Small Rodent Species Research Articles

The Rodent Trade of Tzeltal Indians of Oxchuc, Chiapas, Mexico

Wildlife has always been an important natural resource for human societies to satisfy their need for food, clothing, medicine, tools, fuel, and ritual objects (Fa et al. 2002; P?rez-Gil et al. 1995). In particular, wild mammals have been a major source of protein for rural societies throughout Latin America (Ojasti and Dallmeier 2000; Redford and Robinson 1987; Robinson and Redford 1991). In Mexico alone, around 100 wild mammal species have known uses by local communities (Lopez-Wilchis et al 1992; Naranjo et al. 2004; Uribe and Arita 1998). In spite of the fact that small rodent species represent a significant part of mammalian diversity (Ceballos et al. 2002), the recorded use of rodents in Mexico has focused on large and medium-sized species (Guerra 2001; Jorgenson 2000; Naranjo 2002). However, there is evidence of the use of small rodents as sources of

Effects of diet quality on phenotypic flexibility of organ size and digestive function in Mongolian gerbils (Meriones unguiculatus)

In the context of evolution and ecology, there is a trade-off between the benefits of processing food through a digestive system with specific phenotypic attributes and the cost of maintaining and carrying the digestive system. In this study, we tested the hypothesis that digestive modulations at several levels can match each other to meet the energy and nutrient demands of Mongolian gerbils, a small granivorous rodent species, by acclimating them to a high-quality diet diluted with alfalfa powder. Mongolian gerbils on the diluted diet maintained metabolizable energy intake by an integrated processing response (IPR), which included increases in dry matter intake, gut capacity and rate of digesta passage after 2-weeks of acclimation. Down-regulation of hydrolytic enzyme activity in the intestinal brush-border membrane supported the adaptive modulation hypothesis. The absence of up-modulation of summed enzyme hydrolytic capacity on the diluted diet indicated that greater mass of small intestine on a high-fibre diet is not a direct indicator of digestive or absorptive capacity. Changes in mass of vital organs and carcass suggested that the amount of energy allocated to various organs and hence physiological functions was regulated in response to diet shift.

Comunidad de pequeños roedores en una milpa tradicional del centro de Yucatán, México.

Abstract. A small rodent species was studied in two agroecosystems from Yucatan: (1) a traditional cornfield and (2) an induced grassland. A total of 87 individuals of six species in two families (Heteromyidae y Cricetidae) were captured rendering an effort of 2,544 nights/trap. Heteromys gaumeri and Peromyscus yucatanicus were the most abundant species with 57.5% and 17.2% of total captures, respectively. Highest captures were recorded in the traditional cornfield and the highest species richness was obtained in the grassland. No significant differences in diversity were found between sites (p > 0.05). It seems that the cornfield plays an important role on both the diversity and population dynamics of small rodents because it presents the highest values in captures, density, recruitment, and in reproductive individuals. This may be related to a greater variety of cultivated plant species in this agroecosystem. Key words: Small mammals, rodents, Cornfield, Grassland, Yucatan, Mexico. Palabras clave: Pequeños mamíferos, roedores, milpa, pastizal, Yucatán, México.

‘‘Vocal grooming’’ in an eusocial subterranean rodent: The naked mole-rat (Heterocephalus glaber)

The naked mole-rat is a unique communal-living rodent of east Africa. In a subterranean environment, this small rodent species has a complex hierarchical society with labor division that is comparable to those of bees and ants. They are also known for their extensive vocal repertory of more than 17 sounds, which might have evolved as an alternative to visual cues, and which contributes to maintaining its society. We showed that their most frequent vocalization, the soft-chirp (SC), has an antiphonal nature, and it might function for rank-identification and reconciliation purposes. The SC is elicited either by another’s SC or physical touch. We analyzed acoustic properties of SC elicited by touching the animals, and found that it varies according to the body mass. The emission rate was highest among larger (superior) animals, but the smaller (inferior) of the two emitted SCs more frequently when observing behavior of two interacting animals. Playback experiments revealed that the use of SC generally follows these two rules: smaller animals vocalize more often than larger ones, and larger ones respond only to smaller animals’ SCs. These features of SC resemble grooming behavior among primates.

Comparison of diets of the acouchy, agouti and paca, the three largest terrestrial rodents of French Guianan forests

The diets of the acouchy Myoprocta exilis, agouti Dasyprocta leporina and paca Agouti paca, the three largest terrestrial rodents of French Guiana forests, were investigated from stomachs collected over several years. These species are primarily frugivores. The percentage of fruit in their diet decreased, and seasonal variation increased from the smallest species, the acouchy, to the largest, the paca (contents in dry mass: respectively, 98.5% ± 0.6%, 87.4% ± 3.5%, and 83.9% ± 7.6%). They differed from each other in the proportions of pulp and secondary foods (leaves, fibre, insects) consumed annually as well as seasonally. Dietary diversity in the acouchy was half that of the two other species. The seasonal variation in consumption of different fruit parts and of secondary foods by these species corresponded well with the fruit production in the forest, and was linked to their reproductive events. Overall, the diets of these three large rodents appeared intermediate between the small rodent species and the artiodactyls (peccaries and brocket deer) inhabiting the same areas, which also concords with their body mass and their place within the guild of terrestrial mammals.

QUIRÓPTEROS Y PEQUEÑOS ROEDORES DE LA RESERVA DE LA BIOSFERA RÍA CELESTÚN, YUCATÁN, MÉXICO

The information available on diversity of mammals in Natural Protected Areas of Yucatan, Mexico has been poorly documented. Between October 2001 and March 2002 we sampled bats and small rodents in three vegetal associations from Ría Celestún Biosphere Reserve. In total we captured 12 species: seven bat species being Dermanura phaeotis the most abundant in the dry forest, and five small rodent species were found being Peromyscus yucatanicus more abuntant into hummock forest (peten). The habitat with highest specific richness of bats was the dry forest (H’=1.39) while peten was to small rodents (H’=0.838). Finally we made the second report of Chiroderma villosum in Yucatan state.

Factors Driving Small Rodents Assemblages from Field Boundaries in Agricultural Landscapes of Western France

In this study, we investigated the factors driving diversity and abundance of small rodent species inhabiting permanent linear habitat patches within high-intensified agricultural landscapes of western France. Multivariate (co-inertia) analysis was used to analyse relationships of habitat and landscape descriptive variables with rodent records. Two main ecological gradients were recognized according to statistical analysis. Relationships of species occurrence with environmental factors were interpreted according to their main life traits. The first ecological gradient clearly differentiated communities from hedges to those of grass-dominated linear banks. This first gradient was associated with the prevalence of forest versus grassland rodent species. This partitioning seems to reflect rather ecological requirements of species than competitive interactions. Small rodents diversity and abundance were inversely evolving along this gradient. The second factor influencing species assemblages was associated to landscape heterogeneity surrounding the permanent habitats. According to this second gradient, species seemed to be selected in relation to their ability to disperse and to use cultivated fields. Maximum diversity was generally observed in heterogeneous permanent habitats with mixed vegetation structure but hedges are important to produce biomass for predators.

Molecular Screening of Bartonella Species in Rodents from the Russian Far East

A potentially broad-range PCR system for gltA gene amplification has been designed. A nearly full (992 bp) sequence of the gltA gene was amplified in two steps. DNA was extracted from organs (spleen and liver) of four mostly spread species of rodents: Apodemus agrarius and Apodemus peninsulae mice; Clethrionomys rufocanus and Microtus fortis voles. All amplicons have been sequenced. The incidence of Bartonella species in rodents was 73%, 60%, 60%, and 83% for the above-mentioned rodents, respectively. Several genotypes have been identified, including two gltA genotypes close to B. taylorii, four gltA genotypes close to B. grahamii, and one genotype of a potentially new species. Several Bartonella species were found in both mice species, although each vole species harbored a single species of Bartonella. High incidence of Bartonella infection was found in all studied species of small rodents in the Russian Far East. Several amplified genotypes probably belong to local strains of B. taylorii and B. grahamii, and one genotype represents a possible new species.

SIGNIFICANCE OF BLARINA BREVICAUDA AS A PREDATOR AND SOURCE OF TRAP-CAPTURE BIAS ON SMALL MAMMALS

Evidence on whether the northern short-tailed shrew (Blarina brevicauda) is a significant predator or a source of bias in trap-capture success of small mammals is contradictory. We compared subsequent captures of 2 murid rodent species (Clethrionomys gapperi and Peromyscus maniculatus) after capture of either murid species or B. brevicauda by using 4 years of capture-release data from New Brunswick, Canada. Capture success for P. maniculatus in a trap after occupancy by B. brevicauda was 65% lower than expected, and for C. gapperi, 67% lower than expected. The response by C. gapperi and P. maniculatus to odors of a different species was similar to their response to odor of B. brevicauda. Although we conclude that examination of odor-response data does not permit a conclusion as to whether B. brevicauda is a significant predator, the ubiquitous distribution of B. brevicauda implies that their influence on trap-capture success is significant, particularly in forests where small-rodent species are of similar weight to B. brevicauda.

Sheep grazing and rodent populations: evidence of negative interactions from a landscape scale experiment

Inter-specific competition, facilitation and predation influence herbivore assemblages, but no study has experimentally explored the interactions between large ungulates and small rodents. In a fully replicated, landscape scale experiment, we manipulated densities of domestic sheep in mountain pastures in Norway. We then determined population growth and densities of rodents by live trapping in each of the areas with different sheep densities. We found that the (summer) population growth rate and autumn density of the field vole (Microtus agrestis) was lower at high sheep density. This provides the first experimental evidence of negative interactions between an ungulate and small rodent species. There was no effect on the bank vole (Clethrionomys glareolus), whose diet differs from sheep. Sheep density, therefore, potentially alters the pattern of inter-specific population synchrony amongst voles. Our study shows that negative interactions between large ungulates and small rodents may be species-specific and negative population consequences for the rodent population appear above threshold ungulate densities.

ECTOPARASITES AND OTHER EPIFAUNISTIC ARTHROPODS OF SYMPATRIC COTTON MICE AND GOLDEN MICE: COMPARISONS AND IMPLICATIONS FOR VECTOR-BORNE ZOONOTIC DISEASES

Ectoparasite and epifaunistic arthropod biodiversity and infestation parameters were compared between 2 sympatric small rodent species, the cotton mouse (Peromyscus gossypinus (Le Conte)) and golden mouse (Ochrotomys nuttalli (Harlan)), in southern Georgia from 1992 to 2003. Because the cotton mouse is known to be a reservoir of more vector-borne zoonotic pathogens than the golden mouse, we hypothesized that it would be parasitized by more ectoparasites that are known to be vectors of these pathogens. Cotton mice (n = 202) were parasitized by 19 species of arthropods, whereas golden mice (n = 46) were parasitized by 12 species. Eleven species of arthropods were recovered from both host species, whereas 7 were recorded only from cotton mice, and 1 species only from golden mice. Infestation prevalences (percent of mice parasitized) were significantly higher for 1 species of arthropod (the tropical rat mite Ornithonyssus bacoti (Hirst)) infesting cotton mice and for 4 species (the flea Peromyscopsylla scotti Fox and the mites Glycyphagus hypudaei Koch, Androlaelaps casalis (Berlese), and Androlaelaps fahrenholzi (Berlese)) infesting golden mice. Mean intensities (mean per infested mouse) were significantly higher for 2 species (the flea Orchopeas leucopus (Baker) and the blacklegged tick Ixodes scapularis Say) infesting cotton mice and for 2 species (G. hypudaei and A. fahrenholzi) infesting golden mice. Ectoparasites that are known to be vectors of zoonotic pathogens were significantly more common on cotton mice than on golden mice. These ectoparasites included the rhopalopsyllid flea Polygenis gwyni (Fox), a vector of the agent of murine typhus; I. scapularis, the principal vector of the agents of Lyme borreliosis, human granulocytic ehrlichiosis, and human babesiosis; and O. bacoti, a laboratory vector of several zoonotic pathogens. However, 2 species of ixodid ticks that can transmit zoonotic pathogens were recovered from both host species. These were the American dog tick Dermacentor variabilis (Say), the principal vector of the agent of Rocky Mountain spotted fever in eastern North America, and Ixodes minor Neumann, an enzootic vector of the agent of Lyme borreliosis. Overall, the cotton mouse was parasitized by significantly more ectoparasites that are known to be vectors of zoonotic pathogens than was the golden mouse. These data support the hypothesis that the cotton mouse has greater epidemiological importance for zoonotic vector-borne pathogen transmission than does the golden mouse.

A new species of Calomys (Rodentia, Sigmodontinae) from Central Brazil identified by its karyotype.

Ten species of small rodents of genus Calomys are found in South America. Three of these ten species are known to occur in Brazil: C. tener, C. laucha and C. expulsus (= C. callosus expulsus). Almost all Calomys karyotypes are made up of acrocentric pairs. In this paper we describe a new karyotype with 2n = 46 (FN = 66), including 11 meta/submetacentric and 11 acrocentric autosomal pairs. This is not related to any described Calomys karyotype. The X chromosome is a medium submetacentric and the Y is a small acrocentric. This new karyotype is briefly compared to karyotype of the sympatric species C. tener (2n = 66, FN = 66). The reduced diploid number and small amount of pericentromeric heterochromatin observed in the biarmed chromosomes that contrasts to large blocks seen in acrocentrics seem to indicate that centric fusion and loss of constitutive heterochromatin have led to the new karyotype. Cytogenetic evidence suggests strongly that a new species with 2n = 46 from Central Brazil should be described in the genus Calomys.

Contrasting effects of fire on populations of two small rodent species in fragments of Atlantic Forest in Brazil

Habitat fragmentation causes a sharp increase in the forested area affected by edge effects (Murcia 1995). Compared with the core of the forest, edges present higher litterfall rates, air and soil humidity reduction, higher temperature and increased wind incidence (Bierregaard et al. 1992, Didham & Lawton 1999, Laurance et al. 1998, Matlack 1993). These features of edges may increase the probability of fire occurrence, especially if the surrounding vegetation is composed of grasses (D'Antonio & Vitousek 1992, Freifelder et al. 1998). After a fire, the damaged edge will grow substantial amounts of herbaceous vegetation, extending the inflammable area into the forest, and thereby creating a positive feedback system of fire susceptibility and intensity (Cochrane & Schulze 1999, Cochrane et al. 1999). Fires may affect the structure and composition of the vegetation (Cochrane & Schulze 1999, Didham & Lawton 1999, Sanaiotti & Magnusson 1995), favouring, in the long-term, the dominance of the community by species characteristic of disturbed habitats and making the habitat unsuitable to primary forest species (Malcolm 1994, Possingham et al. 1994). Unfortunately, there are few studies on the effects of fires on neotropical small-mammal populations (Borchert & Hansen 1983, Ojeda 1989, Vieira & Marinho-Filho 1998). The objective of this study was to analyse the influence of a fire on populations of two rodent species, Akodon cursor (Winge) and Oecomys concolor (Wagner) in two fragments of Atlantic Forest in Brazil.

Daily variation of body temperature, locomotor activity and maximum nonshivering thermogenesis in two species of small rodents

Many mammals are known to have clear circadian rhythms of body temperature ( T b). Large parts of the rhythms correspond to the oscillation of locomotor activity, but this activity does not explain the entire variation of T b. We tested to what extent daily variation of nonshivering thermogenesis (NST), the most important source of heat in small mammals, may elucidate T b oscillations in rodents. We studied daily variation of body temperature, locomotor activity, the rate of NST (MMR NST; measured as a maximum response to noradrenaline (NA)) and resting metabolic rates in thermoneutral ambient temperature (RMR TNZ) in two rodent species: yellow-necked mouse Apodemus flavicollis and root vole Microtus oeconomus. Both species were nocturnally active in our study. Mice had a clear circadian rhythm of T b with minimum of 36.6±0.2°C at 8:00 and maximum of 38.1±0.3°C at 23:00, corresponding to the variation in RMR TNZ. Their MMR NST also exhibited significant daily variation, with the greatest response to NA between 16:00 and 19:00, when T b rising and activity was still low before the onset of the dark phase. High level of MMR NST at this time corresponded with elevated resting metabolic rates below thermoneutrality, but not RMR TNZ. The smallest response to NA was recorded at the time of low T b. In voles the lack of circadian T b variation (average of 38.6±0.1°C) was associated with no variation in MMR NST or RMR TNZ, and contrasted with a clear rhythm of locomotor activity. Our results indicate that NST plays more important role than activity in shaping circadian rhythm of T b.

Biochemical and physiological validation of a corticosteroid radioimmunoassay for plasma and fecal samples in oldfield mice ( Peromyscus polionotus)

The measurement of fecal steroids provides an increasingly important noninvasive technique for assessing reproduction, environmental stress, and aggression in populations of captive and free-living animals. In this paper, we validated the corticosterone (CORT) 125I-radioimmunoassay (ICN Pharmaceuticals) for plasma and fecal samples in a small rodent species, the oldfield mouse ( Peromyscus polionotus subgriseus). The biochemical validations indicated that the assays accurately measured CORT concentrations in the plasma and corticosteroid concentrations in the feces. Physiological validation demonstrated that: (1) blood samples collected within 3 min of disturbing an animal's cage represented “baseline” CORT concentrations, and (2) fecal corticosteroid concentrations collected over a 24-h period closely tracked plasma CORT concentrations approximately 4 h earlier. These results demonstrate that the plasma CORT and fecal corticosteroid assays are sensitive enough to detect biologically meaningful alterations in corticosteroid concentrations in oldfield mice.

Influence of roads on small rodents population in fragmented forest areas, South Korea

The road effect on small rodent population is investigated at 8 fragmented forest areas in the Baekdudaegan mountain range, South Korea in September 2001. We especially focused on the distribution and body condition of small rodents near the roads. Korean field mouse (Apodemus peninsulae) seems to be more sensitive to the existence of a road than striped field mouse (Apodemus agrarius). Korean field mouse prefers interior forest area to around road. Striped field mouse is a habitat generalist and has wide distributional range around road, but Korean field mouse is forest-inhabiting species and their distribution is limited in forest area. These results suggest the effect of road is different on each small rodent species and their habitat preferences.

Second‐order feedback and climatic effects determine the dynamics of a small rodent population in a temperate forest of South America

AbstractThe multiannual cyclic fluctuations exhibited by arvicoline rodents in the Northern Hemisphere have attracted the attention of population ecologists. However, despite the abundant information on small rodent dynamics in South America, there are no studies reporting cyclic population dynamics. Here, we report evidence of cyclic population dynamics in a South American small rodent, the longhaired field mouse (Abrothrix longipilis) from southern temperate forests in Chile. The time‐series analyses showed that longhaired field mice dynamics are better represented by a second‐order autoregressive model characterized by 3‐year cyclic dynamics. The 3‐year cycles are clearly shown in the autocorrelation factor (ACF) pattern and in the dominant frequency of the spectral analysis. In addition, we determined nonlinear effects of the Antarctic Oscillation Index (AAOI). The results shown here pointed out that we need the integration of studies about cyclic small rodent populations from the different continents and beyond the Northern Hemisphere to resolve the enigma underlying the cyclic population dynamics exhibited by many small rodent species.

Demographic dynamics of a neotropical small rodent (Phyllotis darwini): feedback structure, predation and climatic factors

Summary The leaf‐eared mouse (Phyllotis darwini) exhibits large numerical fluctuations associated with high‐ and low‐rainfall years in semi‐arid Chile. Using capture–mark–recapture (CMR) statistical modelling, we provide a detailed description of the demographic variation in this species. We studied between‐year and seasonal variation of demography, and tested for the relative importance of endogenous and exogenous factors as covariates of survival, recruitment, maturation and reproduction over a 12‐year period. The demographic variables studied show larger between‐year than within‐year (seasonal) variation, emphasizing the importance of this source of external variability. We found that both feedback structure and exogenous factors operate together on different demographic processes of this species. We found positive direct feedback effects on survival rate and negative feedback on recruitment, fraction of reproductive individuals and female maturation rates. The ratio between barn and magellanic horned owls showed an important effect on most of the demographic variables of leaf‐eared mice, in particular by influencing negatively survival rates and the fraction of reproductive individuals, thus suggesting the importance of non‐lethal predation. Hence, feedback intrinsic mechanisms (density‐dependence), owls and climate (rainfall and Southern Oscillation Index (SOI)) operate simultaneously in determining the demography of leaf‐eared mice. We hypothesize that trophic interactions with owls (and perhaps other predators) may cause second‐order feedback responses in demography and population dynamics of this small rodent species.

Resource availability and population dynamics of Nicrophorus investigator, an obligate carrion breeder

Summary1. Food resources for rearing young may influence insect populations. This is particularly true for insects that breed obligately on rare, ephemeral resources such as dung, fungi, or carrion.2. Beetles in the genus Nicrophorus bury small vertebrate carcasses for rearing their young. Studies reviewed by Scott (1998) have found a positive relationship between carcass mass and total brood size. It is likely that access to carcasses suitable for breeding, and not food or mates, limits reproduction in both male and female Nicrophorus. Thus, small mammal densities could determine Nicrophorus population sizes.3. The work reported here examined the relationship between Nicrophorus investigator (Coleoptera: Silphidae) population size and small mammal abundance at two sites over a 4‐year period.4. Nicrophorus investigator buried and reared young on all the native small rodent species trapped at two sites in south‐western Colorado, U.S.A. (Peromyscus maniculatus, Microtus montanus, Zapus princeps, Tamias minimus, Thomomys talpoides). They preferred to bury and reproduce on rodent carcasses weighing between 16 and 48 g; rodents of this size represented 82% of captures.5. Population sizes of N. investigator and small rodents were estimated simultaneously using mark‐recapture censuses over a 4‐year period. Considering only rodents within the size range used by N. investigator, the estimated small mammal biomass per hectare in one year and the beetle population size in the following year were correlated significantly.

European Reservoir Hosts of Borrelia burgdorferi sensu lato

Existing knowledge on reservoir hosts of Borrelia burgdorferi sensu lato was collated and reviewed and several species, particularly birds, were identified as reservoir competent. At the present time, 9 small mammals, 7 medium-sized mammals and 16 bird species, including passerines, sea birds and pheasants, appear to be capable of transmitting spirochaetes to ticks and thus of participating in the natural circulation of B. burgdorferi s.l. in Europe. The house mouse, Mus musculus is strongly suspected of reservoir competence and many other small rodent species, particularly in eastern Europe and Russia, have been implicated. Ungulates are not thought to play a major role as reservoir hosts, though co-feeding transmission may permit some tick infection. The criteria for establishment of reservoir status are outlined and a method for identification of host blood meals of previous instars of unfed ticks, developed in a participant laboratory, is briefly described.