeneity in genotypic and allelic frequencies among the grids was found for 3 of the loci. Pairwise comparisons among the grids for each locus separately (n = 24) yielded 11 significantly disparate pairs for genotypic frequencies and 10 for alleles. Significant correlations with cyclic phase were found at 1 locus (leucine aminopeptidase). Spatial differentiation among grid pairs (FST) ranged up to a 12-fold difference. FST values stratified by cyclic phase showed the highest levels in the pre-high phase and the lowest in the postpeak. A "founder/lush" model with sequential phases of semi-isolated low-density demes followed by panmixia at high densities, and then a density crash is supported. This pattern is postulated to facilitate adaptive evolution. [ABSTRACT FROM AUTHOR]

The Owens Valley vole ( Microtus californicus vallicola) exists in populations fragmented by natural aridity, land cultivation, highways and canals, and local urbanization. We used genetic analysis of six microsatellite DNA markers to investigate potential fragmentation, genetic drift, and geographic divergence of three populations distributed on the northern, southern, and central portions of the range. Our analyses found that the populations have similar levels of heterozygosity, no significant differences in allelic richness, and significant levels of genetic differentiation. With additional samples from intermediate locations, we would be able to better assess levels of gene flow among these populations. Our current results suggest that these populations do not necessarily require active management intervention. [ABSTRACT FROM AUTHOR]

California voles cause damage to pastures and rangelands, orchards and nurseries, and a wide variety of field crops, including artichokes. The anticoagulant rodenticides (chlorophacinone and diphacinone) typically used for voles are becoming less effective in controlling their populations. Consequently, there is a need to identify new rodenticides that will have a high efficacy on California voles so that agricultural production losses to rodents can be substantially reduced. We tested a new formulation containing two active ingredients (cholecalciferol and diphacinone) as a control method for California voles. Both a pelleted bait and an oil-coated artichoke bract bait were very palatable and efficacious against wild-caught, captive California voles. Efficacy levels of 70%–80% were achieved in the two-choice feeding trials. Additionally, the days-to-death (5–6 days) were less than the time-to-death with anticoagulant only baits. We recommend that a field efficacy study be conducted with cholecalciferol plus diphacinone bait formulations to determine their field performance in the reduction of agricultural damage by California voles. [ABSTRACT FROM PUBLISHER]

The entire range of the critically endangered Amargosa vole (Microtus californicus scirpensis) consists of less than 20 km² of riparian habitat in the Amargosa River drainage of the Mojave Desert in southern California. In September 2010, deformities on ears and chiggers on the ears and genitalia were detected, with some individuals so severely affected that they were missing ear pinnae altogether. Follow-up trapping was performed to document the presence of mites and mite-associated disease, and molecular characterization was performed on the mites. Of 151 Amargosa voles sampled from February to April of 2011, 60 (39.7%) voles had hard orange mites adhered to some part of their bodies, on ears of 46 (76.7%), on genitalia of 11 (18.3%), and near mammary tissue of 13 (21.7%) voles. Gross lesions were not detected on genitalia, but 47% of all individuals examined showed pinnal lesions and deformities, which included alopecia, swelling, marginal necrosis, and ulceration, as well as scarring, scabbing, and loss of pinna mass covering 25-100% of the pinnae. Biopsies revealed parakeratotic hyperkeratosis and acanthosis with diffuse neutrophilic exocytosis and dense necrotic granulocytes in the epidermis and superficial dermis associated with focal erosion and ulceration. In the underlying dermis, there were dense pleocellular inflammatory cell infiltrates composed primarily of necrotic granulocytes and multifocal hemorrhage. In some samples, mite mouthparts could be seen penetrating the superficial epidermis associated with focal necrosis, and mite fragments were found on the surface epidermis and within hair follicles. Microscopic examination of the mites documented that they were a larval trombiculid in the genus Neotrombicula with anatomical features that most closely resemble Neotrombicula microti, based on scutal shape, setation, and texture. PCR of 2 mite pools (each consisting of 3 mites from an individual animal) amplified 331 bp amplicons, which had 92-97% homology with the 18S rRNA gene of Leptotrombidium deliense, although coverage of Trombiculidae in GenBank is sparse. The severity and prevalence of lesions due to this chigger were atypical and distinct. Severe clinical trombiculiasis in this endangered species could negatively impact individual health and fitness. [ABSTRACT FROM AUTHOR]

Volepox virus (VPXV) was first isolated in 1985 from a hind foot scab of an otherwise healthy California vole (Microtus californicus). Subsequent surveys in San Mateo County, CA, revealed serological evidence suggesting that VPXV is endemic to this area, and a second viral isolate from a Pinyon mouse (Peromyscus truei) was collected in 1988. Since then, few studies have been conducted regarding the ecology, pathology, and pathogenicity of VPXV, and its prevalence and role as a potential zoonotic agent remain unknown. To increase our understanding of VPXV disease progression, we challenged 24 California mice (Peromyscus californicus) intranasally with 1.6x10³ PFU of purified VPXV. By day five post infection (pi) we observed decreased activity level, conjunctivitis, ruffled hair, skin lesions, facial edema, and crusty noses. A mortality rate of 54% was noted by day eight pi. In addition, internal organ necrosis and hemorrhages were observed during necropsy of deceased or euthanized animals. Viral loads in tissues (brain, gonad, kidney, liver, lung, spleen, submandibular lymph node, and adrenal gland), bodily secretions (saliva, and tears), and excretions (urine, and/or feces) were evaluated and compared using real time-PCR and tissue culture. Viral loads measured as high as 2x109 PFU/mL in some organs. Our results suggest that VPXV can cause extreme morbidity and mortality within rodent populations sympatric with the known VPXV reservoirs. [ABSTRACT FROM AUTHOR]

Legacy effects occur when particular species or their interactions with others have long-lasting impacts, and they are increasingly recognized as important determinants of ecological processes. However, when such legacy effects have been explicitly explored, they most often involve the long-term direct effects of species on systems, as opposed to the indirect effects. Here, we explore how a legacy of small mammal exclusion on the abundance of a shrub, bush lupine ( Lupinus arboreus), influences the abundance of a native land snail ( Helminthoglypta arrosa) in coastal prairie and dune habitats in central California. The factors that limit populations of land snails are very poorly known despite the threats to the persistence of this group of species. In grasslands, prior vole ( Microtus californicus) exclusion created long-lasting gains in bush lupine abundance, mediated through the seedbank, and was associated with increased snail numbers (10×) compared to control plots where mammals were never excluded. Similar plots in dune habitat showed no difference in snail numbers due to previous mammal exclusion. We tested whether increased competition for food, increased predation, and/or lower desiccation explained the decline in snail numbers in plots with reduced lupine cover. Tethering experiments supported the hypothesis that voles can have long-lasting impacts as ecosystem engineers, reducing woody lupine habitat required for successful aestivation by snails. These results add to a growing list of studies that have found that non-trophic interactions can be limiting to invertebrate consumers. [ABSTRACT FROM AUTHOR]

Zones of contact between divergent biological forms within or between species are critical to the study of speciation. How characters flow across contact zones can be informative of the speciation process. To better understand this phenomenon in a mammal, we investigated cranial shape change in a contact zone between northern and southern phylogeographical groups of California voles ( Microtus californicus). We took 12 linear measurements of skulls, one measurement of the mandible, and coded the presence and absence of two skull foramina for 427 specimens. In multivariate analyses, skulls within parental regions were correctly assigned more than 90% of the time. In the contact zone, 49% were classified as northern and 51% as southern, with a bimodal distribution of posterior probability values. Foraminal patterns in the contact zone were intermediate between northern and southern regions. A cline analysis for coastal populations suggested a similar centre for mitochondrial and nuclear markers, although a centre for the morphological data was offset. Cranial morphology indicates an intermediate area with overlap between the two regions, as suggested by the molecular data, with a pattern distinct from mitochondrial DNA or nuclear DNA markers. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 264-283. [ABSTRACT FROM AUTHOR]

Gene flow links the genetic and demographic structures of species. Despite the fact that similar genetic and demographic patterns shape both local population structure and regional phylogeography, the 2 levels of population connectivity are rarely studied simultaneously. Here, we studied gene flow in the California vole (Microtus californicus), a small-bodied rodent with limited vagility but high local abundance. Within a 4.86-km2 preserve in central California, genetic diversity in 6 microsatellites was high, and Bayesian methods indicated a single genetic cluster. However, individual- based genetic analysis detected a clear signal for isolation-by-distance (IBD) and fine-scale population structure. Mitochondrial cytochrome b sequencing revealed 11 unique haplotypes from the one local area where we sequenced 62 individuals. Phylogeographic analysis of these individuals combined with those sampled from the northern geographic range of the species (the range of the species spans western North America from southern Oregon to northern Mexico and is centered geographically within the state of California) again indicated a lack of structure but a signal for IBD. Patterns of gene flow thus are consistent across spatial scales: while dispersal of the California vole is limited across geographic distance, there is nonetheless considerable movement across the landscape. We conclude that in this species, high local population abundances overcome the potential genetic and demographic effects of limited dispersal. [ABSTRACT FROM AUTHOR]

Abstract: The ability of a taxon to maintain adaptive flexibility in a stochastic environment is a function of the genetic diversity within the population. In small, fragmented populations, genetic variation can become depleted more quickly than in larger, more contiguous populations. Characterizing the patterns of genetic variation and differentiation associated with these processes is an important step in establishing conservation priorities. The Amargosa vole, Microtus californicus scirpensis, is an endangered rodent persisting in the small, fragmented marsh complex surrounding the Amargosa River near Death Valley, California. This naturally patchy system has existed since the end of the Pleistocene (approximately 10,000y.b.p.), however, fragmentation has been exacerbated by recent anthropogenic changes. For this study, I used five nuclear microsatellite loci and the cytochrome-b region of the mitochondrial genome to quantify levels of genetic variation, population substructure, and patterns of gene flow in M.c. scirpensis. These data were compared to a broadly distributed subspecies, Microtus californicus sanctidiegi. Overall levels of nuclear genetic variation were significantly lower in M.c. scirpensis, whether measured in terms of diversity or heterozygosity, compared to more broadly distributed conspecifics. Moreover, only two haplotypes were recovered from the mitochondrial data with over 90% of the observed haplotypes being identical. Despite low genetic diversity, significant genetic subdivision among M.c. scirpensis populations was detected using both pairwise FST and Bayesian clustering methods. Furthermore, isolation by distance analyses reveal that an important landscape feature, ephemeral tributaries, is critical for dispersal among population clusters. Recommendations for conservation management are presented. [ABSTRACT FROM AUTHOR]

Abstract: Quaternary small-mammal fossils are widespread and have served as valuable paleoclimatic proxies through niche-modeling or otherwise relating presence-absence data to climatic data. This paper examines the potential for a new, more resolved type of paleoclimate proxy in the form of Microtus tooth shape, using an abundant California species, Microtus californicus. Geometric morphometrics and partial least squares analyses are used to find geographic signals in the shape of the first lower molar (m1) of this species. M. californicus m1s are relatively straight in the northwest, cooler, moister portion of California and more curved in the southeast, hotter, drier portion of the state. These tooth shape changes may be a result of selection related to different vegetation ultimately controlled by climate, and therefore diet, within the species'' range. The pattern in m1 shape persists when phylogeographic hypotheses are taken into account, indicating that the climate signal is significant independent of intraspecific groupings. This method adds an important new tool to the suite of proxies available to reconstruct past climates at fine spatiotemporal scales and reveals a geographic/climatic signal that correlates with morphological variation across the range of M. californicus. [Copyright &y& Elsevier]

Many vertebrate taxa show genetic differentiation between populations in northern and southern California. This genetic pattern may reflect a common environmental history for these species. For example, a previous study of the California vole (Microtus californicus) showed morphological divergence between populations in northern and southern California and decreased fertility in crosses between the populations. To investigate phylogeographic differences in this species, we assessed variation in mitochondrial and nuclear DNA throughout much of its distribution from Oregon to Baja California. We generated molecular data (mitochondrial cytochrome b and nuclear acid phosphatase V intron [AP5]) for 178 individuals. Examination of these data suggests 2 phylogeographic groups that are largely discordant with the boundaries of 17 currently recognized subspecies. Estimates of pairwise genetic divergence between these groups for cytochrome b are as high as 4.46% uncorrected p. Sequence data for AP5 also indicate a division between populations of M. californicus in northern and southern California. Examination of data from the mitochondrial and nuclear markers together suggests limited gene flow between clades. These data are concordant with other studies that suggest that mountain ranges in California were important in within- and possibly between-species divergence and subsequent contact. The general distribution of each clade, combined with a geographic information system analysis of known capture sites, suggests that clade divergence may be correlated with ecological differences. Our study creates a new framework for reevaluating morphological and ecological diversity in this species, and with more diverse markers, possibly the recognition of 2 species of California voles. [ABSTRACT FROM AUTHOR]

The use of measures of host infestation as a reliable indicator of a flea population size to be used in interspecific comparisons was considered. The abundance of fleas collected from host bodies and collected from host burrows was compared among 55 flea species, controlling for the effect of flea phylogeny. The mean number of fleas on host bodies correlated positively with the mean number of fleas in host burrows/nests both when the entire data pool was analysed and for separate subsets of data on ‘fur’ fleas and ‘nest’ fleas. This was also true for a within-host ( Microtus californicus) between-flea comparison. The results of this study demonstrate that, in general, the index of host body infestation by fleas can be used reliably as an indicator of the entire population size. [ABSTRACT FROM AUTHOR]

We located the endangered rock vole, Microtus chrotorrhinus, at 3 of 59 sites in mixed mesophytic forests in the southern Appalachians. Rock voles were always found within mixed mesophytic habitats characterized by yellow birch, Betula alleghaniensis, rather than mixed mesophytic habitats dominated by other tree species. We compared the tree communities, microhabitat features, and small mammals found within three groups of habitats: sites where M. chrotorrhinus was found, yellow birch habitats where M. chrotorrhinus was not found, and other mixed mesophytic habitats where M. chrotorrhinus was not found. Sites occupied by M. chrotorrhinus had greater amounts of large, rocky substrate, greater incidence of moss, and a more northwest aspect than yellow birch and other mixed mesophytic sites without M. chrotorrhinus. Moreover, sites with rock voles had larger trees and were significantly older than sites without M. chrotorrhinus. Red-backed voles, Clethrionomys gapperi, are readily sampled by live-trap methods and were significantly more abundant at sites with M. chrotorrhinus, and may thus be a promising indicator species. Our results suggest that mixed mesophytic forests, especially older stands dominated by yellow birch and rocky substrate, should be managed with care to preserve M. chrotorrhinus habitat. [ABSTRACT FROM AUTHOR]

I assessed the long-term effects of seasonal inter-habitat movements for a common rodent, Microtus californicus, using matrix models tailored to demographic data obtained on populations living at the marsh–grassland ecotone. Three stochastic models were used to simulate the seasonal and spatial dynamics of this system, with the purpose of determining: (1) the growth rates of populations living in single versus a two-habitat landscape; and (2) if the amount, direction, and seasonality of rodent movements between the two habitats may impact these growth rates. The results indicated that grassland populations could be self-sustaining, but that isolated marsh populations would rapidly decline. Importantly, 98% of the two-habitat simulations yielded growth rates greater than those seen in the grassland model, with populations benefiting the most by movements from marsh into grassland at the end of the dry season. This study demonstrated that movements between marsh ‘sink’ and grassland ‘source’ habitats can potentially increase long-term population growth due to seasonal, inter-habitat differences in resource availability. [Copyright &y& Elsevier]

Space use patterns of California voles are described from intensive live-trapping data obtained during the late breeding season in a peak density year. Operational sex ratios were strongly female biased. Breeding males had mutually exclusive home ranges that overlapped the home ranges of one to several females. The average male home range was larger than the average female home range and tended to encompass female home ranges in their entirety. Breeding females had home ranges that often overlapped extensively with the home ranges of other breeding females. The degree of overlap, however, tended to be either very high or very low, indicating that groups of females may act territorially among themselves. Family groups that may include members of sequential litters formed at high density. Males on experimental removal grids had larger home ranges than males on the high density grids and some became wanderers while most females had home ranges comparable to those on the high density grids. Dispersers onto low density grids were not a random sample of the high density population; large breeding adults and small juveniles were under-represented. No sex differences in dispersal were noted. Immigration into the high density populations was probably negligible. [ABSTRACT FROM AUTHOR]