Peromyscus Eremicus Research Articles

Characterization of a male reproductive transcriptome for Peromyscus eremicus (Cactus mouse).

Rodents of the genus Peromyscus have become increasingly utilized models for investigations into adaptive biology. This genus is particularly powerful for research linking genetics with adaptive physiology or behaviors, and recent research has capitalized on the unique opportunities afforded by the ecological diversity of these rodents. Well characterized genomic and transcriptomic data is intrinsic to explorations of the genetic architecture responsible for ecological adaptations. Therefore, this study characterizes the transcriptome of three male reproductive tissues (testes, epididymis and vas deferens) of Peromyscus eremicus (Cactus mouse), a desert specialist. The transcriptome assembly process was optimized in order to produce a high quality and substantially complete annotated transcriptome. This composite transcriptome was generated to characterize the expressed transcripts in the male reproductive tract of P. eremicus, which will serve as a crucial resource for future research investigating our hypothesis that the male Cactus mouse possesses an adaptive reproductive phenotype to mitigate water-loss from ejaculate. This study reports genes under positive selection in the male Cactus mouse reproductive transcriptome relative to transcriptomes from Peromyscus maniculatus (deer mouse) and Mus musculus. Thus, this study expands upon existing genetic research in this species, and we provide a high quality transcriptome to enable further explorations of our proposed hypothesis for male Cactus mouse reproductive adaptations to minimize seminal fluid loss.

A novel satellite DNA sequence in the Peromyscus genome (PMSat): Evolution via copy number fluctuation

Satellite DNAs (satDNA) are tandemly arrayed repeated sequences largely present in eukaryotic genomes, which play important roles in genome evolution and function, and therefore, their analysis is vital. Here, we describe the isolation of a novel satellite DNA family (PMSat) from the rodent Peromyscus eremicus (Cricetidae, Rodentia), which is located in pericentromeric regions and exhibits a typical satellite DNA genome organization. Orthologous PMSat sequences were isolated and characterized from three species belonging to Cricetidae: Cricetus cricetus, Phodopus sungorus and Microtus arvalis. In these species, PMSat is highly conserved, with the absence of fixed species-specific mutations. Strikingly, different numbers of copies of this sequence were found among the species, suggesting evolution by copy number fluctuation. Repeat units of PMSat were also found in the Peromyscus maniculatus bairdii BioProject, but our results suggest that these repeat units are from genome regions outside the pericentromere. The remarkably high evolutionary sequence conservation along with the preservation of a few numbers of copies of this sequence in the analyzed genomes may suggest functional significance but a different sequence nature/organization. Our data highlight that repeats are difficult to analyze due to the limited tools available to dissect genomes and the fact that assemblies do not cover regions of constitutive heterochromatin.

A High-Resolution Comparative Chromosome Map of Cricetus cricetus and Peromyscus eremicus Reveals the Involvement of Constitutive Heterochromatin in Breakpoint Regions

Compared to humans and other mammals, rodent genomes, specifically Muroidea species, underwent intense chromosome reshuffling in which many complex structural rearrangements occurred. This fact makes them preferential animal models for studying the process of karyotype evolution. Here, we present the first combined chromosome comparative maps between 2 Cricetidae species, Cricetus cricetus and Peromyscus eremicus, and the index species Mus musculus and Rattus norvegicus. Comparative chromosome painting was done using mouse and rat paint probes together with in silico analysis from the Ensembl genome browser database. Hereby, evolutionary events (inter- and intrachromosomal rearrangements) that occurred in C. cricetus and P. eremicus since the putative ancestral Muroidea genome could be inferred, and evolutionary breakpoint regions could be detected. A colocalization of constitutive heterochromatin and evolutionary breakpoint regions in each genome was observed. Our results suggest the involvement of constitutive heterochromatin in karyotype restructuring of these species, despite the different levels of conservation of the C. cricetus (derivative) and P. eremicus (conserved) genomes.

Cacti supply limited nutrients to a desert rodent community.

In the Sonoran Desert, cacti represent a potentially important source of nutrients and water for consumers. Columnar cacti, in particular, produce a large pulse of flowers and succulent fruit during hot summer months. The importance of cactus stems, flowers and fruit to the small mammal community has not been quantified. We exploited natural variation in the carbon isotope (δ(13)C) values of cacti (CAM) versus C3 plants to quantify the relative use of these resources by a diverse desert small mammal community. We also estimated trophic level by measuring nitrogen isotope (δ(15)N) values. We hypothesized that (H1) granivorous heteromyids (kangaroo rats, pocket mice) would exploit the summer pulse of seeds and pulp; (H2) folivorous and omnivorous cactus mice, wood rats, and ground squirrels would exploit cacti stems year-round and seeds when available; and (H3) kangaroo rats and pocket mice would shift from seeds to insects during hot dry months. We found that heteromyids made minimal use of seeds during the period of heavy seed rain. Of the cricetids, only the folivore Neotoma albigula made continuous but highly variable use of cacti resources (annual mean = 32%, range 0-81%), whereas the omnivore Peromyscus eremicus ignored cacti except during the summer, when it exploited seeds and/or fruit pulp (June-July mean = 39%, range 20-64%). We also found little evidence for a shift to greater consumption of insects by heteromyids during the hot dry months. Overall, use of cactus resources by the small mammal community is very limited and highly variable among species.

Éxito reproductivo del gorrión sabanero (Passerculus sandwichensis sanctorum) en el archipiélago San Benito, México

The Savannah sparrow of San Benito (Passerculus sandwichensis sanctorum) is an endemic subspecies of San Benito's archipelago which is listed by the Nom-059-Semarnat-2010 as an endangered subspecies. It has never been studied before. We describe its reproductive biology in the archipelago, and compared with the reproductive success among the populations from the different islands of the archipelago: San Benito Oeste (SBO), San Benito Medio (SBM) and San Benito Este (SBE). The nests were monitored from April to July 2011. The daily survival rate was higher in SBO (0.9779, n= 68), than in SBM (0.9711, n= 34), and in SBE (0.9508, n= 27). However, the reproductive success did not show significant differences among islands (χ2= 0.8586, p> 0.05 gl 2, n= 3). The survival rate of the nesting cycle in the SBO was 56.0%, in SBM was 46.7% and in SBE was 26.9%. The results of this study did not show that the introduced Cactus Mouse in SBO (Peromyscus eremicus cedrocensis) preys on Savannah sparrow nests, although it could be competing for food and space.

Epizootiology of Tacaribe serocomplex viruses (Arenaviridae) associated with neotomine rodents (Cricetidae, Neotominae) in southern California.

The objective of this study was to advance our knowledge of the epizootiology of Bear Canyon virus and other Tacaribe serocomplex viruses (Arenaviridae) associated with wild rodents in California. Antibody (immunoglobulin G [IgG]) to a Tacaribe serocomplex virus was found in 145 (3.6%) of 3977 neotomine rodents (Cricetidae: Neotominae) captured in six counties in southern California. The majority (122 or 84.1%) of the 145 antibody-positive rodents were big-eared woodrats (Neotoma macrotis) or California mice (Peromyscus californicus). The 23 other antibody-positive rodents included a white-throated woodrat (N. albigula), desert woodrat (N. lepida), Bryant's woodrats (N. bryanti), brush mice (P. boylii), cactus mice (P. eremicus), and deer mice (P. maniculatus). Analyses of viral nucleocapsid protein gene sequence data indicated that Bear Canyon virus is associated with N. macrotis and/or P. californicus in Santa Barbara County, Los Angeles County, Orange County, and western Riverside County. Together, analyses of field data and antibody prevalence data indicated that N. macrotis is the principal host of Bear Canyon virus. Last, the analyses of viral nucleocapsid protein gene sequence data suggested that the Tacaribe serocomplex virus associated with N. albigula and N. lepida in eastern Riverside County represents a novel species (tentatively named "Palo Verde virus") in the genus Arenavirus.

Characterization of the transcriptome, nucleotide sequence polymorphism, and natural selection in the desert adapted mouse Peromyscus eremicus.

As a direct result of intense heat and aridity, deserts are thought to be among the most harsh of environments, particularly for their mammalian inhabitants. Given that osmoregulation can be challenging for these animals, with failure resulting in death, strong selection should be observed on genes related to the maintenance of water and solute balance. One such animal, Peromyscus eremicus, is native to the desert regions of the southwest United States and may live its entire life without oral fluid intake. As a first step toward understanding the genetics that underlie this phenotype, we present a characterization of the P. eremicus transcriptome. We assay four tissues (kidney, liver, brain, testes) from a single individual and supplement this with population level renal transcriptome sequencing from 15 additional animals. We identified a set of transcripts undergoing both purifying and balancing selection based on estimates of Tajima’s D. In addition, we used the branch-site test to identify a transcript—Slc2a9, likely related to desert osmoregulation—undergoing enhanced selection in P. eremicus relative to a set of related non-desert rodents.

LINE-1 retrotransposons: from 'parasite' sequences to functional elements.

Long interspersed nuclear elements-1 (LINE-1) are the most abundant and active retrotransposons in the mammalian genomes. Traditionally, the occurrence of LINE-1 sequences in the genome of mammals has been explained by the selfish DNA hypothesis. Nevertheless, recently, it has also been argued that these sequences could play important roles in these genomes, as in the regulation of gene expression, genome modelling and X-chromosome inactivation. The non-random chromosomal distribution is a striking feature of these retroelements that somehow reflects its functionality. In the present study, we have isolated and analysed a fraction of the open reading frame 2 (ORF2) LINE-1 sequence from three rodent species, Cricetus cricetus, Peromyscus eremicus and Praomys tullbergi. Physical mapping of the isolated sequences revealed an interspersed longitudinal AT pattern of distribution along all the chromosomes of the complement in the three genomes. A detailed analysis shows that these sequences are preferentially located in the euchromatic regions, although some signals could be detected in the heterochromatin. In addition, a coincidence between the location of imprinted gene regions (as Xist and Tsix gene regions) and the LINE-1 retroelements was also observed. According to these results, we propose an involvement of LINE-1 sequences in different genomic events as gene imprinting, X-chromosome inactivation and evolution of repetitive sequences located at the heterochromatic regions (e.g. satellite DNA sequences) of the rodents' genomes analysed.

Permeability of Roads to Movement of Scrubland Lizards and Small Mammals

A primary objective of road ecology is to understand and predict how roads affect connectivity of wildlife populations. Road avoidance behavior can fragment populations, whereas lack of road avoidance can result in high mortality due to wildlife-vehicle collisions. Many small animal species focus their activities to particular microhabitats within their larger habitat. We sought to assess how different types of roads affect the movement of small vertebrates and to explore whether responses to roads may be predictable on the basis of animal life history or microhabitat preferences preferences. We tracked the movements of fluorescently marked animals at 24 sites distributed among 3 road types: low-use dirt, low-use secondary paved, and rural 2-lane highway. Most data we collected were on the San Diego pocket mouse (Chaetodipus fallax), cactus mouse (Peromyscus eremicus), western fence lizard (Sceloporus occidentalis), orange-throated whiptail (Aspidoscelis hyperythra), Dulzura kangaroo rat (Dipodomys simulans) (dirt, secondary paved), and deer mouse (Peromyscus maniculatus) (highway only). San Diego pocket mice and cactus mice moved onto dirt roads but not onto a low-use paved road of similar width or onto the highway, indicating they avoid paved road substrate. Both lizard species moved onto the dirt and secondary paved roads but avoided the rural 2-lane rural highway, indicating they may avoid noise, vibration, or visual disturbance from a steady flow of traffic. Kangaroo rats did not avoid the dirt or secondary paved roads. Overall, dirt and secondary roads were more permeable to species that prefer to forage or bask in open areas of their habitat, rather than under the cover of rocks or shrubs. However, all study species avoided the rural 2-lane highway. Our results suggest that microhabitat use preferences and road substrate help predict species responses to low-use roads, but roads with heavy traffic may deter movement of a much wider range of small animal species.

Comparison of Distribution and Habitat Characteristics between an Endemic and a Wide-Ranging Cryptic Species ofPeromyscuson the Baja California Peninsula

Peromyscus eva and Peromyscus fraterculus are 2 morphologically similar species of the Peromyscus eremicus group occurring on the Baja California Peninsula. Due to the similarity between these 2 species, their ranges have been greatly confused; consequently, the specific habitat characteristics for each group are not well known. The goal of this study was to assess distribution ranges and characteristics of preferred habitats for P. eva and P. fraterculus in more detail. We identified taxonomy of individuals by evaluating genetic patterns produced by restriction fragment length polymorphisms (RFLPs). We evaluated the banding pattern generated by Alu I and Bam HI restriction enzymes in an 850-bp cytochrome b fragment. Consistent differences in number and size of fragments allowed for discrimination of individuals to species. The heterogeneity and evenness indexes showed that the microhabitat of P. fraterculus contained less-diverse soil types and is more homogeneous than the microhabitat of P. eva. In the state of Baja California Sur, P. eva occurs exclusively in the flat areas along the Pacific coast from the Vizcaino Desert to the south, including Margarita Island, with one small population in the Loreto area adjacent to Carmen Island. The habitats occupied by P. eva were heterogeneous (areas with friable, soft sandy soil and a low percentage of small stones). Peromyscus fraterculus occurs mostly in Baja California Norte, with some populations distributed in Baja California Sur, particularly in the western areas of the Vizcaino Desert along the mountain range, in the gulf side of the peninsula south of the city of La Paz, and in a small area on the eastern side of Sierra de Las Cruces. This species was mostly found on hard soil with high medium-size stone content.

Hidden heterochromatin: characterization in the Rodentia species Cricetus cricetus, Peromyscus eremicus (Cricetidae) and Praomys tullbergi (Muridae)

The use of in situ restriction endonuclease (RE) (which cleaves DNA at specific sequences) digestion has proven to be a useful technique in improving the dissection of constitutive heterochromatin (CH), and in the understanding of the CH evolution in different genomes. In the present work we describe in detail the CH of the three Rodentia species, Cricetus cricetus, Peromyscus eremicus (family Cricetidae) and Praomys tullbergi (family Muridae) using a panel of seven REs followed by C-banding. Comparison of the amount, distribution and molecular nature of C-positive heterochromatin revealed molecular heterogeneity in the heterochromatin of the three species. The large number of subclasses of CH identified in Praomys tullbergi chromosomes indicated that the karyotype of this species is the more derived when compared with the other two genomes analyzed, probably originated by a great number of complex chromosomal rearrangements. The high level of sequence heterogeneity identified in the CH of the three genomes suggests the coexistence of different satellite DNA families, or variants of these families in these genomes.

Different evolutionary trails in the related genomes Cricetus cricetus and Peromyscus eremicus (Rodentia, Cricetidae) uncovered by orthologous satellite DNA repositioning

Constitutive heterochromatin comprises a substantial fraction of the eukaryotic genomes and is mainly composed of tandemly arrayed satellite DNAs (satDNA). These repetitive sequences represent a very dynamic and fast evolving component of genomes. In the present work we report the isolation of Cricetus cricetus (CCR, Cricetidae, Rodentia) centromeric repetitive sequences from chromosome 4 (CCR4/10sat), using the laser microdissection and laser pressure catapulting procedure, followed by DOP-PCR amplification and labelling. Physical mapping by fluorescent in situ hybridisation of these sequences onto C. cricetus and another member of Cricetidae, Peromyscus eremicus, displayed quite interesting patterns. Namely, the centromeric sequences showed to be present in another C. cricetus chromosome (CCR10) besides CCR4. Moreover, these almost chromosome-specific sequences revealed to be present in the P. eremicus genome, and most interestingly, displaying a ubiquitous scattered distribution throughout this karyotype. Finally and in both species, a co-localisation of CCR4/10sat with constitutive heterochromatin was found, either by classical C-banding or C-banding sequential to in situ endonuclease restriction. The presence of these orthologous sequences in both genomes is suggestive of a phylogenetic proximity. Furthermore, the existence of common repetitive DNA sequences with a different chromosomal location foresees the occurrence of an extensive process of karyotype restructuring somehow related with intragenomic movements of these repetitive sequences during the evolutionary process of C. cricetus and P. eremicus species.

Assessment of mercury concentrations in small mammals collected near Las Vegas, Nevada, USA

Mercury concentrations in liver and hair tissue were determined for five species of small mammals captured near Las Vegas, Nevada, USA. These data were then used to evaluate the suitability of using hair as a noninvasive technique for determining body burdens of mercury. A total of 104 small mammals were captured and analyzed; four main species were examined and included: Dipodomys merriami, Chaetodipus penicillatus, Peromyscus eremicus, and Neotoma lepida. Mean mercury concentrations were highest in N. lepida, followed by D. merriami, C. penicillatus, and P. eremicus respectively. Positive associations were found between hair and liver taken from D. merriami (r = 0.647) and C. penicillatus (r = 0.533) indicating that hair may be a suitable indicator of body burdens in these two species.

P16: Aneuploidy-screening in single cells by a rapid comparative genomic hybridization protocol for prenatal diagnostics

Constitutive heterochromatin comprises a substantial fraction of the eukaryotic genomes and is mainly composed of tandemly arrayed satellite DNAs (satDNA). These repetitive sequences represent a very dynamic and fast evolving component of genomes. In the present work we report the isolation of Cricetus cricetus (CCR, Cricetidae, Rodentia) centromeric repetitive sequences from chromosome 4 (CCR4/10sat), using the laser microdissection and laser pressure catapulting procedure, followed by DOP-PCR amplification and labelling. Physical mapping by fluorescent in situ hybridisation of these sequences onto C. cricetus and another member of Cricetidae, Peromyscus eremicus, displayed quite interesting patterns. Namely, the centromeric sequences showed to be present in another C. cricetus chromosome (CCR10) besides CCR4. Moreover, these almost chromosome-specific sequences revealed to be present in the P. eremicus genome, and most interestingly, displaying a ubiquitous scattered distribution throughout this karyotype. Finally and in both species, a co-localisation of CCR4/10sat with constitutive heterochromatin was found, either by classical C-banding or C-banding sequential to in situ endonuclease restriction.The presence of these orthologous sequences in both genomes is suggestive of a phylogenetic proximity. Furthermore, the existence of common repetitive DNA sequences with a different chromosomal location foresees the occurrence of an extensive process of karyotype restructuring somehow related with intragenomic movements of these repetitive sequences during the evolutionary process of C. cricetus and P. eremicus species.

Small Mammal Community Responses to a Wildfire on a Central Arizona Sky Island

In April 1996, a wildfire (Lone Fire) denuded >90% of the vegetation in a 237-km2 area on the Four Peaks “sky island” in the Mazatzal Mountains in central Arizona. We trapped small mammals from 1997 to 1999 in both burned and unburned interior chaparral and Madrean evergreen forest vegetation to investigate differences in small mammal communities post-fire. In 15,173 live trap nights and 26,214 pitfall trap nights overall species richness (P=0.76) and mammal abundance did not differ (P=0.53) among vegetation types. However, species richness differed (P=0.04) among seasons. We found that a minimum of four small mammal species were influenced by fire. Dipodomys merriami and D. ordii abundances were higher (P=0.011 and P=0.064, respectively) in burned chaparral than in unburned chaparral, while Chaetodipus baileyi abundances were higher (P=0.05) in unburned chaparral than burned chaparral. Peromyscus eremicus differed seasonally (χ2=9.22, P=0.056) as they were captured more as post-fire time increased. Implications of catastrophic fires with high vegetation mortality and management considerations are discussed.

Social structure influences effects of pair-housing on wound healing

Chronic stress or noxious stimuli delay wound healing in humans and rodents. The effects of stress on wound healing appear to be mediated by the hypothalamic–pituitary–adrenal (HPA) axis and, in particular, increases in corticosteroids. As previously shown, positive social interaction faciltiates wound healing through suppression of corticosteroids. In the present study, we investigated the effects of pair-housing on wound healing and corticosteroid concentrations in three mouse species, the monogamous Peromyscus californicus, the facultative-monogamous Peromyscus eremicus, and the polygynous Peromyscus leucopus. Pair-housed P. californicus and P. eremicus had significantly smaller wounds than socially isolated cohorts. However, wound healing in P. leucopus was not affected by housing condition. P. californicus and P. eremicus mice that were pair-housed for 2 weeks, then separated from their partners 48 h prior to wounding also had wounds comparable to socially isolated mice. The benefits of social housing diminished when P. californicus and P. eremicus pairs were prevented from interacting physically via a double screen barrier. Two hours of daily restraint did not affect basal corticosterone concentrations or wound healing in either P. californicus or P. eremicus. In contrast, restraint facilitated wound healing in P. leucopus. Taken together, these data suggest that social contact facilitates wound healing in two monogamous, but not a polygynous, mouse species.

Use of corridor-like landscape structures by bird and small mammal species

We investigated the use of corridor-like structures by birds and rodents in coastal San Diego County, California, USA, in areas characterized by dense residential development and small remnant habitat fragments. In 1992 and 1993 we compared the use of remnant strips of coastal sage scrub habitat and revegetated highway rights-of-way (ROW) with that of larger remnant patches of coastal sage scrub habitat to which these strips were connected. Using live trapping we compared rodent species composition, percent of females reproducing, and recapture frequency among the three site types. Rodent species richness did not differ significantly among the three site types. One species, Peromyscus eremicus was significantly more abundant in ROW sites, while several other species, Rheithrodontomys californicus, Chaetodipus californicus and C. fallax showed a similar, though non-significant trend. Peromyscus californicus was most abundant in remnant strips while Neotoma fuscipes used ROW sites less than remnant strips or patches. No significant differences were detected among the three site types in recapture frequency or proportion of females in reproductive condition. Common bird species were a priori divided into two categories based on previous research in this region: fragmentation-sensitive and fragmentation-tolerant. Species richness in remnant strips of habitat was similar to that in remnant patches for both categories of species. Species richness of the fragmentation-sensitive species was significantly lower in ROW sites than in remnant strips or patches by a factor of 4–10. Species richness in fragmentation-tolerant species was significantly lower in ROW sites in 1993 by less than a factor of two. The greater reduction in fragmentation-sensitive species suggests they have more stringent corridor requirements than do fragmentation-tolerant species. The species richness per site for fragmentation-sensitive bird species was significantly correlated with the percent cover of native shrubs in 1993 in patch and remnant strip sites. Fragmentation-tolerant bird species showed no consistent trend with shrub cover. Rodent species richness trended higher with increasing shrub cover in five of six site-type/year combinations, but none of the correlations were significant. Within the range of width and length examined there was no correlation between bird or rodent species richness and length or width of these corridor-like structures. These results indicate that remnant strips of habitat and revegetated highway ROW have potential to serve as habitat linkages for native rodents and fragmentation-tolerant bird species, but only remnant habitat strips appear suitable for fragmentation-sensitive bird species.

Comparative Phylogeography of Baileys' Pocket Mouse (Chaetodipus baileyi) and the Peromyscus eremicus Species Group: Historical Vicariance of the Baja California Peninsular Desert

Phylogenetic analysis of 699 bp of the mitochondrial DNA (mtDNA) COIII and 450 bp of the cytochrome b genes among 14 species of coarse-haired pocket mice (Heteromyidae: Chaetodipus) corroborated previous indications that genetic divergence between species and species groups within the genus is generally very high, suggesting old times of divergence, and that the nominal species C. baileyi represents a highly divergent lineage within the genus, with no closely related extant sister species. Analysis of phylogeographic structure among 51 individuals from 12 localities throughout the geographic range of C. baileyi revealed three geographically separate mtDNA haplotype lineages. The oldest split separates populations east and west of the Colorado River, a pattern that is congruent with chromosomal and allozyme electrophoretic evidence. We consider the western populations to represent a distinct species, C. rudinoris. Within C. rudinoris, mtDNA haplotypes are further subdivided into northern and southern lineages along the Baja California Peninsula. Comparison of phylogeographic structure in the baileyi species group and the codistributed Peromyscus eremicus species group implies two points of codivergence and thus supports two historical vicariance hypotheses proposed for biotas distributed across the peninsular and continental warm deserts: a late Neogene (3 Ma) northern extension of the Sea of Cortéz and a mid-Pleistocene (1 Ma) midpeninsular seaway across Baja California.

Phylogeography and Systematics of the Peromyscus eremicus Species Group and the Historical Biogeography of North American Warm Regional Deserts

Phylogeographic relationships among 26 populations from throughout the geographic range of the Peromyscus eremicus species group are described based on sequence data for a 699-bp fragment of the mitochondrial DNA COIII gene. Distance, maximum-likelihood, and maximum-parsimony analyses of phylogenetic trees generated under four separate character-weighting strategies and representing five alternative biogeographic hypotheses revealed the existence of a cryptic species (Peromyscus fraterculus, previously included under P. eremicus) on the Baja California Peninsula and adjacent southwestern California and two distinct forms of P. eremicus, one from the Mojave, Sonoran, and northwestern Chihuahuan regional deserts (West) and one from the remainder of the Chihuahuan Desert (East). Distinctiveness of P. fraterculus is supported by previous morphometric and allozyme analyses, including comparisons with neighboring P. eremicus and parapatric P. eva, with which P. fraterculus shares a sister taxon relationship. Divergence of the eva + fraterculus, West + East eremicus, and P. merriami haplotype lineages likely occurred in the late Neogene (3 Ma), in response to northern extension of the Sea of Cortéz and elevation of the Sierra Madre Occidental; divergence of eva from fraterculus is concordant with the existence of a trans-Peninsular seaway during the Pleistocene (1 Ma); and divergence of West from East eremicus occurred during the Pleistocene pluvial–interpluvial cycles, but well before the Wisconsinan glacial interval. The sequence of divergence within the eremicus species group and causal association of geological events of the Neogene and Holocene provide a working hypothesis against which phylogeographic patterns among other arid-adapted species of the warm regional deserts of North America may be compared.

Arenavirus antibody in rodents indigenous to coastal southern California.

The purpose of this study was to extend our knowledge on the geographic and natural rodent host ranges of New World arenaviruses in California. Sera from 1,094 sigmodontine and 112 murine rodents were tested for antibody against Whitewater Arroyo and Amapari viruses. Antibody was found in 55 (4.6%) of the 1,206 rodents: 4 from northwestern San Diego County, 3 from Los Angeles County, and 48 from Orange County. The antibody-positive rodents included 8 (7.8%) of 103 Neotoma fuscipes, 1 (0.6%) of 180 Neotoma lepida, 1 (3.1%) of 32 Peromyscus boylii, 8 (11.0%) of 73 Peromyscus californicus, 1 (1.2%) of 85 Peromyscus eremicus, 30 (8.5%) of 353 Peromyscus maniculatus, and 6 (2.2%) of 268 Reithrodontomys megalotis. This study provides the first evidence that New World arenaviruses occur in Los Angeles and Orange counties and northwestern San Diego County, and the first evidence that Peromyscus and Reithrodontomys species are naturally infected with New World arenaviruses.