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Suisun Marsh (Solano County, California) is the largest contiguous marsh remaining on the West Coast of the United States, and makes up approximately 10% of the wetlands remaining in the San Francisco Estuary. Suisun Marsh has been safeguarded from development through the operation of over 100 privately owned waterfowl hunting clubs, which manage for diked waterfowl habitat. However, this management-and the subsequent loss of tidal influence-has been considered harmful for some species, including the endangered salt marsh harvest mouse (SMHM; Reithrodontomys raviventris). To determine the value of tidal wetlands relative to those managed for waterfowl, we performed periodic surveys for rodents in managed and tidal wetlands over 5 years, and used capture-mark-recapture analyses to estimate demographic parameters and abundance for the three most common rodents-the northern SMHM (R. r. halicoetes), the western harvest mouse (a sympatric native species; R. megalotis, WHM), and the house mouse (a sympatric invasive species; Mus musculus). Wetland type had no effect on detection, temporary emigration, or survival for any of these species. However, fecundity and population growth for all three species were affected by an interaction of season and wetland type, although none of these parameters was consistently superior in either habitat type. Estimated abundance of SMHM and Mus was similar in both wetland types, whereas WHM were more abundant in managed wetlands. Salt marsh harvest mice also showed no affinity for any microhabitat characteristics associated with tidal wetlands. Managed wetlands in Suisun Marsh support SMHM and Mus equally, and abundances of WHM were greater than in tidal wetlands, suggesting managed wetlands may be superior in terms of supporting native rodents. As climate change and sea level rise are predicted to threaten coastal marshes, these results suggest the recovery strategy for SMHM could incorporate managed wetlands.

Context: Vector-borne diseases have caused global pandemics and were responsible for more human deaths than all other causes combined in prior centuries. In the past 60 years, prevention and control programs have helped reduce human mortality from vector-borne diseases, but impacts of those control programs on wildlife populations are not well documented. Insecticides are used to reduce vector-borne diseases in several critically endangered animal populations. Although insecticides are often effective at controlling targeted vectors, their effects on non-target species have rarely been examined. Aims: To evaluate the impact of deltamethrin (an insecticide) on sympatric non-target species in areas affected by sylvatic plague, a lethal flea-borne zoonosis. Methods: We compared flea control and the effect of deltamethrin application on survival of non-target small mammals (Peromyscus maniculatus , Chaetodipus hispidus , Microtus spp., and Reithrodontomys megalotis) at three study locations in South Dakota, Colorado, and Idaho, USA. Key results: Deltamethrin treatments were more effective in reducing fleas on P. maniculatus and Microtus spp. than C. hispidus. Following burrow, nest, and bait-station applications of deltamethrin dust, apparent small mammal survival was greater for non-treatment animals than for flea-reduction animals. However, the magnitude of the difference between treated and non-treated animals differed among host species, study location, time interval, and treatment application method. Conclusions: Our results suggest that considering the impact of deltamethrin on co-occurring non-target species before widespread application in future insecticide applications is warranted. Implications: Insecticide application methods warrant consideration when designing plague management actions. Insecticides are applied worldwide as a tool to control both wildlife and/or human diseases but we need to document the impact these chemicals have on non-target animals. We examined and discovered that deltamethrin (an insecticide used to control flea vectors of the plague bacterium) reduced survival of non-target small animals in three different study sites in the western United States. Insecticides are an important tool to conserve species threated by wildlife diseases, but we need to consider and evaluate their effects on non-target animals when making management decisions regarding the best methods to reduce disease prevalence. Photograph by Amanda R. Goldberg. [ABSTRACT FROM AUTHOR]

Suisun Marsh (Solano County, California) is the largest contiguous marsh remaining on the West Coast of the United States, and makes up approximately 10% of the wetlands remaining in the San Francisco Estuary. Suisun Marsh has been safeguarded from development through the operation of over 100 privately owned waterfowl hunting clubs, which manage for diked waterfowl habitat. However, this management—and the subsequent loss of tidal influence—has been considered harmful for some species, including the endangered salt marsh harvest mouse (SMHM; Reithrodontomys raviventris). To determine the value of tidal wetlands relative to those managed for waterfowl, we performed periodic surveys for rodents in managed and tidal wetlands over 5 years, and used capture-mark-recapture analyses to estimate demographic parameters and abundance for the three most common rodents—the northern SMHM (R. r. halicoetes), the western harvest mouse (a sympatric native species; R. megalotis, WHM), and the house mouse (a sympatric invasive species; Mus musculus). Wetland type had no effect on detection, temporary emigration, or survival for any of these species. However, fecundity and population growth for all three species were affected by an interaction of season and wetland type, although none of these parameters was consistently superior in either habitat type. Estimated abundance of SMHM and Mus was similar in both wetland types, whereas WHM were more abundant in managed wetlands. Salt marsh harvest mice also showed no affinity for any microhabitat characteristics associated with tidal wetlands. Managed wetlands in Suisun Marsh support SMHM and Mus equally, and abundances of WHM were greater than in tidal wetlands, suggesting managed wetlands may be superior in terms of supporting native rodents. As climate change and sea level rise are predicted to threaten coastal marshes, these results suggest the recovery strategy for SMHM could incorporate managed wetlands. [ABSTRACT FROM AUTHOR]

The Eastern Harvest Mouse, Reithrodontomys humulis, has been studied extensively in southeastern Virginia since 1979, using a combination of live and pitfall trapping methods. This smallest rodent of eastern North America also is one of most versatile, occupying a range of habitats in southeastern Virginia from old fields in different stages of succession, brushy edges, and forests of different types. As with other species of Reithrodontomys, R. humulis often is associated with the Hispid Cotton Rat, Sigmodon hispidus, with both reaching modest densities in old fields. Two capture-mark-release studies of small mammal communities in southern Chesapeake lasting eight and nine years revealed that the Eastern Harvest Mouse was third in total abundance, behind Hispid Cotton Rat and Meadow Vole, Microtus pennsylvanicus, as old fields transitioned into forests. Multiple field studies using pitfall traps in a range of habitats in southeastern Virginia also indicated that harvest mice often arrive early in succession and stay later than other rodents. [ABSTRACT FROM AUTHOR]

Studying animal space use patterns can help increase our understating of ecological processes such as competition and community dynamics. To quantify space and habitat use in an isolated and patchy cloud forest community in Mexico, we evaluate the vertical stratification, home range and habitat selection of two arboreal rodents: Habromys schmidlyi and Reithrodontomys microdon. Using live-traps at ground level and different forest strata, we radio-equipped nine individuals of H. schmidlyi and seven of R. microdon, and evaluated fine-scale space use and broad-scale habitat selection between cloud forest and oak forest. We found an average home range of 0.24 ha for R. microdon males and 0.72 ha for females, with a preference for higher canopy in the cloud forest. For H. schmidlyi the home range was 0.83 ha for males and 0.29 ha for females, with a preference for the understory level in the cloud forest. Home range is three-dimensional for these rodents, so we estimate that on average, individuals of both species used eight trees in the time they were tracked. We characterised the vegetation at the trap sites, and used recursive partitioning to relate the presence of different plants with the probability of finding these two species and Peromyscus aztecus, a third rodent species also present in the area and considered in our analysis of habitat use. The highest probability of finding R. microdon (96%) was related to the presence of Brachythecium occidentale and Renauldia mexicana, while H. schmidlyi (95%) was found in close proximity to Fabronia ciliaris and Everniastrum. We highlight the importance of arboreal trapping in biodiversity assessments, and the role of arboreal rodents in maintaining tropical forest ecosystems. We suggest that these rodent species could avoid or reduce competition by using the vertical strata differentially, and that H. schmidlyi and R. microdon can be biological indicators for cloud forest management and conservation. [ABSTRACT FROM AUTHOR]

Copemyodon ecuadorensis was described as a non-sigmodontine extinct cricetid from two rich fossiliferous localities in northern Ecuador. It was hypothesized as being related to both the fossil genus Copemys and the living Peromyscus and, as such, is an example of an independent "copemyine-neotomine" attempt to colonize South America. Here, we re-study the holotype of C. ecuadorensis concluding that it cannot be separated from Reithrodontomys (Cricetidae, Neotominae) at a generic level. Copemyodon constitutes a junior synonym of Reithrodontomys. There are recent populations of Reithrodontomys in Ecuador and most likely it comprises several species. In this context, seems convenient to retain ecuadorensis as a species of Reithrodontomys until an appropriate revision of this genus is performed, although we identify morphological similarities between Reithrodontomys ecuadorensis and the nominal form Reithrodontomys soederstroemi. [ABSTRACT FROM AUTHOR]

The introduced black rat, Rattus rattus, occurs throughout the native range of the raccoon roundworm, Baylisascaris procyonis, and might incorporate into its life cycle if rats consume parasite eggs, acquire viable infections, and are eaten by raccoons. Although rats forage at raccoon latrines, their role in B. procyonis transmission remains unknown. Here I tested the potential for rats to amplify B. procyonis transmission in California by surveying wild rodents for B. procyonis and conducting scavenger trials with the use of motion-activated cameras. Rattus rattus were infected with B. procyonis at intensities more than 100 times greater than that of co-occurring native Reithrodontomys megalotis and Peromyscus maniculatus. Rodent carcasses were scavenged by opossums, skunks, and raccoons, suggesting that these rodents, particularly R. rattus, contribute to B. procyonis transmission in this coastal California ecosystem. [ABSTRACT FROM AUTHOR]

Following decades of fire suppression many oak-pine savanna ecosystems have shifted to closed-canopied forests. Restoration of these ecosystems to their savanna condition is seen as a way to reduce woody species encroachment and dangerous fuel loads, and restore community species composition. The management practices to achieve these goals typically involve thinning and prescribed fire. We assessed how thinning to reduce basal area combined with frequent prescribed fire influenced small mammal communities and their habitat. We focused on six habitat variables that can influence small mammal abundance and species composition: stand basal area of live trees and snags, volume of coarse woody debris, percent ground cover, forest floor depth, and distance of vulnerability, a measure of understory vegetation structure and animal vulnerability to predators. Although savanna restoration reduced basal area by 80%, there was no change in snag density or coarse woody debris volume. Savanna restoration significantly increased the ground cover of graminoids, forbs, bare ground, and down woody debris and reduced forest floor depth and distance of vulnerability. These habitat changes likely contributed to the significant differences between small mammal communities in restored and non-restored stands. Restoration treatments caused a large increase in abundance of White-footed Mouse ( Peromyscus leucopus ) and important changes in community assemblages. Least Shrew ( Cryptotis parva ), Fulvous Harvest Mouse ( Reithrodontomys fulvescens ), Eastern Harvest Mouse ( R. humulis ), and Hispid Cotton Rat ( Sigmodon hispidus ) were caught only in restored stands, while House Mouse ( Mus musculus ), Plains Harvest Mouse ( R. montanus ) , and Texas Mouse ( P. attwateri ) were caught only in non-restored stands. [ABSTRACT FROM AUTHOR]

The salt marsh harvest mouse (SMHM, Reithrodontomys raviventris) is an endangered species endemic to the San Francisco Bay region of California, USA, where habitat loss and fragmentation over the past century have reduced the mouse's distribution to <25 % of its historical range. To aid in conservation prioritization, we first investigated the possibility of hybridization with the morphologically similar western harvest mouse (WHM, R. megalotis) in areas of sympatry and developed genetic tools to differentiate the two species. We then investigated the phylogeography and genetic structure of the SMHM, including support for currently recognized SMHM subspecies designations. Lastly, we evaluated the morphological criteria currently used for the identification of species in the field. Analyses using mtDNA cytochrome b sequences and 11 microsatellites from 142 mice indicated complete and substantial separation of the SMHM and WHM, with no evidence of hybridization. These genetic markers as well as the mtDNA control region also identified a deep genetic division within the SMHM concordant with the current subspecies designations, R. r. raviventris and R. r. halicoetes. We identified the lowest genetic diversity within the southern subspecies, which inhabits a much reduced and highly fragmented portion of the species range. Morphological field identification of harvest mouse species was more successful at identifying SMHM (92 %) than WHM (44 %), with a large portion of WHM being incorrectly identified as SMHM. Field identification of harvest mouse species in the range of the southern SMHM subspecies was just above 50 %, indicating that current methods for morphological differentiation of species in that area are insufficient. Our confirmation of genetically distinct SMHM subspecies highlights the importance of determining the status and genetic composition of relict populations in the remaining patches of marshland in the central San Francisco Bay where the two subspecies may occur, as well as developing better tools for the discrimination of species, particularly in the range of the southern subspecies [ABSTRACT FROM AUTHOR]

The species of harvest mouse Reithrodontomys megalotis belongs to one of the most diverse genera in North America with a wide latitudinal and altitudinal distribution. Previous studies suggest the existence of great morphological, chromosomal, and genetic variability; however, few of them have addressed the evolutionary patterns at the intraspecific level. We analyzed the evolutionary relationships and levels of genetic divergence in R. megalotis using DNA sequences of the mitochondrial cytochrome b gene. The results of the analysis with different phylogeographic methods show that R. megalotis represents a monophyletic group with respect to R. zacatecae, and populations included here split in three groups that were always consistent. Populations from the southern distribution form the first clade; from western North America form the second clade; and the third one comprises the populations of the Central Plains from the southern United States and the Mexican Plateau. The values of average genetic divergence within and among clades are low (< 3.4 %) compared to other species with similar distribution and times of divergence and origin. The results of this work are discussed in the context of the low genetic divergence found, given its wide and heterogeneous distribution together with its morphological variation. It is suggested that populations of R. megalotis have probably developed considerable phenotypic plasticity whose analysis and description should be approached from an ecological more than historical perspective. [ABSTRACT FROM AUTHOR]

Reithrodontomys megalotis and R. montanus, two species of harvest mouse that co-occur at low elevations of the southeastern Rockies and western Great Plains, are notoriously difficult to distinguish both externally and cranially, particularly for juveniles. Three external characteristics and 14 cranial measurements were used in discriminate function analyses (DFA) to detect the most robust measurements for species identification. Using 151 and 66 specimens of R. megalotis and R. montanus, respectively, from Colorado, we constructed DFA models for all specimens combined and segregated into four age classes by tooth wear. Due to substantial overlap in measurements, DFA models could not reliably predict species identity based on external or cranial characteristics alone, whereas models including all characteristics were more reliable. The most reliable DFA models were those for each age class (juvenile, subadult, adult, and old adult) using all external and cranial measurements. With various DFA models, 19 juvenile and subadult specimens of Reithrodontomys sp. from recent trapping efforts were all classified as R. megalotis with an average probability of 99.7%. Tail stripe width was also shown to be an unreliable identifier. We advocate using combined external and cranial measurements segregated by age class to robustly discriminate between these two species, particularly when identifying young individuals. [ABSTRACT FROM AUTHOR]

We assessed the genetic structure and diversity of Reithrodontomys spectabilis, a critically endangered, endemic rodent from Cozumel Island, México. A total of 90 individuals were trapped from September 2001 to January 2005. Microsatellite data analysis revealed high genetic diversity values: a total of 113 alleles (average 12.5 per locus), H = 0.78, H = 0.80. These high values can be related to Cozumel's size (478 km) and extensive native vegetation cover, factors that could be promoting a suitable population size, high heterozygosity and the persistence of rare alleles in the species, as well as some long-term movement of individuals between sampling localities. A strong genetic structure was also observed, with at least four genetic groups, associated with a pattern of isolation by distance. We found a strong allelic and genetic differentiation shown between localities, with negligible recent gene flow and low inbreeding coefficients. The species life history and ecological characteristics-being nocturnal, semi-terrestrial, a good tree climber, having lunar phobia and significant edge effect-are likely affecting its genetic structure and differentiation. The high genetic diversity and population structure award R. spectabilis a significant conservation value. Our results can serve as a basis for future research and conservation of the species, particularly considering the problems the island is facing from habitat perturbation, urbanization and introduction of exotic species. In view of the structure and genetic variability observed, it is essential to establish and reinforce protected areas and management programs for the conservation of the endemic and endangered Cozumel Harvest mice. [ABSTRACT FROM AUTHOR]

Abstract: A variety of hantaviruses are harbored by rodents in North and South America, some of which can cause hantavirus pulmonary syndrome. To obtain greater evolutionary insight into hantaviruses in the Americas, a total of 211 rodents were captured in the Mexican states of Guerrero and Morelos in 2006. Anti-hantavirus antibodies were detected in 27 of 211 serum samples (12.8%) by ELISA. The distribution of seropositive rodents was: 17 Peromyscus beatae, 1 Megadontomys thomasi, 1 Neotoma picta, 6 Reithrodontomys sumichrasti, and 2 Reithrodontomys megalotis. The hantavirus small (S), medium (M), and large (L) genome segments from P. beatae, R. sumichrasti, and R. megalotis were amplified and the sequences covering the open reading frames were determined. The hantaviruses from P. beatae, R. sumichrasti, and R. megalotis were provisionally designated Montano (MTN), Carrizal (CAR), and Huitzilac (HUI), respectively. The M segment amino acid identities among the Mexican hantaviruses were 80.8–93.0%. When these M segments were compared to those of known hantaviruses, MTN virus was most closely related to Limestone Canyon (LSC) virus (88.9% amino acid identity), while the CAR and HUI viruses were most closely related to El Moro Canyon (ELMC) virus (90–91% identity). Phylogenetic analysis revealed that the MTN, CAR, and HUI viruses occupy a monophyletic clade with the LSC, ELMC, and Rio Segundo viruses, which are harbored by Peromyscus boylii, R. megalotis, and Reithrodontomys mexicanus, respectively. The data obtained in this study provide important information for understanding the evolution of hantaviruses in the Americas. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

We conducted a formal survey of small-mammal ectoparasite diversity in Iowa. We examined 166 small mammals and documented 54 species of parasitic arthropods present on 12 species of mammals. Ectoparasite species richness was greatest for Blarina brevicauda (northern short-tailed shrew), Microtus ochrogaster (prairie vole), Peromyscus maniculatus (deer mouse), and Peromyscus leucopus (white-tooted mouse). Immature (larvae and nymphs) Dermacentor variabilis (American dog tick) were collected from P. leucopus, M. ochrogaster, Reithrodontomys megalotis (western harvest mouse), and Zapus hudsonius (meadow jumping mouse). The fleas Epitedia wenmanni and Orchopeas leucopus, potential vectors of sylvatic plague bacilli, were found on Mus musculus (house mouse), white-footed mouse, and deer mouse. We document 21 new ectoparasite host records for North America and 115 new host locality records for ectoparasites in Iowa. [ABSTRACT FROM AUTHOR]

1. Density dependence has an important influence on the dynamics of many species of small mammals. To regulate population growth, density must affect negatively a vital rate (e.g. fecundity); however, little is known about which vital rates are most affected by density. 2. We used a long-term data set for five species of rodents from north-eastern Kansas, USA to test for relationships between density and the proportion of pregnant females, per capita fecundity and recruitment. We estimated proportion of pregnant females using data collected in the field and fecundity using data on survival, proportion of pregnant females and literature-based density-dependent litter size for each species. We used reverse capture histories to estimate per-capita recruitment. 3. The proportion of pregnant females was related positively to density in most species. Fecundity was related negatively to density in the cotton rat ( Sigmodon hispidus Say & Ord, 1825) and not related to density in the four remaining species. Recruitment was related negatively to density in all five species, although not all relationships were statistically significant. 4. The signature of density-dependent recruitment was strongest in the prairie vole [ Microtus ochrogaster (Wagner, 1842)] and cotton rat and less so in the remaining species. 5. Our analyses indicate that density affects recruitment negatively in grassland small mammals either through a reduction in immigration or reduced survival of nestlings. Models that seek to include empirical estimates of density dependence may need to include immigration in addition to survival and fecundity. [ABSTRACT FROM AUTHOR]

Population ecology of the mouse Peromyscus mexicanus (Rodentia: Muridae) in Poas Volcano National Park, Costa Rica. The Mexican Deer Mouse has been reported as an abundant wild mouse in Costa Rica; nevertheless, it has not been studied as well as other Peromyscus species. Thirty Sherman traps were placed on three habitats during six consecutive days of each month, from March 2002 through April 2003 in three sites of Poás volcano National Park, Costa Rica. A total of 2 393 mice were captured. Other species such as Reithrodontomys creper, R. rodriguezi, Scotinomys teguina and Oryzomys devius (Muridae) were also captured in Tierra Fría and R. creper, R. sumichrasti, S. teguina and O. devius in Potrero Grande. in Canto de las Aves we captured P. mexicanus, R. creper, R. rodriguezi and O. devius. Of the total mice collected, 34.77 % were P. mexicanus. For this species, the mean monthly capture per hectare was 34 ± 2.15 in Tierra Fría and 11 ± 1.85 in Potrero Grande. in the third site, Canto de las Aves, only four mice were captured throughout the study. The estimated population size did not change among months in Tierra Fría, but it did in Potrero Grande. No sex ratio variation was found in any habitat. in Potrero Grande, weight averages were 43.54 ± 3.42 g for males and 42.08 ± 3.4 5 g for females. variation in population structure among habitats was not significant. The presence of oak trees (Quercus sp.) and the high under-story density could explain the stability of the population in this area. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 identified 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 finding 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 significantly 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 identified 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. [Copyright &y& Elsevier]

We conducted a mark-recapture experiment to examine population dynamics of the fulvous harvest mouse (Reithrodontomys fulvesrcens) 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 probabilides 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 plots during winter 1999-2000. As low-level nitrogen amendments continue to be applied, we predict survival and densities of R. montanus and R. fulvescens on control plots, especially fenced plots with no nitrogen amendment, will eventually exceed those on nitrogen-amended plots as a result of higher plant species diversity, food availability and better quality cover. [ABSTRACT FROM AUTHOR]

This article focuses on the spatial clustering of disease occurrence or pathogen transmission. Recent examples include bluetongue viruses and contagious bovine pleuropneumonia in livestock, leptospirosis and rabies among dogs, Lassa virus in small mammals, and rat bites and visceral leishmaniasis in humans. Therefore, the use of space by hosts of pathogens is an important principle in the epidemiology of many infectious diseases, at both the regional and local levels. The apparent spatial clustering of rodents infected with a hantavirus has been observed in several previous studies. Ecologists have attempted to address this issue in a quantitative manner at the local level. New tools, including spatial statistics methods, enable researchers to address the spatial aspects of diseases more thoroughly and less subjectively' than simple descriptions. Meta-analysis, the statistical synthesis of research results from a set of primary studies, has recently been introduced to ecology. Their objective was to determine quantitatively, the difference in the general space use/clustering of hantavirus-infected and uninfected murid rodents of the same species.

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. [ABSTRACT FROM AUTHOR]

Examines phylogenetic relationships among several species of Reithrodontomys using the complete mitochondrial cytochrome-b gene. Result of fluorescent in situ hybridization experiment; Tamura-Nei genetic distances for Reithrodontomys species examined; Discussion of karyotypic megaevolution.

Based on the first record in the state of Morelos and a new record for the Estado de México, we suggest that Reithrodontomys microdon preferentially uses an arboreal habitat. Specimens described here, for the most part (75%), were captured >4 m above ground on trees. Although historical records indicate that R. microdon is rare, our data may suggest otherwise. Assuming this species is preferably arboreal and that most inventories of rodents have focused on the ground, it is evident that, historically, this species has not been surveyed in its preferred habitat. [ABSTRACT FROM AUTHOR]