Microtus

About: Microtus is a research topic. Over the lifetime, 3074 publications have been published within this topic receiving 90728 citations.

Distance to Nearest Neighbor as a Measure of Spatial Relationships in Populations

Abstract: but since logging operations and the burning and reburning that followed this logging, aspen and white birch have taken over the role as dominants. Thirty-two islands and 5 mainland areas were chosen for the study. Three species of hibernators, Eutamias minimum, Tamias striatus and Zapus hudsonias were taken on the mainland with only the Zapus being found on the islands. All six of the non-hibernating species taken were found on the islands. These include Microtus pennsylvanicus, Synaptomys cooper, Clethrionomys gapperi, Peromyscus rncaniculatus, Blarina brevicauda and Sorex cinereus. The degree of occupancy changed from 4 out of 21 islands in 1950 to 21 of 24 islands in 1952. Along with this increase in the proportion of islands occupied there was an increase in the number of species found on most of the islands although the average number of species found on each occupied island did not change appreciably. This increase in islands occupied was correlated with an increase in the density of the mainland populations. The water seemed to be an efficient barrier to travel during the summer but the ice of winter became a highway for dispersal of the various nonhibernating species in the winter. Considerable difference was found in the vulnerability of the several species to trapping. The Perornyscus were readily caught. The Clethrionomys were not as easy to capture as the former but were still readily taken. The Microtus, however, posed a different problem. They were difficult to capture and on two islands of about 2.2 and 4 acres respectively we were not able to elim-inate them after 16 days of trapping on a 15-foot grid. The populations of small mammals fluctuate quite widely and the several populations appear to be somewhat independent of each other. The islands appeared to lag behind the mainland in the development of their populations.

Oxytocin receptor distribution reflects social organization in monogamous and polygamous voles.

Abstract: The neuropeptide oxytocin has been implicated in the mediation of several forms of affiliative behavior including parental care, grooming, and sex behavior. Here we demonstrate that species from the genus Microtus (voles) selected for differences in social affiliation show contrasting patterns of oxytocin receptor expression in brain. By in vitro receptor autoradiography with an iodinated oxytocin analogue, specific binding to brain oxytocin receptors was observed in both the monogamous prairie vole (Microtus ochrogaster) and the polygamous montane vole (Microtus montanus). In the prairie vole, oxytocin receptor density was highest in the prelimbic cortex, bed nucleus of the stria terminalis, nucleus accumbens, midline nuclei of the thalamus, and the lateral aspects of the amygdala. These brain areas showed little binding in the montane vole, in which oxytocin receptors were localized to the lateral septum, ventromedial nucleus of the hypothalamus, and cortical nucleus of the amygdala. Similar differences in brain oxytocin receptor distribution were observed in two additional species, the monogamous pine vole (Microtus pinetorum) and the polygamous meadow vole (Microtus pennsylvanicus). Receptor distributions for two other neurotransmitter systems implicated in the mediation of social behavior, benzodiazepines, and mu opioids did not show comparable species differences. Furthermore, in the montane vole, which shows little affiliative behavior except during the postpartum period, brain oxytocin receptor distribution changed within 24 hr of parturition, concurrent with the onset of maternal behavior. We suggest that variable expression of the oxytocin receptor in brain may be an important mechanism in evolution of species-typical differences in social bonding and affiliative behavior.

Gradients in density variations of small rodents: the importance of latitude and snow cover

Abstract: Microtine rodents are known to show extreme population variations (cycles) but non-cyclic populations have also been recognized during recent years. The cyclic populations have been widely thought to be regulated by intrinsic mechanisms. However, such predictions for cyclic populations are usually not applicable to non-cyclic ones and extrinsic factors may have to be included in any explanation.A hypothesis that the degree of fluctuations in small rodent numbers is related to the sustainable number of generalist predators was tested on mainly literature data by computing "indices of cyclicity" for local populations. These indices were related to latitude and snow cover (two measures) as these variables will affect the amount of alternative prey available for these generalists. Within Fennoscandia such indices for Clethrionomys glareolus and Microtus agrestis were clearly positively related to latitude and snow cover. The fraction of populations with summer declines in numbers, characterizing highly cyclic populations, increased in the same way. Cyclicity indices in Great Britain were similar to those in southern Fennoscandia, both areas being poor in snow, but were higher at the same latitudes in eastern Europe with more snow. Indices of density variations were generally low in North American Clethrionomys species and very variable in Microtus species.The gradients observed and differences between continents are interpreted as due to microtine-vegetation interactions in northern European areas poor in generalist predators but with important small mustelid predation, and to similar snowshoe hare-vegetation interactions in mainly Canada-Alaska, where small rodents may serve as alternative prey for numerically fluctuating hare predators, at least in the forests. Western European microtine populations, and probably many others, seem to be regulated by generalist predators.

Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene

Abstract: The molecular mechanisms underlying the evolution of complex behaviour are poorly understood. The mammalian genus Microtus provides an excellent model for investigating the evolution of social behaviour. Prairie voles (Microtus ochrogaster) exhibit a monogamous social structure in nature, whereas closely related meadow voles (Microtus pennsylvanicus) are solitary and polygamous. In male prairie voles, both vasopressin and dopamine act in the ventral forebrain to regulate selective affiliation between adult mates, known as pair bond formation, as assessed by partner preference in the laboratory. The vasopressin V1a receptor (V1aR) is expressed at higher levels in the ventral forebrain of monogamous than in promiscuous vole species, whereas dopamine receptor distribution is relatively conserved between species. Here we substantially increase partner preference formation in the socially promiscuous meadow vole by using viral vector V1aR gene transfer into the ventral forebrain. We show that a change in the expression of a single gene in the larger context of pre-existing genetic and neural circuits can profoundly alter social behaviour, providing a potential molecular mechanism for the rapid evolution of complex social behaviour.