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We examined 590 specimens of Reithrodontomys from 95 localities in the state of Mexico. Four species of the subgenus Reithrodontomys and 1 of the subgenus Aporodon were identified. The former subgenus included R. chrysopsis, R. sumichrasti, R. megalotis, and R. fulvescens, which has 2 subspecies—R. f. toltecus and R. f. mustelinus—in the state. The representative of the subgenus Aporodon is R. microdon wagneri, which is recorded for the first time in the state. We give information on taxonomy, morphometrics, reproduction, habitat characteristics, and related fauna. A discriminant analysis correctly classified 100% of specimens from the 6 taxa with 5 canonical variates, and accounted for 96.1% of the variance with the first 3 canonical variates.

Barn Owls have a flexible diet for catching their prey based on availability. However, little has been explored about the age class distribution of their main prey. In this work we analyzed the prey diversity, niche width and age class frequency of their main prey from pellets of Barn Owls ( Tyto alba ) found in a cave surrounded by oak forest in Central Oaxaca, Mexico. From entire and disintegrated pellets, material of 12 prey taxa was recorded, mainly mammals (83.33%). Based on the analysis of 69 pellets, 133 individuals comprising six mammal species were found, in which Heteromys irroratus and Reithrodontomys sp. represented 68.84%. In both species, age classes III (subadults) and IV (adults) were the most frequent. The indexes of trophic niche breadth and prey diversity were moderate, denoting a specialist diet. Based on our results and literature review, we found that genera Heteromys, Reithrodontomys, Peromyscus, Sigmodon, Dipodomys, Perognatus and Chaetodipus are the main prey of Barn Owls in Mexico. Keywords: diet, Heteromys irroratus, trophic niche.

We report the karyotypes of Reithrodontomys hirsutus and R. mexicanus from Oaxaca and Puebla, Mexico, and R. sumichrasti from Puebla and Veracruz, Mexico; the first is described for the first time and the latter 2 represent karyotypic variants from localities different from those previously reported. Our findings confirm the complex chromosomal evolution that has occurred within the genus Reithrodontomys and support molecular data indicating that an undescribed species inhabits the highlands of the Sierra Madre Oriental in Mexico. We also document chromosomal variation within R. sumichrasti congruent with phylogenetic patterns reported previously.

Environmental stochasticity in vital rates influences the dynamics of structured populations. Stochastic models of population dynamics often assume that vital rates vary independently, an assumption that may be violated in many populations. We estimated the survival of three species of grassland rodents – deer mouse Peromyscus maniculatus, white-footed mouse Peromyscus leucopus and western harvest mouse Reithrodontomys megalotis– using a long-term dataset. We used these data to assess the level of cross correlation and autocorrelation in stage-specific survival rates and the correlation between survival and selected environmental variables. We found little evidence of correlation among survival estimates in any species or correlation between survival and environmental variables. In contrast to other species in the region, our analyses suggest that survival rates in deer mice, white-footed mice and western harvest mice vary independently throughout the year.

To minimize impact on small mammals while preventing invasion of woody vegetation, we mowed alternating 15-m strips on our area. We then compared numbers and movements of 5 species of rodents on mowed and unmowed strips. Numbers of hispid cotton rats (Sigmodon hispidus) and prairie voles (Microtus ochrogaster) were reduced temporarily in the mowed strips, whereas numbers of white-footed mice (Peromyscus leucopus), deer mice (P. maniculatus), and western harvest mice (Reithrodontomys megalotis) did not change significantly. Movements of cotton rats, prairie voles, and harvest mice across mowed strips were reduced, whereas movements within unmowed strips were relatively unaffected, decreasing only for white-footed and harvest mice in 1 of 2 temporal replicates. Changes in numbers and movements were of short duration, and hence mowing narrow strips when vegetation could recover rapidly had little sustained impact on this rodent community.

We estimated phylogenetic relationships among 16 species of harvest mice using sequences from the mitochondrial cytochrome b (cyt b) gene. Gene phylogenies constructed using maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) optimality criteria were largely congruent and arranged taxa into two groups corresponding to the two recognized subgenera (Aporodon and Reithrodontomys). All analyses also recovered R. mexicanus and R. microdon as polyphyletic, although greater resolution was obtained using ML and BI approaches. Within R. mexicanus, three clades were identiWed with high nodal support (MP and ML bootstrap, Bremer decay and Bayesian posterior probabilities). One represented a subspecies of R. mexicanus from Costa Rica (R. m. cherrii) and a second was distributed in the Sierra Madre Oriental of Mexico. The third R. mexicanus clade consisted of mice from southern Mexico southward to South America. Polyphyly between the two moieties of R. microdon corresponded to the Isthmus of Tehuantepec in southern Mexico. Populations of R. microdon microdon to the east of the isthmus (Chiapas, Mexico) grouped with R. tenuirostris, whereas samples of R. m. albilabris to the west in Oaxaca, Mexico, formed a clade with R. bakeri. Within the subgenus Reithrodontomys, all analyses recovered R. montanus and R. raviventris as sister taxa, a Wnding consistent with earlier studies based on allozymes and cyt b data. There was also strong support (ML and BI criteria) for a clade consisting of ((R. megalotis, R. zacatecae) (R. sumichrasti)). In addition, cytb gene phylogenies (MP, ML, and BI) recovered R. fulvescens and R. hirsutus (ML and BI) as basal taxa within the subgenus Reithrodontomys. Constraint analyses demonstrated that tree topologies treating the two subgenera (Aporodon and Reithrodontomys) as monophyletic (ML criterion) was signiWcantly better (p > 0.036) and supported polyphyly of R. mexicanus (both ML and MP criteria – p > 0.013) and R. microdon (MP criterion only for certain topologies; p > 0.02). Although several species-level taxa were identiWed based on multiple, independent data sets, we recommended a conservative approach which will involve thorough analyses of museum specimens including material from type localities together with additional sampling and data from multiple, nuclear gene markers.  2005 Elsevier Inc. All rights reserved.

We compared the initial effects of four forest regeneration treatments (single-tree selection, group selection, shelterwood, and clearcut), and unharvested controls (mature, second-growth forest) on relative abundance of small mammals and small-mammal habitat throughout the Ouachita Mountains of western Arkansas and eastern Oklahoma. We compared small-mammal capture rates in 20 forest stands (4 replicates of 5 treatments) for 2 years prior to harvest treatments, and 1.5, 3.5, and 5.5 years after treatment. We also examined relationships among small mammals, treatments, and habitat conditions. Before harvest, all stands where characterized by high basal areas (BA), little understory vegetation, and low small-mammal capture rates. Compared with pre-harvest numbers, the number of individuals captured increased nearly five-fold in treated stands 1.5 years after harvest. After harvest, capture rates for all taxa combined were significantly greater in harvested stands (regardless of treatment) than in unharvested controls. Fulvous harvest mice (Reithrodontomys fulvescens) capture rates were greatest in clearcuts. Fulvous harvest mice, cotton rats (Sigmondon hispidus), and pine voles (Microtus pinetorum) were associated with abundant herbaceous vegetation in the understory and low BA. Eastern woodrats (Neotoma floridana), golden mice (Ochrotomys nuttalli), and Peromyscus spp. were associated with moderate to dense woody vegetation in the understory and intermediate BA levels. No taxon of terrestrial small mammal was captured exclusively in unharvested stands; most taxa we captured appear to be either disturbance-adapted or tolerant to disturbances from timber harvest.

We conducted a mark-recapture experiment to examine population dynamics of the fulvous harvest mouse (Reithrodontomys fulvescens) and plains harvest mouse (R. montanus) in response to low-level nitrogen amendments (16.4 kg N/ha/y) in an old-field grassland. The experimental design consisted of 16, 0.16-ha plots with four replicates of each treatment combination (fenced, nitrogen amendment; unfenced, nitrogen amendment; fenced, control; unfenced, control). We predicted that densities, survival, and transition probabilities would be greater for both species on nitrogen-amended plots because of greater aboveground biomass (i.e., enhanced concealment from predators). We observed no distinct patterns in survival or transition probabilities of R. fulvescens or R. montanus with regard to treatments. Although population densities of R. fulvescens did not exhibit any distinct patterns with regard to treatments, densities of R. montanus tended to be highest on nitrogen plots, but lowest on nitrogen-fenced ...

We applied a rigorous, quantitative methodology to the analysis of local-scale spatial clustering of multiple murid mice (brush mice, Peromyscus boylii; deer mice, P. maniculatus; pinon mice, P. truei; western harvest mice, Reithrodontomys megalotis) infected or uninfected with hantaviruses. Rodents were sampled longitudinally from 1994 to 2001 on 23 trapping webs at 10 locations in the southwestern United States. This study provided an opportunity to apply meta-analysis techniques to an important ecological question. There were sufficient captures by species on 199 occasions (three consecutive nights) to compare general use of space using multi-response permutation procedures (MRPP). The MRPP results were then used in meta-analyses by species to determine if overall effects of spatial clustering of hantavirus-infected mice as well as categorical effects (elevation, season, site, and state) were present. Based on MRPP analyses, overall spatial clustering of hantavirus-infected mice was most pronounced for brush mice, followed by the deer mouse. Meta-analyses indicated significant overall effects of spatial clustering and varying categorical effects (elevation, season, site, state) of infected mice for each species compared. The overlapping space use by rodents might be an important factor affecting the local transmission of several hantaviruses.

This paper reports mites and ticks of small mammals in the states of Baja California Sur, Chiapas, Jalisco, Michoacan, Oaxaca, Puebla, San Luis Potosi and Veracruz in Mexico. Genera of small mammals sampled were: Balantiopteris, Chaetodipus, Cryptotis, Habromys, Heteromys, Liomys, Marmosa, Megadontomys, Microtus, Nyctomys, Oryzomys, Osgoodomys, Peromyscus, Reithrodontomys, Sigmodon and Sorex. The recorded mites belonged to 15 families but Glycyphagidae, Laelapidae, Listrophoridae and Trombiculidae included most species.

We assessed the influence of 19 microhabitat factors on the distribution and abundance of small mammals at 60 plots across Fort Sill Military Reservation in Comanche County, Oklahoma. Trapping took place each spring from 1989 to 1992. We collected 15 small mammal species and used 10 of these (Chaetodipus hispidus, Cryptotis parva, Microtus ochrogaster, Neotoma floridana, Peromyscus attwateri, P. leucopus, P. maniculatus, Reithrodontomys fulvescens, R. montanus, and Sigmodon hispidus) in our analyses. Microhabitat variables for each mammal species were evaluated as unweighted measures based on the presence or absence of each species at a plot and as weighted measures based on the abundance of each species at each plot. Both weighted and unweighted data were subjected to cluster analysis, principal components analysis, and discriminant-function analysis. General trends of the microhabitat affinities of species in each cluster were summarized on principal components. Four species (C. hispidus, N. floridana, P. attwateri, and P. leucopus) occupied barren or rocky areas with a tall herbaceous or woody canopy, and 6 species (C. parva, M. ochrogaster, P. maniculatus, R. fulvescens, R. montanus, and S. hispidus) preferred open grassy areas. Weighted discriminant analysis produced better predictive accuracy (75% correctly classified) than the unweighted data (63% correctly classified). Total number of broadleaf trees and rocky ground cover were the most important factors in discriminating among groups.

Studies on the effects of anthropogenic contamination on wildlife have largely been focused at the individual level. Biomarkers have been used to monitor changes in the health of individuals exposed to contaminants; however, little attention has been given to the effects of chronic exposure at the population or community levels. We studied rodent assemblages from uncontaminated (reference) sites (n = 5) and abandoned petrochemical landfarms (n = 5) in Oklahoma to investigate potential alterations in community structure and composition. Rodent assemblages inhabiting landfarms had lower species diversity, lower richness, and a more even distribution of individuals across species. Reference sites showed typical rodent assemblage structure dominated by hispid cotton rats (Sigmodon hispidus) and fulvous harvest mice (Reithrodontomys fulvescens). Assemblages inhabiting landfarms also were dominated by cotton rats; however, harvest mice were replaced by deer mice (Peromyscus maniculatus) on two landfarms. Contam...

DNA sequences obtained from the mitochondrial cytochrome-b gene were used to evaluate phylogenetic relationships among 15 genera of putative neotomine–peromyscine rodents. Tree topologies obtained from maximum likelihood and Bayesian analyses revealed 4 primary clades that, in general, conform to the 4 tribes proposed by Carleton (1980). The Peromyscini (Megadontomys, Ochrotomys, Osgoodomys, Peromyscus, and Reithrodontomys) was sister to the Neotomini (Hodomys, Neotoma, Onychomys, and Xenomys). These 2 clades were then joined by the Baiomyini (Baiomys and Scotinomys) and Tylomyini (Nyctomys, Ototylomys, and Tylomys). The most apparent departure from previously proposed arrangements involved the placement of Onychomys in the Neotomini instead of the Peromyscini.

We tested whether differences in composition and nutrients of diet explained higher density of Peromyscus aztecus in mature cloud forest and higher density of Reithrodontomys fulvescens in disturbed cloud forest. P. aztecus ate dicot leaves, stems, fruit, and seeds in mature cloud forest and dicot leaves, stems, and seeds, and monocot seeds and insects during the dry-hot season in disturbed cloud forest. R. fulvescens ate dicot leaves, stems, fruit, and seeds in mature cloud forest but monocots and insects during the hot season; dicot leaves, stems, and seeds were eaten in disturbed cloud forest. The diet of P. aztecus contained more protein and soluble carbohydrates in disturbed cloud forest where rodent density was lower; the diet of R. fulvescens contained more protein, lipid, soluble carbohydrate, Na, Mg, and P in mature cloud forest where density was lower. Nutrient differences resulted from R. fulvescens eating more monocots and dicot fruit, P. aztecus eating more monocot seeds and less dicot fruit, and both species eating more insects. Differences in composition or nutrient content of diet did not explain between-habitat differences in demography because nutrients in diet were higher in habitat of lower rodent abundance, suggesting other factors must be considered.

Five hundred fifty-six samples representing 24 species of small mammals (two species of marsupials and 22 rodents) were collected in Panama between February 2000 and July 2002. The samples were examined for antibodies to hantaviruses by means of enzyme-linked immunosorbent assay or immunoblot assays. The serologic results indicated that several rodent species might act as hantaviral reservoirs in Panama: Costa Rican pygmy rice rat (Oligoryzomys fulvescens costaricensis), four positive of 72 tested (5.6%); Cherrie's cane rat (Zygodontomys brevicauda cherriei), five of 108 (4.6%); Mexican deer mouse (Peromyscus mexicanus), one of 22 (5%); Mexican harvest mouse (Reithrodontomys mexicanus), one of seven (14%); Chiriquí harvest mouse (Reithrodontomys creper), one of two (50%); and Sumichrast's harvest mouse (Reithrodontomys sumichrasti), three of four (75%). Hantavirus infection in Peromyscus mexicanus and the three species of Reithrodontomys was caused by Rio Segundo hantavirus, a species of virus not previously reported from Panama. At least three hantaviruses, therefore, are known to infect populations of wild rodents in the country. However, given the total number of animals tested, the role of these rodent species in the epidemiology and epizootiology of hantavirus infections remains unclear.

New fossiliferous localities in the Borchers Badlands of southwestern Kansas add to our knowledge of rodent community change across the Plio-Pleistocene and Blancan-Irvingtonian boundaries. We report fossil rodents from ten local faunas in the Badlands that range stratigraphically from beneath the Huckleberry Ridge ash (2.10 Ma [million years ago]) to a level just beneath the Cerro Toledo B ash (1.23–1.47 Ma). The late Blancan Borchers local fauna (l.f.), includes the Meade Basin highest stratigraphic datum (HSD) for the following taxa that characterize or are found in earlier Blancan faunas:Alilepus, Geomys quinni, Sigmodon minor, andGeochelone. Borchers currently also has the HSDs forReithrodontomys pratincolaandOndatra zibethicus lidahoensis, but the prior temporal distribution of these taxa in the Meade Basin is unknown. The stratigraphically lowest Pleistocene (Irvingtonian) l.f. in the Badlands, Nash 72, includes the lowest stratigraphic datum (LSD) forCynomys, Reithrodontomys moorei, Microtus, andMictomys kansasensis, all of which are found above Nash 72 and beneath the Cerro Toledo B ash.Prodipodomysis last seen at Nash 72, andSigmodon curtisiis first encountered at Short Haul, a locality slightly younger than Nash 72. A preliminary hypothesis of age based on stratigraphic position places the Nash 72 l.f. at about 1.80 Ma, suggesting that this fauna and the genusMicrotusmay characterize both the Plio-Pleistocene and Blancan-Irvingtonian boundaries in the Borchers Badlands.

Loblolly pine ( Pinus taeda L.) regeneration or establishment impacts a large area over the southern US but few studies have examined the microhabitat relationship of small mammals on young pine stands. We collected over 1600 small mammals on natural and artificial loblolly pine regeneration areas. Twenty-five habitat variables describing cover, forage, and structure were measured or derived at each trap station. We used discriminant function analysis (DFA) to construct microhabitat utilization models for the six most abundant small mammal species common to young loblolly pine regeneration areas including the southern short-tailed shrew ( Blarina carolinensis ), golden mouse ( Ochrotomys nuttalli ), white-footed mouse ( Peromyscus leucopus ), cotton mouse ( P. gossypinus ), harvest mouse ( Reithrodontomys humulis ), and cotton rat ( Sigmodon hispidus ). We compared vegetation characteristics at stations where each species was captured versus stations where it was not captured. Models of species microhabitat associations helped explain observed differences in species succession and abundance. Coarse woody debris (i.e. logs and stumps) was found to be an important microhabitat component for O. nuttalli . Logs and stumps were important to P. gossypinus , P. leucopus and S. hispidus . Shrew capture stations had a significantly taller canopy and significantly greater biomass of vines than did non-shrew captures sites. Golden mouse capture stations had significantly longer logs, shorter distance to nearest log, and lower herbaceous profile diversity. Distance to nearest tree was significantly greater while tree height and vine cover were significantly lower at white-footed mouse capture stations. Cotton mouse microhabitat variables describing woody biomass were greater and stump size, tree height and distance to logs were significantly lower at capture stations. Harvest mice capture stations were characterized as having significantly lower tree height than non-capture stations. Cotton rat microhabitat was characterized by twelve variables but cotton rats were collected almost exclusively on the youngest stands with the greatest grass and herbaceous structure. Numerous variables play an important role in determining habitat quality for the array of small mammal species commonly found in early successional pine habitats in the southeast. Microhabitat models help to explain some of the patterns of species occurrence and succession. While the methods used in this study do not necessarily demonstrate preferred habitat, our results allow identification of areas of use.

To assess genic differentiation and phylogenetic relationships among selected species in the subgenus Aporodon, we screened 31 presumptive genetic loci in 6 species in the subgenus Aporodon (R. creper, R. gracilis, R. mexicanus, R. microdon, R. spectabilis, and R. tenuirostris) and in 4 species in the subgenus Reithrodontomys (R. chrysopsis, R. fulvescens, R. megalotis, and R. sumichrasti). The resulting phylogenetic trees were compared with the results of previous molecular and morphological studies. Results demonstrate that the subgenus Aporodon is monophyletic. Relationships determined on the basis of allozymes are largely congruent with an earlier analysis based on morphological and molecular characters. However, samples of R. mexicanus do not form a monophyletic lineage. Accordingly, populations from north-central Oaxaca and Costa Rica each likely represent an undescribed species.

Reithrodontomys spectabilis is an endemic rodent inhabiting Cozumel island in the Mexican Caribbean. This species is categorized as Threatened by Mexican law and as Critically Endangered by the IUCN. We report 10 polymorphic microsatellite loci, which were tested in 30 individuals trapped on the island. Results show a number of alleles ranging from 3 to 14, an observed heterozygosity of 0.200–0.967 and expected heterozygosities from 0.396 to 0.899. Two loci showed deviation from Hardy–Weinberg equilibrium. None of the loci showed linkage disequilibrium. These new microsatellite loci for R. spectabilis are vital to investigate different aspects of genetic diversity and help conservation of this endemic, threatened species.

Reportamos información descriptiva de las vocalizaciones de dos especies de ratones, analizando y describiendo sus variables espectrales y temporales. Reithrodontomys soderstromi presenta vocalizaciones similares a un silbido de frecuencia constante con una frecuencia dominante promedio de 10.16 ± 0.20 kHz; mientras que Thomasomys paramorum vocaliza como un chasquido de frecuencia modulada con una frecuencia dominante promedio de 1.74 ± 0.10 kHz, generando un armónico cuya frecuencia promedio es de 3.64 ± 0.24 kHz.

Levels of sequence variation in mitochondrial cytochrome-b gene were examined to ascertain if this molecule can provide a reference point in making decisions concerning species-level distinctions. DNA-sequence data from 4 genera of rodents (Neotoma, Reithrodontomys, Peromyscus,and Sigmodon) and 7 genera of bats (Artibeus, Carollia, Chiroderma, Dermanura, Glossophaga, Rhinophylla,and Uroderma), including recognized sister species, were examined to develop hypotheses for evaluating levels of sequence variation. Several patterns associated with DNA-sequence variation emerged from this study. Specifically, genetic distance values ,2% were indicative of intraspecific variation; values between 2 and 11% had a high probability of being indicative of conspecific populations or valid species and merit additional study concerning specific status; and values .11% were indicative of specific recognition. It appears that genetic distance values may be useful for determination of species boundaries under the framework of the Genetic Species Concept.

Hantaviruses, family Bunyaviridae, are rodent-borne RNA viruses that can cause hantavirus pulmonary syndrome (HPS) in various regions of the Americas. A coevolutionary relationship exists between hantaviruses and their specific rodent reservoir hosts; the phylogeny of the viruses generally matches that of the rodents. There are several Peromyscus -borne hantaviruses, including Sin Nombre virus, the most common cause of HPS in North America. This report describes the genetic detection and characterization of a newly discovered Peromyscus boylii -borne virus, Limestone Canyon (LSC) virus, the most divergent member of the Peromyscus -borne hantaviruses to date. Analysis of a 1209-nucleotide region of the S segment of LSC virus showed it to be more closely related to hantaviruses found in harvest mice ( Reithrodontomys megalotis and R. mexicanus ) than to other Peromyscus -associated hantaviruses (Sin Nombre, New York, and Monongahela). Phylogenetic analysis of virtually the entire M genome segment (3489 nucleotides) of LSC virus revealed a similar picture in which LSC virus was found to be very distinct from other Peromyscus -associated viruses, but its exact relationship to the other Peromyscus -borne and the Reithrodontomys -borne viruses was not resolved. These results indicate that hantavirus host species-jumping events can occur by which a hantavirus may switch to, and become established in, a rodent host belonging to a different genus. P. boylii are present throughout the southwestern United States and central Mexico. More extensive screening of HPS patients by using RT–PCR assays will be necessary to determine if LSC virus can cause human disease.

Fecal samples from 54 Gunnison's prairie dogs (Cynomys gunnisoni) from Albuquerque, NM were analyzed for the presence of coccidia and all were positive. They were then relocated to an abandoned prairiedog town on the Sevilleta Long Term Ecological Research (LTER) site. Six Eimeria species, E. callospermophili, E. cynomysis, E. pseudospermophili (new host record), E. spermophili, E. ludoviciani and E. vilasi (new host record) were found in Albuquerque animals, but only 2 species, E. callospermophili and E. vilasi were present in relocated hosts. A significant (P < 0.05) reduction was seen in the prevalence of E. vilasi (72% vs. 13%) and in the prevalence of infections (P < 0.05) with 2 or more Eimeria species (39% vs. 4%) in pre- and postrelocation animals. To assess the impact of the introduction of C. gunnisoni on the resident rodent population, feces were collected from 6 species of rodents. Five Eimeria species, E. arizonensis (Reithrodontomys), E. chobotari (Dipodomys, Perognathus), E. liomys...

A new early Irvingtonian (latest Pliocene) rodent fauna is reported here from Inglis 1C, Citrus County, Florida. This sinkhole deposit near the west coast of the state contains 33 species of mammals, including 11 rodents, of which six are now extinct. A new species of Peromyscus, P. sarmocophinus , sp. nov., is described from this locality and the slightly older Inglis 1A. Inglis 1C contains the oldest records of three rodents ( Peromyscus polionotus, Reith- rodontomys humulis, and Atopomys texensis) and the youngest occurrences of two others (Reithrodontomys wetmorei and Ondatra idahoensis). Additionally, the paleogeographic range of two taxa, R. wetmorei and Baiomys sp., is extended east of the Mississippi River. Deposition at Inglis 1C was nearly contemporaneous with, the better-known, early Irvingtonian Inglis 1A fauna. The two localities share Sciurus sp., Glaucomys sp., Orthogeomys propinetis, Sigmodon curtisi, P. sarmocophinus, sp. nov., R. wetmorei and O. idahoensis. A slightly younger age at Inglis 1C is implied by the presence of P. polionotus, R. humulis, and Atopomys texensis. This fauna serves as an older complement to Florida's other well studied Irvingtonian localities, Leisey Shell Pits, Hillsborough County, and Coleman 2A, Sumter County.

Phylogenetic relationships among 7 species of Reithrodontomys were examined using the complete mitochondrial cytochrome-b gene. DNA-sequence data were analyzed using parsimony (weighted and unweighted) and genetic distance methods. In all analyses, R. sumichrasti, R. megalotis, and R. zacatecae formed a monophyletic clade. Likewise, R. montanus and R. raviventris were depicted as sister taxa in all analyses. Our study supports recognition of R. zacatecae as a species distinct from R. megalotis and recognition of R. raviventris as distinct from R. montanus. Patterns of chromosomal evolution were examined using differential staining as resolved by 3 DNA probes and fluorescent in situ hybridization. Using the phylogeny based on DNA sequences, we concluded that there has been extensive chromosomal repatterning (in most cases karyotypic megaevolution) in the evolution of R. zacatecae, R. megalotis, R. sumichrasti, R. montanus, R. raviventris, and R. humulis.

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.

This study reports results of a 14-month live-trap study of small-rodent communities in 2 habitats, cloud forest and disturbed areas, at Las Joyas Scientific Station of the Sierra de Manantlan Biosphere Reserve, western Mexico. Seven taxa of 2 families (Muridae, Heteromyidae) of small rodents were captured (Hodomys alleni, Liomys pictus, Oryzomys couesi, Peromyscus aztecus, Reithrodontomys fulvescens, R. sumichrasti, and Sigmodon alleni). Information about age structure, population dynamics, biomass, and reproduction were obtained with mark–recapture techniques for the most abundant species (P. aztecus and R. fulvescens) in both habitats. These species comprised 80.3% of the 707 captures in the cloud forest (P. aztecus, 51.2%; R. fulvescens, 29.1%), whereas, in the disturbed areas, R. fulvescens represented 81.7% of the 916 captures. Species varied in population density, relative abundance, and timing of reproduction, which was seasonal. Reproductive activity for P. aztecus peaked in the middle o...

Phylogenetic relationships among South American sigmodontine rodents were examined based on the complete sequence for the mitochondrial cytochrome b gene [1140 base pairs (bp)] for 66 species and between 759 and 1140 bp for an additional 19 species. Thirty-eight South American genera were represented, coming from eight of nine tribes. Outgroups included the North American murid rodents Peromyscus, Reithrodontomys, Scotinomys, and Neotoma, the Old World murine rodents Mus and Rattus, and the geomyoid genera Thomomys, Geomys, Dipodomys, and Perognathus as the most distant outgroup. The South American sigmodontines were supported as a monophyletic lineage. Within this radiation several clear-cut suprageneric groupings were identified. Many of the currently recognized tribal groupings of genera were found fairly consistently, although not always with high levels of bootstrap support. The various tribes could not be linked hierarchically with any confidence. In addition, several genera stand out as unique entities, without any apparent close relatives. The overall pattern suggests a rapid radiation of the sigmodontines in South America, followed by differentiation at the tribal and generic levels.

Population trends for seven genera of rodents were monitored by snap-trap capture rates on a study area (700 km2) in Webb County, Texas, during winter from 1976 to 1986. Population irruptions occurred in 1982 (46-fold) and 1986 (13-fold) for Sigmodon, and in 1982 (17-fold) for Reithrodontomys. Annual variability in abundance was positively correlated between the following pairs of genera: Sigmodon-Reithrodontomys, Peromyscus-Onychomys, Onychomys-Reithrodontomys, and Dipodomys-Chaetodipus. Annual abundance of Sigmodon in winter was positively correlated with rainfall in the prior growing season. Analysis of the distribution of the composite rodent community among five vegetative habitats revealed greater abundance of rodents in the most dense and diverse shrub community (high-density shrub/mixed-grass habitat).

A retrospective serosurvey for antibodies to Ehrlichia chaffeensis was conducted on eight species of wild rodents (Mus musculus, Oryzomys palustris, Peromysctts leucopns, Rattus norvegicus, Reithrodontomys humulis, Sciurus carolinensis, Sciurus niger, and Sigmodon hispidus) from the southeastern United States. Serum samples (n = 281) collected between 1973 and 1993 were evaluated using an indirect fluorescent antibody test. All samples, screened at a dilution of 1:32, were negative for antibodies to E. chaffeensis. Sixty-three percent of the rodents tested were from areas where E. chaffeensis has been confirmed or is strongly suspected to be endemic. These data suggest limited or no involvement of rodents in the epidemiology of E. chaffeensis.

Using fluorescence in situ hybridization, we examined the characteristics of two types of B chromosomes in harvest mice of the genus Reithrodontomys. B chromosomes were interrogated with rDNA, telomeric repeat, LINE element and centromeric heterochromatin probes. The two types of B chromosomes share the following features: (a) telomeres present on the ends of both arms; (b) hybridization to LINE probes; (c) absence of hybridization to the ribosomal gene probes; (d) C-band-positive centromeric regions; and (e) euchromatic arms. They differ as follows: (a) the larger B element hybridizes to the centromeric heterochromatin (pMeg-1) probe whereas the smaller B element does not; (b) the amount of C-band-positive material is reduced in the smaller B chromosome relative to that present on the larger B chromosome; and (c) the smaller element is reduced in size by about a third. It is concluded that the larger B chromosome arose as a leftover centromere from centric fusion, whereas the smaller element has a different origin — perhaps as an intact fragment or as an amplified region from the A chromosomes. The presence of euchromatic regions on B chromosomes may account for their survival in the karyotype.

Small mammal populations were characterized nine times during six sampling periods on six plots in five different fields of tall fescue (Festuca arundinacea Schreb.) to determine differences in their abundance and species composition associated with the presence or absence of the endophytic fungus Acremonium coenophialum Morgan-Jones & Gams. No differences were found in species richness (n=4 for both types) between endophyte-free (E - ) plots and endophyte-infested (E + ) plots. Capture success, number of individuals, total captures, and recapture rates were more for E - plots than for E + plots. All four species [eastern harvest mice (Reithrodontomys humulis Giglioli), short-tailed shrews (Blarina brevicauda Gray), pine voles (Microtus pinetorum McMurtrie), and cotton rats (Sigmodon hispidus Say & Ord)] were captured more often in E - than in E + plots. The diminished population densities of small mammals demonstrate the potential of E + tall fescue as a permanent ground cover for waste disposal sites, orchards, tree farms, irrigation ditch banks, golf courses, and other residential, commercial, and industrial situations where burrowing activities of mammals may create human hazards or financial burdens

We recently described a novel hantavirus (HMV-1) of the western harvest mouse Reithrodontomys megalotis. Screening of 181 additional specimens of Reithrodontomys from the United States and Mexico, including samples of R. mexicanus, R. sumichrasti, and R. gracilis of Costa Rica, for antibodies to hantavirus nucleocapsid protein revealed a widespread enzootic of hentavirus infection. Genetic analyses of 7 S genomes of Reithrodontomys -associated hantaviruses demonstrated that the enzootic of HMV-1 extends from central Mexico into the southwestern United States. A presumed deer mouse hantavirus was found in an R. megalotis animal in Mexico. A highly divergent HMV-1-like virus, tentatively called HMV-2, was identified in a Costa Rican R. mexicanus. These data suggest a longstanding radiation of hantaviruses among New World harvest mice. We identify possible opportunities for genetic exchange among hantaviruses of related rodent hosts.

This thesis contains 2 segments. The first segment concerns the annual and seasonal diets of the coyote (Canis latrans) on the Rolling Plains Quail Research Ranch. Northern bobwhite (Colinus virginianus) populations have been declining throughout the United States. Land use changes and habitat fragmentation are the primary reasons for bobwhite declines. However information is needed on interactions between coyotes and quail to make informed management decisions. This segment evaluates the diets of coyotes on a landscape managed intensively for quail between 2008 and 2011. The second segment concerns coyote preference and use of rodents on the Rolling Plains Quail Research Ranch. Little is known about the preference and selection of rodents by coyotes. This segment evaluates seasonal preference and selection of rodent genera during summer and winter between 2009 and 2011.

Se reportan ácaros ectoparásitos en roedores colectados durante un estudio ecológico en Playa de Oro, en el estado de Colima, México. Los roedores revisados fueron: Heteromys pictus, Heteromys spectabilis, Baiomys musculus, Nyctomys sumichrasti, Oryzomys couesi, Oryzomys melanotis, Osgoodomys banderanus, Reithrodontomys fulvescens y Sigmodon mascotensis. Se registra la presencia de varias especies de ácaros de las familias Laelapidae, Macronyssidae, Listrophoridae y Myocoptidae en nuevos huéspedes y de algunas más se amplía su distribución. Se registra por primera vez para México a Lepidoglyphus hylandi, Laelaps oryzomydis y Prolistrophorus bakeri.

An in situ investigation of structural chromosomal damage in wild rodents from a site contaminated with Aroclor 1254 was undertaken to compare effects observed in nature to those documented in previous laboratory studies. Laboratory assays indicate that Aroclor 1254 does not cause structural damage to chromosomes. However, the many variables at work in actual waste-site environments and receptor populations led us to question whether exposures under natural conditions could potentially lead to different results using the same assay systems. Individuals of three rodent species, Peromyscus leucopus, Sigmodon hispidus, and Reithrodontomys fulvescens, were collected from the contaminated site and three matched, pristine reference sites. Standard somatic metaphase chromosome preparations from bone marrow were examined for chromosomes lesions. Comparisons were made between conspecifics from the Aroclor-contaminated site and the reference sites. Significant increases in chromosome damage were not observed in animals from the Aroclor-contaminated site, indicating agreement between laboratory assays and an in situ application of this assay system.

In the United States, Bayou virus (BAYV) ranks second only to Sin Nombre virus (SNV) in terms of hantavirus pulmonary syndrome (HPS) incidents, having been confirmed in cases from Texas and Louisiana since its discovery in 1994. This study on BAYV infection among sympatric, non-oryzomyine rodents ("spillover") in Freeport, TX, is the first to link patterns of hantavirus interspecific spillover with the spatiotemporal ecology of the primary host (marsh rice rat, Oryzomys palustris). Mark-recapture and/or harvest methods were employed from March 2002 through May 2004 in two macrohabitat types. Rodent blood samples were screened for the presence of IgG antibody to BAYV antigen by IFA after which Ab-positive blood, saliva, and urine were analyzed for the presence of viral RNA by nested RT-PCR. From 727 non-oryzomyine captures, five seropositive (but not viral RNA positive) individuals were detected: one each of Baiomys taylori, Peromyscus leucopus, and Reithrodontomys fulvescens; and two Sigmodon hispidus. Spillover hosts were not associated with macrohabitat where O. palustris abundance, density, or seroprevalence was highest. Rather, spillover occurred in the macrohabitat indicative of greater overall disturbance (as indicated by grazing and exotic plant diversity) and overall biodiversity. Spillover occurred during periods of high seroprevalence detected elsewhere within the study region. Spillover locations differed significantly from all other capture locations in terms of percent water, shrub, and grass cover. Although greater habitat and mammal diversity of old-fields may serve to reduce seroprevalence levels by tempering intraspecific contacts between rice rats, greater diversity also may create an ecologically opportunistic setting for BAYV spillover. Impacts of varying levels of disturbance and biodiversity on transmission dynamics represent a vastly uncharacterized component of the evolutionary ecology of hantaviruses.

Reports of audible vocalizations are rare in adult muroid rodents, animals generally very small in body size and under strong predation pressure. By contrast, communication using high, often ultrasonic vocal frequencies is relatively common. There are anecdotal reports of audible vocalizations for some harvest mice (genus Reithrodontomys), however none have been recorded or analyzed. Several species of harvest mice are studied, representing the subgenera Reithrodontomys (R. fulvescens, R. sumichrasti) and Aporodon (R. creper, R. mexicanus, R. spp.), as part of a larger phylogenetic analysis of stereotypical vocal communication. Only R. mexicanus produced stereotyped vocalizations on a regular basis. Acoustic signals of R. mexicanus contain prominent harmonics bridging both the audible and ultrasonic range, with evidence of non-linear distribution of energy within and between notes of an individual call. Harmonic emphasis varies, making the carrier frequency difficult to locate. These Reithrodontomys vocalizations are compared with members of their phylogenetic sister group Onychomys+Peromyscus, genera whose stereotypic calls exclusively occupy the audible or ultrasonic spectrum, respectively. It is hypothesized that the stereotypic signals of harvest mice represent announcement calls. Given the number of anecdotal reports of stereotyped 1, 2, and 3-note calls among Reithrodontomys species, further interspecific comparisons are warranted.

Blood samples from 4893 cricetid rodents were tested for antibody (immunoglobulin G) to Whitewater Arroyo virus and Amapari virus to extend our knowledge of the natural host range and geographical distribution of Tacaribe serocomplex viruses in North America. Antibodies to arenaviruses were found in northern pygmy mice (Baiomys taylori), woodrats (Neotoma spp.), northern grasshopper mice (Onychomys leucogaster), oryzomys (Oryzomys spp.), deermice (Megadontomys nelsoni and Peromyscus spp.), harvest mice (Reithrodontomys spp.), and cotton rats (Sigmodon spp.) captured in New Mexico, Texas, or Mexico. Comparison of endpoint antibody titers to Whitewater Arroyo virus and Amapari virus in individual blood samples indicated that the Tacaribe complex viruses enzootic in Texas and Mexico are antigenically diverse.

International audience; Although Mexico's central arid and semiarid lands face numerous conservation problems, they have largely been neglected from conservation, despite their apparent biological importance. We studied the semiarid Llanos de Ojuelos, where the original plant communities of grasslands, shrublands, and patches of oaks have been modified strongly by cattle grazing and for cultivation, affecting animal populations and communities, as well as the landscape-level ecological dynamics. Very little about the populations of wild animals in the area and the processes underlying their distribution and dynamics is known. We focused on whether satellite information was useful to explain rodent distributions and abundances in this area with a complex landscape of diffuse plant communities. In the spring of 2008 we inventoried the rodents at 74 locations in the area, through the use of Sherman live-traps (40 traps during two nights, per site; total=5920 night-traps). We covered the major perennial vegetation types. The existence of a complex landscape of intergrading grasslands, Opuntia comunities and shrublands (dominated by Acacia, Mimosa, Dodonaea, and Quercus) of different types and composition creates rich habitat mosaic that promotes a rich rodent fauna. We captured 20 species of rodents (458 individuals), while richness was estimated at 21-25 species. Reithrodontomys fulvescens, Chaetodipus nelsoni, Dipodomys phillipsii, Peromyscus melanophrys, Peromyscus gratus, and Peromyscus difficilis were very common at our sites, while Chaetodipus pennicillatus, Liomys irroratus, Perognathus flavus, Dipodomys merriami, Reithrodontomys megalotis, Peromyscus boylii, Neotoma leucodon, Peromyscus eremicus, Dipodomys ordii, and Peromyscus manicultatus were common, and Neotoma goldmani, Chaetodipus hispidus, Onychomys arenarius, and Baiomys taylori were rare. To explore the value of satellite information to understand and predict the rodents' distributions, we derived reflectance data from all bands of a Landsat5 TM Image (5 March 2008) for each trapline's midpoint. We will compare each rodent species' abundance with this data as well as with the normalized difference vegetation index (NDVI) and tasseled cap transformations (TCs: brightness, greenness, and wetness). We will link rodent presence/absences to reflectance values through linear and non-linear discriminant analysis, as well as through general linear models and multiple adaptive regression splines. Satellite images classified following the best models will then be interpreted according to field expertise. As end results we expect to have a better understanding on the rodent species' ecology, an adequate image classification procedure, and potential distribution maps for the rodent species in the study area.

Small herbivorous mammals living in successional patchy environments may be affected by both patch size variations and successional changes. If patch size affects densities of residents then larger patches should have higher densities compared to smaller patches because larger patches often have greater habitat diversity and lesser chances of stochastic events destroying the population. If patch size affects length of time animals spend on patches (persistence rates) then smaller patches should have lower persistence rates compared to larger patches because smaller patches contain fewer resources. Larger animals may be constrained by body size, as well as population size, to reside only on the larger patches because smaller patches do not contain enough resources. If successional changes affect resident animals that are host specific on colonizing plant species, then the effects may be noticeable immediately following field abandonment because plant species replacement rates are most rapid then. Four small mammal species were included: Sigmodon hispidus, Reithrodontomys mega- lotis, Microtus ochrogaster, and Peromyscus maniculatus. The field was divided into patches that varied in area by two orders of magnitude with patches of each size treatment placed in each section of the field. Patch size effects on densities and persistence rates of the four mammal species were tested with analyses of variance. Plant species were grouped according to seven life history traits so as to include relative percent cover of most plant species. Multiple linear regression analyses were used to identify which variables (patch size, field sections, and percent relative cover) significantly explained variations in small mammal densities. Effects of patch size on animal densities and persistence rates varied among animal species. The largest species, Sigmodon hispidus, was never found on the smallest patches, but densities of Reithrodontomys megalotis, Microtus ochrogaster, and Peromyscus manicu- latus were often highest on the smallest patches. Animal density variations were often significantly explained by patch size using multiple regression analyses (P ? .001). However, lack of consistent trends with respect to the other independent variables included in the equations and variable R2 values suggested that other, unmeasured, variables may have influenced the results. Persistence rates of the three species were often highest on the largest patches. Results suggested that animals visited small patches more often than large patches without staying, and used large patches to create territories. Small and medium patches may have been used as archipelagos of preferred habitat interspersed with less desirable habitat. The first stage of old-field succession was completed by the end of the 3rd yr: perennials replaced annuals as the dominant plant species. Neither patch size nor field sections sig- nificantly affected percent cover.

Peromyscus melanotis is the only one of three mouse species that eats monarch butterflies at their overwintering sites in Mexico. I tested two hypotheses: 1)P. aztecus avoids monarchs because of a bitter taste aversion to cardiac glycosides (CGs) and an inability to reject CG-rich body parts; 2)Reithrodontomys sumichrasti avoids monarchs principally because of a bitter taste aversion to the CGs. None of the species are sensitive to the toxic effects of ingested CGs. Feeding responses of laboratory-reared mice of each species to monarchs with low, medium and high CG concentrations were compared. BothP. aztecus andR. sumichrasti ate significantly fewer of all three types of monarchs thanP. melanotis. ForP. aztecus andR. sumichrasti, the number of monarchs eaten decreased with increasing CG concentration, whereas forP. melanotis, the number remained constant.Peromyscus melanotis andR. sumichrasti developed a feeding technique for rejecting the CG-laden cuticular material, which reduced the bitterness of ingested monarch material. However,R. sumichrasti displayed the technique significantly less often thanP. melanotis; andP. aztecus never developed it. I conclude that high taste sensitivity to CGs and less versatile food handling preventP. aztecus andR. sumichrasti from overcoming the monarch's chemical defenses.

Three DNA probes isolated from three species of Reithrodontomys (R. montanus, R. megalotis, R. fulvescens) were used to examine within and among species variation in the chromosomal location of satellite DNA and constitutive heterochromatin. These probes hybridized to the centromeric regions on all chromosomes in six species of the subgenus Reithrodontomys. Additionally, nearly all extra-centromeric C-band positive regions (with the exception of some heterochromatic material on the X and Y) hybridized to these probes. Within the subgenus Reithrodontomys both the chromosomal distribution and organization of satellite DNA has changed throughout evolution. The evolutionary transition has been from a totally centromeric position in R. fulvescens to centromeric and non-centromeric regions in other species that have undergone extensive chromosomal rearrangements from the primitive karyotype for peromyscine rodents. In addition, the monomer repeat of the satellite sequence differs between R. fulvescens (monomer defined by PstI) and the remaining species in the subgenus Reithrodontomys (monomer defined by EcoRI). These results suggest at least two amplification events for this satellite DNA sequence. Models and mechanisms concerned with the homogenization and spread of satellite sequences in complex genomes are evaluated in light of the Reithrodontomys data. From a phylogenetic standpoint, the satellite sequences composing heterochromatic regions were restricted to the subgenus Reithrodontomys, which supports morphological differences used to recognize two subgenera, Reithrodontomys and Aporodon. Probes failed to hybridize to any part of the karyotype of R. mexicanus (subgenus Aporodon) or to seven species from other closely related genera (Baiomys, Neotoma, Nyctomys, Ochrotomys, Onychomys, Peromyscus, Xenomys), some of which are considered as potential sister taxa for Reithrodontomys.

Phylogenetic analyses for 10 rodent Eimeria species from different host genera based on plastid ORF470 and nuclear 18S rDNA sequences were done to infer the evolutionary relationships of these rodent Eimeria species and their correlation to morphology and host specificity. The phylogenies based on both data sets clearly grouped the 10 rodent Eimeria species into two major lineages, which reflect more their morphological differences than host specificity. Species in lineage A have spheroidal to subspheroidal sporulated oocysts, are similar in size (18-29 x 17-23; xbar = 22 x 20 microm), have an oocyst residuum and one-two polar granules; these include Eimeria albigulae (Neotoma), Eimeria arizonensis (Peromyscus, Reithrodontomys), Eimeria onychomysis (Onychomys) and Eimeria reedi (Perognathus). Species in lineage B, including Eimeria falciformis (Mus), Eimeria langebarteli (Reithrodontomys), Eimeria nieschulzi (Rattus), Eimeria papillata (Mus), Eimeria separata (Rattus) and Eimeria sevilletensis (Onychomys) have different shapes (ovoid, ellipsoid, elongated ellipsoid, etc.), differ greatly in size (10-27 x 9-24; xbar = 19 x 16 microm) and all lack an oocyst residuum. Thus, The oocyst residuum was the most determinant feature that differentiated the two lineages. The accession numbers of ORF470 of E. albigulae, E. arizonensis, E. falciformis, E. nieschulzi, E. onychomysis, E. papillata, E. reedi, E. separata, E. sevilletensis, E. langebarteli are AF311630-AF311639 and 18S rDNA of E. langebarteli, E. papillata, E. reedi, E. separata, E. sevilletensis are AF311640-AF311644.

A long-term monitoring program begun 1 year after the epidemic of hantavirus pulmonary syndrome in the U.S. Southwest tracked rodent density changes through time and among sites and related these changes to hanta–virus infection rates in various small-mammal reservoir species and human disease outbreaks. We assessed the statistical sensitivity of the program's field design and tested for potential biases in population estimates due to unintended deaths of rodents. Analyzing data from two sites in New Mexico from 1994 to 1998, we found that for many species of Peromyscus, Reithrodontomys, Neotoma, Dipodomys, and Perognathus, the monitoring program detected species-specific spatial and temporal differences in rodent densities; trap-related deaths did not significantly affect long-term population estimates. The program also detected a short-term increase in rodent densities in the winter of 1997-98, demonstrating its usefulness in identifying conditions conducive to increased risk for human disease.

The frequency and distribution of chiasma in meiotic of four species of Reithrodontomys (fulvescens, humulis, megalotis and montanus) were examined using standard light microscopy. R. fulvescens and R. humulis have the highest Rl values and R. megalotis and R. montanus have the lowest. Among these species, the reduction in the number of linkage groups appears to indicate an increase in specialization. In all species examined in this study, a non-random distribution of chiasma was found. Four individuals of R humulis had a n = 27 cytotype and two of these had the two smallest chromosome sets unpaired in all cells examined. In both individuals, an examination of prophase II cells indicated a normal chromosomal complement. The sex chromosomes of each species have an end-to-end association, however, the presence or absence of chiasma was not determined. The X chromosomes were heteropycnotic in each species with the short arms being stained more than the short arms. In R. megalotis, chiasma frequency did not differ significantly between cells whh and whhout supernumeraries. Cells that had more than one supernumerary contained less proximal chiasmata than those with one or none.

Determining and understanding evolutionary relationships of organisms is a goal in systematics. Initial studies of the genus Reithrodontomys addressed the subspecific affinities of species within the genus in portions of their ranges (Hooper 1952; Jones and Mursaloglu 1961). The focus of subsequent investigations has evolved beyond the taxonomic level of the subspecies, and has paralleled the development of new genetic and molecular techniques, such as standard karyotype analysis (Shellhammer 1967; Carleton and Myers 1979; Engstrom et al. 1981), G- and C- banding of chromosomes (Robbins and Baker 1980), starch-gel electrophoresis of allozymes (Arnold et al. 1983), and most recently, in situ hybridization of satellite DNA (Hamilton et al. 1990). Thus, many of the questions regarding Reithrodontomys pertain to phylogenetic relationships. Despite the many studies of Reithrodontomys, important questions relative to variation among populations of species within the genus remain unanswered. Reithrodontomys megatotis, from the Southern High Plains in West Texas, represents a taxon in which variation within and among populations is not well understood. This species Is a relatively rare or elusive inhabitant of the area, and to date, these characteristics have prevented a thorough study of populational differences in this geographical region. Currently, two subspecies (R m. aztecus, R. m. megatotis), are recognized rom this expanse in West Texas. The purpose of this study is to examine specimens from this region, and through the use of phenetic techniques and statistical analyses, elucidate the extent of nongeographic and geographic variation in R. megatotis, and assess the subspecific status of R. megatotis on the Southern High Plains.