Number Of Rodent Species Research Articles

The diet of commensal Crocidura olivieri (Soricomorpha: Soricidae): predation on co-existing invasive Mus musculus suggested by DNA metabarcoding data

Abstract Crocidura olivieri is a large-sized shrew species showing a clear trend towards commensalism in West Africa, where it co-occurs and interacts with a number of rodent species in indoor small mammal communities. Among the rodents present is the house mouse Mus musculus, a major invasive species worldwide. We here test the hypothesis that M. musculus could be part of the diet of C. olivieri in a number of localities of Senegal where the two species are known to coexist. We use a metabarcoding approach based on the high-throughput sequencing of a 133 bp fragment of the COI gene, on DNA extracted from digestive tracts and faeces of a sample of 108 shrews. Beside insects of various groups (ants, beetles and cockroaches especially) representing usual items of shrew’s diet, and traces of domestic mammals and poultry that were probably scavenged, several species of rodents were evidenced. Among them, M. musculus was by far the best represented species, found in 17 of the 54 shrews where at least one prey taxon was identified. This finding tends to confirm the potential role of C. olivieri as predator of house mice, while highlighting the capacity of this species to adapt its diet to environmental conditions.

Population Density of the White Bellied Rat, Rattus Rattus Frugivorus in El-Kawther City, Sohag Governorate, Egypt

Rodentia is one of the most important mammalian orders which has a great number of rodent species with their effect on the environment. Directly, through their destructive feeding habits

Distributional ecology of Andes hantavirus: a macroecological approach

BackgroundHantavirus pulmonary syndrome (HPS) is an infection endemic in Chile and Argentina, caused by Andes hantavirus (ANDV). The rodent Oligoryzomys longicaudatus is suggested as the main reservoir, although several other species of Sigmodontinae are known hosts of ANDV. Here, we explore potential ANDV transmission risk to humans in southern South America, based on eco-epidemiological associations among: six rodent host species, seropositive rodents, and human HPS cases.MethodsWe used ecological niche modeling and macroecological approaches to determine potential geographic distributions and assess environmental similarity among rodents and human HPS cases.ResultsHighest numbers of rodent species (five) were in Chile between 35° and 41°S latitude. Background similarity tests showed niche similarity in 14 of the 56 possible comparisons: similarity between human HPS cases and the background of all species and seropositive rodents was supported (except for Abrothrix sanborni). Of interest among the results is the likely role of O. longicaudatus, Loxodontomys micropus, Abrothrix olivaceus, and Abrothrix longipilis in HPS transmission to humans.ConclusionsOur results support a role of rodent species’ distributions as a risk factor for human HPS at coarse scales, and suggest that the role of the main reservoir (O. longicaudatus) may be supported by the broader rodent host community in some areas.

Predicting species richness of ectoparasites of wild rodents from the Río de la Plata coastal wetlands, Argentina.

The richness of ectoparasite species associated with Sigmodontinae rodents (Cricetidae) from different sites located in the coastal wetlands of the Río de la Plata in Argentina was predicted by a model with three components: (1) habitat type, considered analogous to rodent species; (2) average ectoparasite species richness on each rodent species, and (3) average number of rodent species parasitized by each ectoparasite species. The model, based on rodent information (number of species and total number of captured rodents) and the environmental gradient, has a reasonably good fit for the observed data as well as independent data from different localities. The model is predictive and robust, and it could be a useful tool for epidemiological and biodiversity management strategies. Furthermore, the model could be adapted to other habitats if a suitable estimate of an environmental gradient is found, and it could be also possible to adapt it to other host taxa.

Indirect food web interactions affect predation of Tengmalm's Owls Aegolius funereus nests by Pine Martens Martes martes according to the alternative prey hypothesis

Although population cycles of rodents are geographically widespread and occur in a number of rodent species, higher‐order food web interactions mediated by predator–rodent dynamics have primarily been described from boreal and arctic biomes. During periods of low rodent abundance, predators may switch to alternative prey, which may affect other predators directly or indirectly. Using a long‐term dataset, we assessed the frequency of Pine Marten Martes martes predation on the nests of Tengmalm's Owl Aegolius funereus during periods of fluctuating rodent abundance in Central Europe. The number of nests predated by Pine Martens was positively correlated with the annual number of nests available. The probability of predation by Pine Martens on Tengmalm's Owl nests decreased with increasing spring abundance index of Apodemus mice, but was not related to the abundance index of Myodes and Microtus voles, pooled rodent abundance or age of the nestbox. Additionally, we found no relationship between the breeding frequency (i.e. the number of nesting attempts per nestboxes available) and an abundance index of Microtus and Myodes voles, Apodemus mice or overall rodent abundance. Our results demonstrate, for the first time in a temperate area, that during periods of low Apodemus mouse abundance, the switching response of an opportunistic mammalian predator can lead to indirect food web interactions through an increase in nest predation on a sympatric avian predator.

A comparison of bats and rodents as reservoirs of zoonotic viruses: are bats special?

Bats are the natural reservoirs of a number of high-impact viral zoonoses. We present a quantitative analysis to address the hypothesis that bats are unique in their propensity to host zoonotic viruses based on a comparison with rodents, another important host order. We found that bats indeed host more zoonotic viruses per species than rodents, and we identified life-history and ecological factors that promote zoonotic viral richness. More zoonotic viruses are hosted by species whose distributions overlap with a greater number of other species in the same taxonomic order (sympatry). Specifically in bats, there was evidence for increased zoonotic viral richness in species with smaller litters (one young), greater longevity and more litters per year. Furthermore, our results point to a new hypothesis to explain in part why bats host more zoonotic viruses per species: the stronger effect of sympatry in bats and more viruses shared between bat species suggests that interspecific transmission is more prevalent among bats than among rodents. Although bats host more zoonotic viruses per species, the total number of zoonotic viruses identified in bats (61) was lower than in rodents (68), a result of there being approximately twice the number of rodent species as bat species. Therefore, rodents should still be a serious concern as reservoirs of emerging viruses. These findings shed light on disease emergence and perpetuation mechanisms and may help lead to a predictive framework for identifying future emerging infectious virus reservoirs.

Classification Tree Methods Provide a Multifactorial Approach to Predicting Insular Body Size Evolution in Rodents

Many hypotheses have been proposed to explain size changes in insular mammals, but no single variable suffices to explain the diversity of responses, particularly within Rodentia. Here in a data set on insular rodents, we observe strong consistency in the direction of size change within islands and within species but (outside of Heteromyidae) little consistency at broader taxonomic scales. Using traits of islands and of species in a classification tree analysis, we find the most important factor predicting direction of change to be mainland body mass (large rodents decrease, small ones increase); other variables (island climate, number of rodent species, and area) were significant, although their roles as revealed by the classification tree were context dependent. Ecological interactions appear relatively uninformative, and on any given island, the largest and smallest rodent species converged or diverged in size with equal frequency. Our approach provides a promising framework for continuing examination of insular body size evolution.

Swim stress-induced ultrasonic vocalizations forecast resilience in rats

Ultrasonic vocalizations (USVs) have been observed in a number of rodent species. They occur under a variety of conditions, including aversive and stressful experiences. In the current study, we recorded USVs emitted by rats exposed to intermittent cold water swim (ICWS) stress and subsequently evaluated their performance in an instrumental swim escape test (SET). In the SET, rats exposed to ICWS fall into two categories, resilient or vulnerable, based on good or poor learning, respectively. Four of 16 rats exposed to ICWS emitted far more USVs during the stress procedure than the remaining 12. Interestingly, in the SET these USV-emitting rats appeared resilient with escape performance comparable to controls while on average the non-emitting rats failed to learn. This result demonstrates that USVs can serve as a predictor of stress resilience. USV screening during stress may serve as a novel and non-invasive strategy to predict subsequent stress reactivity and afford insight into the neural systems involved in resilience.

Tracking genome organization in rodents by Zoo-FISH

The number of rodent species examined by modern comparative genomic approaches, particularly chromosome painting, is limited. The use of human whole-chromosome painting probes to detect regions of homology in the karyotypes of the rodent index species, the mouse and rat, has been hindered by the highly rearranged nature of their genomes. In contrast, recent studies have demonstrated that non-murid rodents display more conserved genomes, underscoring their suitability for comparative genomic and higher-order systematic studies. Here we provide the first comparative chromosome maps between human and representative rodents of three major rodent lineages Castoridae, Pedetidae and Dipodidae. A comprehensive analysis of these data and those published for Sciuridae show (1) that Castoridae, Pedetidae and Dipodidae form a monophyletic group, and (2) that the European beaver Castor fiber (Castoridae) and the birch mouse Sicista betulina (Dipodidae) are sister species to the exclusion of the springhare Pedetes capensis (Pedetidae), thus resolving an enduring trifurcation in rodent higher-level systematics. Our results together with published data on the Sciuridae allow the formulation of a putative rodent ancestral karyotype (2n = 50) that is thought to comprise the following 26 human chromosomal segments and/or segmental associations: HSA1pq, 1q/10p, 2pq, 2q, 3a, 3b/19p, 3c/21, 4b, 5, 6, 7a, 7b/16p, 8p/4a/8p, 8q, 9/11, 10q, 12a/22a, 12b/22b, 13, 14/15, 16q/19q, 17, 18, 20, X and Y. These findings provide insights into the likely composition of the ancestral rodent karyotype and an improved understanding of placental genome evolution.

How does sampling protocol affect the richness and abundance of small mammals recorded in tropical forest? An example from the Atlantic Forest, Brazil

Small mammals are important elements of tropical forests but there is not a protocol for sampling these animals. In this study, we aimed at evaluating which sampling design maximizes the richness and/or the abundance of small mammals in a given area. We used data available in studies carried out in the Brazilian Atlantic forest. The variables analyzed for each study were number of marsupial species, number of rodent species, number of marsupial individuals and number of rodent individuals (dependent variables), sampling effort (trap-nights), design (grid or transect), number of strata sampled, number of nights and number of trap types used (independent variables). We did an analysis of covariance using the type of forest (evergreen or semideciduous) as the co-factor and factoring out the sampling effort to verify if the patterns of richness and abundance of species changed between these types of forests. The same analysis was done using the design as the cofactor in different forest types. Therefore, we performed analyses of variance in each forest type using the number of strata sampled, number of traps types and number of nights as factors to verify the effects of these factors on richness and abundance of the species. The capture effort was the most important variable to explain the richness and abundance of small mammals. The forest type influenced the abundance of species. Marsupials seemed to be more abundant in the semideciduous forest and rodents in the evergreen forest. RJ, Brazil.

Evidence for the influence of testosterone in the performance of spatial navigation in a virtual water maze in women but not in men

Testosterone (T) may be associated with enhanced spatial navigation in a number of rodent species, although the nature of the relation is equivocal. Similarly, numerous studies in humans generally have found that T is associated with enhanced spatial ability on a variety of paper and pencil tasks that may relate to navigational ability. However, relatively few studies have reported effects of T on navigational ability in humans. We investigated the relationship between endogenous T and performance on a virtual water maze (vWM) and mental rotations test (MROT). ELISA for T was performed on salivary samples that were obtained from participants before and after completion of both spatial tasks. Results indicated that women with low T required more time to locate the hidden platform in the vWM than either group of men or women with high T. Significant negative correlations were found for the entire sample between vWM performance and T, and between vWM latency to escape and MROT. Similar significant correlations were found in women but not men. Thus, our data support the position that T improves performance in the vWM in a linear fashion, most strongly in women. However, further work is needed to confirm this hypothesis in humans.

Learned magnetic compass orientation by the Siberian hamster, Phodopus sungorus

Magnetic orientation in mammals has been demonstrated convincingly in only two genera of subterranean mole-rats (Spalax and Cryptomys sp.) by examining the directional placement of nests in radially symmetrical indoor arenas. Mole-rats show a spontaneous directional preference to place their nests to the south or southeast of magnetic north. Using a similar nest-building assay, we show that laboratory-raised Siberian hamsters also use directional information from the magnetic field to position their nests. In contrast to mole-rats, however, the directional preference for nest position shown by Siberian hamsters appears to be learned. Hamsters were housed in rectangular cages aligned along perpendicular axes before testing. When subsequently tested in a radially symmetric arena, the hamsters positioned their nests in a bimodal distribution that coincided with the magnetic direction of the long axis of the holding cages. We also present results from an earlier set of experiments in which hamsters showed consistent orientation only in the ambient magnetic field, and not in experimentally rotated magnetic fields. The conditions under which these earlier experiments were carried out suggest that holding conditions prior to testing and the presence of nonmagnetic cues may influence the expression of magnetic orientation in the Siberian hamster. Failure to consider these and other factors may help to explain why previous attempts to demonstrate magnetic orientation in a number of rodent species have failed or, when positive results have been obtained, have been difficult to replicate. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Geographic distribution patterns of small mammals in Swaziland in relation to abiotic factors and human land-use activity

Swaziland is a small, topographically diverse southern Africa country whose mammalian fauna has been poorly studied. The distributions of small mammals in Swaziland were surveyed at 39 localities. A total of 15 species of rodents and ten species of insectivores were captured during the survey. The number of species of insectivore captured at a locality was positively correlated with mean annual rainfall, while the number of rodent species captured was negatively correlated with altitude. The number of rodent species captured was lower on Swazi Nation Land compared with privately owned land or protected land (reserves). This was probably due to the radical habitat alteration that had taken place on Swazi Nation Land, inter alia overgrazing by livestock, cultivation of maize and deforestation. The effect of this habitat alteration on the number of rodent species was more pronounced in high-lying areas of Swaziland. This may have been due to the fact that a large number of the rodent species inhabiting high-lying areas require thick, tall grassland habitats, whereas many of the low-lying species prefer more open habitats with less grass cover. Since grazing acts to reduce grass cover, it is suggested that the species inhabiting high-lying areas would be more affected by overgrazing, than low-lying species.

Effect of 6‐Methoxy‐2‐Benzoxazolinone on the Activities of Rat Pineal N‐Acetyltransferase and Hydroxyindole‐O‐Methyltransferase and on Melatonin Production

A naturally occurring compound, 6-methoxybenzoxazolinone (6-MBOA), present in grasses, has been shown to induce sexual maturation in a number of rodent species. The structural similarity of 6-MBOA and melatonin has led researchers to suspect that 6-MBOA might induce its progonadal effects by directly altering pineal function. Previous studies have shown that 6-MBOA has the properties of a weak beta-adrenergic agonist capable of stimulating rat pineal N-acetyltransferase (NAT) activity at pharmacological concentrations of 10(-3) M. In the present study we have examined the effect of 6-MBOA on both the pineal melatonin synthesizing enzymes, namely, NAT and hydroxyindole-O-methyltransferase (HIOMT) as well as on melatonin production, in organ cultured rat pineal glands. In addition, we have also examined the ability of 6-MBOA to displace a ligand from rat brain alpha- and beta-adrenoceptors. Our results confirm that 6-MBOA stimulates NAT activity and melatonin production at the high concentration of 10(-3) M. It appears to have no effect on HIOMT activity. A competition study shows that 6-MBOA is able of displacing ligands at the alpha- and beta-adrenoceptors but only at concentrations greater than 10(-4) M. Whether such high concentrations of 6-MBOA reach the pineal of rodent in their natural habitat is unknown. However, if 6-MBOA does mediate progonadal effects by altering pineal function it would be expected that 6-MBOA would ultimately inhibit the effects of melatonin. The possibilities are that the high melatonin levels induced by 6-MBOA cause desensitization of melatonin receptors or that 6-MBOA is an antagonist at the level of the melatonin receptor, thus restricting the inhibitory effects of melatonin on the reproductive system.

Effects of melatonin and 6-methoxybenzoxazolinone on photoperiodic control of testis size in adult male golden hamsters.

Consumption of young plants containing 6-methoxybenzoxazolinone (6-MBOA) appears to play an important role in the initiation of reproduction each spring in wild populations of the montane vole. Following its identification, 6-MBOA has been found to stimulate the reproductive system in a number of rodent species, but the mechanism of action remains unknown. The chemical structure of 6-MBOA is similar to melatonin, which, in addition to its well-known antigonadal effects, can exert a progonadal influence under certain experimental conditions. To determine if 6-MBOA might act as a melatonin agonist, four experiments were conducted to compare the effect of these two compounds on testis size in the golden hamster, a rodent whose responses to melatonin are well characterized. 1) Hamsters exposed to 14 h light per day (14L:10D) received a daily injection of melatonin (25.0 micrograms) or 6-MBOA (17.8 micrograms). 2) Hamsters exposed to 6L:18D received Silastic capsules (50 or 200 mm) containing melatonin or 6-MBOA. 3) Hamsters exposed to 6L:18D received chow containing melatonin (21.1 or 42.2 micrograms/gm chow) or 6-MBOA (15.0 or 30.0 micrograms/gm). 4) Hamsters exposed to 6L:18D received drinking water containing melatonin (15.5 micrograms/ml) or 6-MBOA (11.0 micrograms/ml). Testis widths were determined at 2--3 week intervals, and after 66-73 days testes were removed and weighed. Melatonin significantly influenced testis size in each experiment, but treatment with 6-MBOA had no effect in any of these experimental paradigms, indicating that 6-MBOA does not act as a melatonin agonist in the hamster. However, these results indicate that the consumption of melatonin (and presumably melatonin agonists) could serve as an environmental stimulus for reproductive activity.

Geographical Ecology of Gerbilline Rodents in Sand Dune Habitats of Israel

In Israel, sand dune habitats of varying sizes occur along a rainfall gradient ranging from 30 to 650 m. In these sand dunes, nine species of granivorous rodents are found, eight of which belong to the family Gerbillidae. Rodent species were sampled during the four main seasons in eleven different locations covering the major sand dune habitats. Both species and their equivalent biomass were highly and significantly correlated with the mean annual rainfall. As the amount of rainfall increased, so did the number of species and their equivalent biomass. However, once a certain amount of rainfall was reached, an additional increase in rainfall was followed by a decrease in species number and biomass. Mean annual rainfall was similarly correlated with % annual cover, an index of the size of the seed crop on which the rodents feed. Number of rodent species was also significantly correlated with the area of the sand dune habitats. Analysis suggests that both rainfall and area are important in determining species number. Most of the patterns of community structure found in Israel are similar to those reported for the rodents that occur in the sand dunes of the desert of the western U.S.A.

The Number of Rodent Species in two Costa Rican Forests

The Number of Rodent Species in two Costa Rican Forests

Variations in the incorporation of thymidine into the DNA of some rodent species

1. 1. The ability of injected tritiated thymidine to serve as a precursor for DNA synthesis was tested in a number of rodent species. 2. 2. Radioautographs of tongue, duodenum and spleen showed good labeling for Mus musculus, Mesocricetus auratus, Glis glis, Eliomys quercinus and Scriurus carolinensis, inconstant labeling for Tamiasciurus hudsonicus and Tamias striatus, and no labeling for Marmota monax, Citellus tridecemlineatus and Citellus lateralis. 3. 3. Extraction of DNA from spleen and small intestine demonstrated a relative incorporation similar to the radioautographs. 4. 4. The urinary excretion patterns of M. musculus, M. auratus, C. tridecemlineatus and C. lateralis were similar with regards to volatile and non-volatile radioactivity; 8·5–18·9 per cent of the injected tritium was recovered as non-volatile radioactivity in the first 5 hr. 5. 5. In vitro incubatio of spleen cells with labeled thymidine demonstrated a relative incorporation in the DNA of the various species parallel to the in vivo findings. 6. 6. The urinary and in vitro findings suggest that the defect in thymidine incorporation found in several resides at the cellular level. 7. 7. The ability to incorporate thymidine showns some correlation with the phylogenetic relationship of the species tested, but no correlation with their ability to hibernate.

Genetic studies of the Syrian hamster. IV. Brown pigmentation.

A new mutant allele of the Syrian hamster is described. It is inherited as an autosomal recessive and is probably an homologue of the gene for brown pigment, a mutational step which is known to occur in a number of rodent species. In animals homozygous for the mutant allele, all the normal black eumelanin is changed to brown. The new coat colour engendered in this manner is described in detail. The brown allele has been tested for linkage against the genes cream and ruby-eye but the results were negative.