Small Rodent Species Research Articles

Habitat use by corn mice (Calomys musculinus) in cropfield borders of agricultural ecosystems in Argentina

Context Calomys musculinus (Cricetidae, Sigmodontinae) is a small rodent species widely distributed in Argentina and particularly abundant in agroecosystems of the Pampean region, where it is known to select border habitats over cropfields. Aims The aim of the present research was to assess habitat use by C. musculinus in cropfield borders. Assuming that the number of rodent captures in each border reflects the intensity of use, we intended to identify the habitat characteristics that would account for abundance differences among borders. Methods Seasonal trapping sessions were carried out in borders of the rural zone of Chucul, Córdoba. Environmental variables were registered from both field surveys and remote-sensing imagery. Generalised linear models were used to identify the habitat variables associated with C. musculinus habitat use. Key results General fit of the models was fairly good; spring, summer and autumn models explained more than 55% of the variation in C. musculinus abundance among borders. Individual plant species were significant predictors of C. musculinus abundance, but they varied with seasons, whereas tree cover and border width were significant predictors in most seasons studied. In general, rodent abundance was positively associated with peanut and maize crops or maize stubbles and negatively related to soybean or its stubbles. In the coldest seasons, rodent abundance increased with increasing land-surface temperature of the border. Conclusions Border use by C. musculinus appeared to respond to differences in border quality, which seems to be more affected by those environmental characteristics that entail a reduction of the predatory risk rather than by those that involve food supply. Crop-fields may partially afford C. musculinus food requirements. Implications Because C. musculinus is the natural reservoir of a zoonotic agent, the identification of the habitat characteristics affecting rodent population numbers in borders may be of crucial importance for the implementation of ecologically based rodent-management strategies aimed at reducing human–rodent contacts. We suggest that wide borders, particularly those contiguous to maize and peanut cropfields, should be understood as priority sites for the implementation of specific control actions.

Effects of the mitochondria-targeted antioxidant SkQ1 on lifespan of rodents

The effect of the mitochondria-targeted, plastoquinone-containing antioxidant SkQ1 on the lifespan of outbred mice and of three strains of inbred mice was studied. To this end, low pathogen (LP) or specific pathogen free (SPF) vivaria in St. Petersburg, Moscow, and Stockholm were used. For comparison, we also studied mole-voles and dwarf hamsters, two wild species of small rodents kept under simulated natural conditions. It was found that substitution of a LP vivarium for a conventional (non-LP) one doubled the lifespan of female outbred mice, just as SkQ1 did in a non-LP vivarium. SkQ1 prevented age-dependent disappearance of estrous cycles of outbred mice in both LP and non-LP vivaria. In the SPF vivarium in Moscow, male BALB/c mice had shorter lifespan than females, and SkQ1 increased their lifespan to the values of the females. In the females, SkQ1 retarded development of such trait of aging as heart mass increase. Male C57Bl/6 mice housed individually in the SPF vivarium in Stockholm lived as long as females. SkQ1 increased the male lifespan, the longevity of the females being unchanged. SkQ1 did not change food intake by these mice. Dwarf hamsters and mole-voles kept in outdoor cages or under simulated natural conditions lived longer if treated with SkQ1. The effect of SkQ1 on longevity of females is assumed to mainly be due to retardation of the age-linked decline of the immune system. For males under LP or SPF conditions, SkQ1 increased the lifespan, affecting also some other system(s) responsible for aging.

The diet of migrant Red Kites Milvus milvus during a Water Vole Arvicola terrestris outbreak in eastern France and the associated risk of secondary poisoning by the rodenticide bromadiolone

Poisoning by pesticides is considered one of the primary threats to the Red Kite Milvus milvus. We studied the diet of this raptor in an area of eastern France where the rodenticide bromadiolone is widely used to control Water Vole Arvicola terrestris outbreaks. A high degree of specialization for Water Voles was noted, as their remains were identified in all 119 pellets collected in autumn 2008, whereas other small rodent species and insects occurred in 27 and 9% of pellets, respectively. We estimated that Water Voles constituted 94% of the total biomass ingested by Red Kites under these conditions. Based on these data, the risk of secondary poisoning due to feeding on poisoned voles was assessed. Acute exposure on a single day was not considered a risk for Kites, but exposure to poisoned voles over 1 week represented the maximal risk for the Red Kite; the calculated dose of bromadiolone ingested by a Red Kite was 137 times higher than the toxicological benchmark for birds. A field survey in the studied area detected four dead Red Kites and one moribund bird in autumn 2008 but did not confirm that the cause of death was bromadiolone poisoning. We suggest that professional monitoring is needed to assess the impact of rodenticides on Red Kites in areas where voles are controlled.

Dynamics and reproduction of small rodents in Germany

Analyses of time series of population dynamics and reproduction of small rodent species in Germany show that 1) first order effects prevail and higher order effects occur, 2) that within and across species abundance can fluctuate synchronously and 3) that part of the density dependence may be explained by intra-specific mechanisms related to reproduction.

Reproduction and ontogeny of Mastacomys fuscus (Rodentia: Muridae) in the Australian Alps and comparisons with other small mammals living in alpine communities

Two species of small rodents, Mastacomys fuscus and Rattus fuscipes, and one small dasyurid marsupial Antechinus swainsonii live sympatrically in the subalpine habitat of SE Australia. This paper describes the reproductive characteristics and ontogeny of M. fuscus, and shows that the three species have different reproductive strategies that, in part, are a reflection of their different phylogenies. Cold and snow in winter, and a short summer season, limit the length of time available for reproduction and development. The rodent species exhibit similar reproductive characteristics to those in alpine regions of Europe, North America and South Africa.

Dynamics of incisor growth and daily increments on the incisor surface in three species of small rodents

The lower and upper incisors has been studied in striped field mice (Apodemus agrarius), yellow-necked mice (A. flavicollis), and migratory hamsters (Cricetulus migratorius) trapped in the Volgograd Region from April to March. The incisors of all animals have been found to have a striated surface, with series of slight ridges and grooves. As shown by analyzing the incisors of animals labeled with tetracycline, these are daily increments of dentin. The total numbers of increments (the period of complete tooth renewal) in the upper and lower incisors of the same animal are similar, but the degrees of their distinctness can be different. The number of daily increments increases but their width (daily growth rate) decreases with age even in adult animals and, in addition, varies by seasons. These two trends—the decrease in tooth increment with age and its seasonal variation—have proved to mask each other when an uneven-aged sample of animals trapped over several months is studied. Therefore, the season of death of an animal cannot be reliably estimated from the width of daily tooth increment unless the age of this animal is taken into account. The increment width in young animals in autumn may be the same as in older animals in spring and summer. In attempts to use the incisor surface sculpture for determining the season of animal death, it is necessary to separate the young from adults (at least by the criterion of incisor length). The decrease of increment width with age and its seasonal variation in the absence of obvious changes in the diet and pattern of incisor attrition indicate that the incisor growth rate is subject to age-dependent and seasonal changes, as is the growth rate of the organism as a whole. The distinctness and internal structure of daily increments also vary depending on animal age and species, which is due apparently to differences in the circadian rhythms of incisor growth. The presence of one or, less frequently, several grooves within a daily increment, which has occurred in all species studied, is evidence for not only circadian but also ultradian rhythms in the growth of incisors.

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.

Interspecific variability in the abundance of small rodents in the highlands of Chiapas, Mexico

En este estudio proporcionamos datos sobre la abundancia y composicion de especies de pequenos roedores durante un ciclo anual en cuatro localidades representadas por dos habitats contrastantes: cultivos de maiz y Reservas Ecologicas, en el Municipio de San Cristobal de Las Casas, Chiapas. Se registraron en total 469 capturas de nueve especies de roedores muridos, de las cuales las mas abundantes fueron Reithrodontomys fulvescens, Sigmodon hispidus y Peromyscus levipes. El mayor numero de capturas (272) se registro durante la epoca seca y la mayor riqueza de especies (7) durante la epoca de lluvia en un area agricola. Encontramos diferencias significativas en el numero de capturas en epoca seca y de lluvia solamente para la Reserva Ecologica Moxviquil

Redundant or complementary? Impact of a colonizing species on community structure and function

Recent studies suggest that species with similar functional traits will have similar effects on ecosystems, but evidence for redundancy of species impacts is limited. Here we use a long-term experiment to gain insight into functional relationships within a desert rodent community. Experimental removal of kangaroo rats, Dipodomys spp., coupled with the recent, serendipitous colonization of a single species of large pocket mouse Chaetodipus baileyi yielded treatments that differed in the diversity of large granivorous rodents present. We evaluated functional overlap of C. baileyi and the other resident large granivores (i.e. the kangaroo rats) by comparing total energy use of granivorous rodents and total abundance and species richness of small granivores across treatments before and after the arrival of C. baileyi. We found that C. baileyi almost completely compensated for the changes in these key ecosystem-level properties caused by kangaroo rat removal, but it differentially impacted the population dynamics of individual small granivorous rodent species. Thus, its effects were largely complementary, rather than redundant, to those of the missing kangaroo rats. Although short-term or single-measure analyses may suggest redundancy, our results support the longstanding dictum that niches of coexisting species are often similar but rarely, if ever, identical.

Rodent and Flea Abundance Fail to Predict a Plague Epizootic in Black-Tailed Prairie Dogs

Small rodents are purported to be enzootic hosts of Yersinia pestis and may serve as sources of infection to prairie dogs or other epizootic hosts by direct or flea-mediated transmission. Recent research has shown that small rodent species composition and small rodent flea assemblages are influenced by the presence of prairie dogs, with higher relative abundance of both small rodents and fleas at prairie dog colony sites compared to grasslands without prairie dogs. However, it is unclear if increased rodent or flea abundance predisposes prairie dogs to infection with Y. pestis. We tracked rodent and flea occurrence for 3 years at a number of prairie dog colony sites in Boulder County, Colorado, before, during, and after a local plague epizootic to see if high rodent or flea abundance was associated with plague-affected colonies when compared to colonies that escaped infection. We found no difference in preepizootic rodent abundance or flea prevalence or abundance between plague-positive and plague-negative colonies. Further, we saw no significant before-plague/after-plague change in these metrics at either plague-positive or plague-negative sites. We did, however, find that small rodent species assemblages changed in the year following prairie dog die-offs at plague-affected colonies when compared to unaffected colonies. In light of previous research from this system that has shown that landscape features and proximity to recently plagued colonies are significant predictors of plague occurrence in prairie dogs, we suggest that landscape context is more important to local plague occurrence than are characteristics of rodent or flea species assemblages.

Small Mammals Associated with Colonies of Black-Tailed Prairie Dogs (Cynomys ludovicianus) in the Southern High Plains

We compared diversity and abundance of small mammals at colonies of black-tailed prairie dogs (Cynomys ludovicianus) and paired non-colony sites. Of colonies of black-tailed prairie dogs in our study area, >80% were on slopes of playa lakes; thus, we used sites of colonies and non-colonies that were on slopes of playa lakes. We trapped small mammals on 29 pairs of sites. Overall abundance did not differ between types of sites, but some taxa exhibited associations with colonies (Onychomys leucogaster) or non-colonies (Chaetodipus hispidus, Reithrodontomys, Sigmodon hispidus). Diversity and evenness of small mammals did not differ between colonies and non-colonies in 2002, but were higher on non-colonies in 2003. Although we may not have detected some rare or infrequently occurring species, our data reveal differences in diversity and evenness of more common species among the types of sites. Prairie dogs are touted as a keystone species with their colonies associated with a greater faunal diversity than adjacent lands. Our findings contradict several studies reporting greater diversity and abundance of small mammals at colonies of prairie dogs. We suggest that additional research across a wider landscape and incorporating landscape variables beyond the immediate trapping plot may further elucidate interspecific associations between black-tailed prairie dogs and species of small rodents.

Chapter 8. Biodiversity and Biogeography of the Moss-mice of New Guinea: A Taxonomic Revision of Pseudohydromys (Muridae: Murinae)

Morphological investigations involving nearly all available museum material representing New Guinea “moss-mice” (rodents traditionally classified in the genera Pseudohydromys, Neohydromys, Mayermys, and Microhydromys) reveal outstanding undiagnosed taxic diversity (a minimum of 16 species, versus the eight species previously described) and allow for redefinition of generic boundaries among these little-studied rodents. Apart from Microhydromys Tate and Archbold, 1941 (comprising two species, as recently revised by Helgen et al., in press), herein we recognize two genera of New Guinea moss-mice: Pseudohydromys Rümmler, 1934 (now incorporating Neohydromys Laurie, 1952, Mayermys Laurie and Hill, 1954, and “Microhydromys” musseri Flannery, 1989) and a newly described genus, Mirzamys. Species of Pseudohydromys are recorded from montane areas throughout New Guinea (elevations spanning 600 to at least 3800 meters), including the mountain ranges of the Central Cordillera, the Huon Peninsula, and the North Coastal ranges. We diagnose and review 12 species of Pseudohydromys, including six species described as new. The new genus Mirzamys is erected to accommodate two newly described species of small terrestrial rodents from middle and upper montane forests and subalpine grassland edges (1900–3450 m) in the mountains of central New Guinea. Together these two new species represent a distinctive hydromyin lineage that resembles the terrestrial New Guinea hydromyin genera Pseudohydromys and Paraleptomys in various traits. Ecological attributes of all recognized moss-mice taxa, both previously and newly described, are reviewed in light of all information currently available about their biology.

Multi‐annual density fluctuations and habitat size enhance genetic variability in two northern voles

In order to gain a better understanding of the consequences of population density cycles and landscape structure for the genetic composition in time and space of vole populations, we analyzed the multiannual genetic structure of the two numerically dominant, sympatric small rodent species of northernmost Fennoscandia. Red volesMyodes rutilusand grey‐sided volesM. rufocanuswere trapped in the subarctic birch forest along three fjords over five years. Along each fjord, there were four or five altitudinal transects each with five trapping stations. Spring and fall population densities were estimated from mark–recapture data. Grey‐sided voles exhibited higher amplitude density fluctuations than red voles. Polymorphism at eight or nine microsatellite loci, determined in 1228 voles, was used to estimate local genetic diversity and differentiation among samples. Genetic diversity was higher in grey‐sided voles than in red voles. Spring densities had no effect on local genetic diversity or on differentiation. The amplitude of density fluctuations and the extent of favorable habitat (sub‐arctic birch forest) surrounding each site had a positive effect on genetic diversity, and the amplitude of density fluctuations had a negative effect on differentiation in red voles, for which fluctuating populations were compared with more stable populations. The harmonic mean of densities, reflecting average population sizes, had a negative effect on genetic diversity in red voles, but a positive effect in grey‐sided voles, for which only fluctuating populations were compared. No other effects were significant for grey‐sided voles. A temporal assignment test showed that the spatial structure was more stable in time for populations with more stable population dynamics. Altogether our results suggest that high amplitude density fluctuations lead to more gene flow and higher genetic diversity in vole populations.

There's a Rat in My Room! Now What? Mice Show No Chronic Physiological Response to the Presence of Rats

In general, guidelines on housing and care of animals in the laboratory state that rats and mice should not be housed in the same room. Mice may perceive rats as predators. Although one theory says this can cause stress, there is little scientific evidence to support this theory. In the wild, rats and mice usually do not share the same microhabitat, but this appears to be true for most small rodent species. Furthermore, reports of predatory behavior of rats toward mice mainly originate from experimental settings using rats with high inbred levels of aggression. This experiment measured heart rate (HR), body temperature (BT), activity (AC), and urinary corticosterone in female C57BL/6 mice before, during, and after introducing Wistar rats into their room. The study found no chronic effects of rat introduction on any parameters. The study concluded that housing rats and mice in the same room is at least less disturbing than cage cleaning, which caused a temporary increase of HR, BT, and AC. Current results do not support legislation based on compromised welfare.

Host Records for the Immature Stages of the South American Tick,Amblyomma fuscum(Acari: Ixodidae)

2 ABSTRACT: This work reports free-living opossums (Didelphis aurita and Didelphis albiventris) and a rodent species (Thrichomys laurentius) naturally infested by the immature stages of Amblyom- ma fuscum Neumann, 1907 in Brazil. Previously the only host record for the A. fuscum immature stages was for a single nymph collected on an opossum D. aurita in the state of Sao Paulo. Herein are presented two new host records (D. albiventris and T. laurentius) for A. fuscum. Our results indi- cate that opossums (Didelphis spp.), and one small rodent species (T. laurentius) are major hosts for immature stages of A. fuscum in Brazil. Based on the known feeding habits of immature stages of A. fuscum, coupled with previous reports of the adult stage parasitizing humans, A. fuscum is a poten- tial vector of spotted fever group rickettsiae.

Niche separation between the weasel Mustela nivalis and the stoat M. erminea in Belarus

We investigated three main niche components (diet composition, habitat use and diel activity rhythms) to examine how the weasel Mustela nivalis and the stoat M. erminea, both specialised predators of small rodents, could permanently coexist in Belarus. Our research was carried out in temperate forests of Belarus, in two study areas with different environmental conditions: 1) continuous dry-land forest interspersed by a variety of swampy biotopes and aquatic ecosystems (Paazerre, northern Belarus) and 2) extended wetland with large forest patches (Palesse, southern Belarus). The habitat use and diel activity rhythms of seven weasels and eight stoats were analysed by radio-tracking over about 300 km2 in Paazerre. Snow-tracking was also applied to study habitat use by the two mustelid species. Diet composition was examined by analysing 365 weasel scats and 606 stoat scats. Our results suggest that while the weasel and stoat occur in close proximity to each other, they use different micro-habitats, are most active during different times of the day, and prey primarily on different small rodent species. Most weasels selected forest and forest edge habitats, where they predominantly preyed on smaller rodent species (bank voles Clethrionomys glareolus and Apodemus mice); stoats selected wetlands, especially open grassy marshes, and preyed more frequently on larger rodents such as water voles Arvicola terrestris and Microtus voles. Weasels were mostly diurnal and adjusted their activity to the seasonally changing length of daylight, whereas stoats were much more active in twilight and during the night.

Hair structure of small rodents from central Argentina: A tool for species identification

Mammal hairs differ among species and may therefore be used for diagnoses at the species level. We characterized dorsal guard hairs of most small rodent species that may be found in central Buenos Aires province (Argentina), according to their geographic distribution: Cavia aperea , Rattus rattus , R. norvegicus , Mus musculus , Holochilus brasiliensis , Scapteromys aquaticus , Oxymycterus rufus , Oligoryzomys flavescens , Akodon azarae , Deltamys kempi , Calomys laucha and C. musculinus . We provide discriminant functions and a dichotomic key to identify hairs at the species level based on hair length and width and scale morphology observed in specific sections of dorsal guard hairs. Discriminant functions require fewer measurements and are faster than the use of the key.

Characteristics of small rodent populations in post-fire silvicultural management stands within pine forest

We examined changes in habitat and densities of three small rodent species, Korean field mice Apodemus peninsulae, Korean large-toothed red-backed voles Eothenomys regulus, and black-striped field mice A. agrarius, in forest burned 4 years earlier with damaged trees removed and with pine Pinus densiflora left unharvested, and in unburned forest. Forest structure was dramatically changed by post-fire silvicultural practices. Coverage of vegetation, number of stand trees, volume of downed coarse woody debris, and number of downed trees were significantly different among study areas. We captured 584 individual small rodents during 90 trap-nights. Mean number of small rodents captured in the unburned forests was significantly higher than burned forests with or without trees removed. Stand-structure was simplified in burned with damaged trees removed stand by post-fire practices. Also, there were more rodents in burned stands which were not harvested than in those in which damaged trees were removed. Because of differences in stand-structure and forest-floor small rodents, post-fire practices in burned stands should be reevaluated. Long-term experiments are needed to elucidate the potential effects of pine forest management strategies after forest fires.

Old mice, young islands and competing biogeographical hypotheses

Naturally occurring variation within a small rodent species native to the southeastern USA, Peromyscus polionotus, has interested biologists for nearly a century. This species has contributed significantly to our understanding of geographical variation and has often been presented as an example of adaptive evolution. Much of the interest in this organism has been predicated on assumptions that the species is relatively young (<300 000 bp) and that coastal populations have a very recent history (<10 000 bp). To test these assumptions and the prevailing biogeographical hypothesis (Recurrent Invasion), we examined nucleotide sequence data from the cytochrome b and D-loop mitochondrial regions (2449 bp) for 79 samples of P. polionotus collected across the Gulf Coast region of Florida and Alabama. Samples representing Peromyscus maniculatus bairdii, P. m. sonoriensis, P. m. pallescens, and P. keeni were used as outgroups. The degree of cytochrome b divergence (approximately 4.4%) between P. maniculatus and P. polionotus was higher than expected. Analyses consistently indicated that three distinct groups are represented within P. polionotus from the Gulf Coast region. Among these, coastal populations (beach mice) form a monophyletic group and apparently represent a substantially older group (approximately 200 000 year. separation) than previously recognized. Our results were counter to the core assumptions of the existing biogeographical model but were consistent with an alternative hypothesis (Shore-line Tracking) which provides a more parsimonious explanation for the observed patterns. This research provides new insight into the evolutionary history of P. polionotus and highlights the importance of considering biogeographical history when evaluating extant patterns of natural variation.

From population structure to genetically-engineered vectors: New ways to control vector-borne diseases?

Epidemiological studies on vectors and the pathogens they can carry (such as Borrelia burgdorferi) are showing some correlations between infection rates and biodiversity highlighting the “dilution” effects on potential vectors. Meanwhile other studies comparing sympatric small rodent species demonstrated that rodent species transmitting more pathogens are parasitized by more ectoparasite species. Studies on population structure and size have also proven a difference on the intensity of the parasitic infection. Furthermore, preliminary results in genetic improvement in mosquitoes (genetic markers, sexing, and genetic sterilization) will also increase performance as it has already been shown in field applications in developing countries. Recent results have greatly improved the fitness of genetically-modified insects compared to wild type populations with new approaches such as the post-integration elimination of transposon sequences, stabilising any insertion in genetically-modified insects. Encouraging results using the Sterile Insect Technique highlighted some metabolism manipulation to avoid the viability of offspring from released parent insect in the wild. Recent studies on vector symbionts would also bring a new angle in vector control capabilities, while complete DNA sequencing of some arthropods could point out ways to block the deadly impact on animal and human populations. These new potential approaches will improve the levels of control or even in some cases would eradicate vector species and consequently the vector-borne diseases they can transmit. In this paper we review some of the population biology theories, biological control methods, and the genetic techniques that have been published in the last years that are recommended to control for vector-borne diseases.