Behavioural development of conspecific odour preferences in bank voles,Clethrionomys glareolus

Biological odours of conspecifics are known to have strong influences on behavioural interaction in bank voles Clethrionomys glareolus. This experiment tested two hypotheses. (1) Olfactory cues from familiar and unfamiliar mature opposite-sex conspecifics differ in their attractiveness to males and females, and their behavioural reactions change with age. (2) A genetically based mechanism is involved in female recognition of kin.In a two-choice preference test, prepubertal males and females were more attracted to familiar than to unfamiliar odours of opposite-sex conspecifics, as manifested by more time spent sniffing familiar voles. As the young reached sexual maturity they shifted their odour preferences. Mature males and females preferred the novel odour of unrelated opposite-sex conspecifics to that of relatives. The results of experiments testing the second hypothesis indicate that females use a genetically based mechanism to recognise their kin. Young and mature females were able to recognise the odour of their biological but socially unknown fathers, and showed the same pattern of behaviour as females in previous experiments.The possible biological functions of kin recognition in bank voles are discussed.     

Dermatophytes in a population of bank voles and woodmice

A population of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus) inhabiting an oak wood in Somerset was examined for dermatophytes at monthly intervals for 2 years. The marked animals were frequently retrapped, allowing a study of host fungus relationship over a period of time. Microsporum persicolor (Sabouraud) Guiart er Grigorakis and Trichophyton mentagrophytes (Robin) Blanchard were isolated from both animal species, but M. persicolor predominated in bank voles and T. mentagrophytes in wood mice. In their most favoured host, both dermatophyte species often persisted for several months, but in the less favoured host they were never isolated at more than one sampling. Males of both animal species were infected more often than females.The existing evidence for the geophilic nature of both fungi is reviewed and shown to be very weak, especially for M. persicolor.This is the first report from Great Britain of T. mentagrophytes infection of wood mice not in contact with human habitation.     

Meadow voles and prairie voles differ in the percentage of conspecific marks they over-mark

Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus, may deposit their own scent marks on top of those that were deposited previously by conspecifics. This phenomenon, known as over-marking appears to play a role in same-sex competition or mate attraction. The present study determines whether meadow and prairie voles avoid over-marking the scent marks of conspecifics, target the scent marks of conspecifics and over-mark them, or randomly over-mark the scent marks of conspecifics. The data show that meadow and prairie voles adjust the number and location of scent marks that they deposit in areas marked previously by particular conspecifics. Male and female meadow and prairie voles target the scent marks of opposite-sex conspecifics and over-mark them. Female meadow and prairie voles also target the scent marks of female conspecifics. In contrast, male meadow and prairie voles over-mark the scent marks of male conspecifics in a random manner. By differentially over-marking the scent marks of conspecifics, voles may be able to communicate particular information to a variety of conspecifics.     

Reproduction and population density affect humoral immunity in bank voles under field experimental conditions

Density dependence is a common feature in the dynamics of animal populations. Availability of food resources critical to immunity is likely to be one of the mechanisms mediating the effect of population density on individual fitness. The ability to mount an immune response to an antigen is also affected by levels of immunosuppressive hormones associated with reproduction or mediating the response to ecological and social stress. We assessed variation in condition and intensity of humoral immune response to a T-cell-dependent antigen in bank voles (Clethrionomys glareolus) by experimentally altering population density before immunisation. Consistent with our prediction, males had lower humoral immunocompetence in the breeding than in the non-breeding season. Contrary to our expectation, males did not show enhanced immunocompetence and females showed depressed humoral immune response under experimentally lowered population density. Variation of immune response in relation to population density depended on sex, with females but not males showing lower immune response under experimentally reduced density. We conclude that humoral immunity of bank voles was affected by reproduction and social environment rather than by population density. Received: 2 November 1999 / Accepted: 22 March 2000     

Differential sensitivity to conspecific and allospecific cues in chimpanzees and humans: a comparative eye-tracking study

Previous studies have shown that a variety of animals including humans are sensitive to social cues from others and shift their attention to the same objects attended to by others. However, little is known about how animals process conspecifics'' and another species'' actions, although primates recognize conspecific faces better than those of another species. In this study, using unrestrained eye-tracking techniques, we first demonstrated that conspecific social cues modulated looking behaviours of chimpanzees more than human cues, whereas human observers were equally sensitive to both species. Additionally, first pass gaze duration at the face indicates that chimpanzees looked at the chimpanzees'' face longer than the human face, suggesting that chimpanzees might extract more referential information from a conspecific face. These results also imply that a unique ability for extracting referential information from a variety of social objects has emerged during human evolution.     

The effects of predator presence and shoal size on foraging in bluntnose minnows,Pimephales notatus

Synopsis Shoals of 3, 5, 7, 10, 15, and 20 bluntnose minnows,Pimephales notatus, were allowed to forage in the absence and presence of a fish predator, which was separated from the shoal by a clear plexiglass partition. A typical dilution effect was observed in that individual fish in larger shoals were approached less frequently by the predator. In the absence of a predator, foraging latency decreased significantly and the rate of foraging increased with increasing shoal size. Foraging latency for each shoal size tended to increase in the presence of a predator and foraging rate decreased, significantly for shoals of 7, 15, and 20 fish. Members of larger shoals were safer and enjoyed a greater level of food consumption, perhaps due to decreased individual vigilance for predators and social facilitation. However, foraging effort decreased when a predator was present, as more time was allocated to predator avoidance.     

Primer effects by conspecific odors in house mice: a new perspective in the study of primer effects on reproductive activities

Half a century has passed since the first report of the influence of odors on mice. Odors are known to influence behavior (signaling effect) and affect the physiology (primer effect) of mice. This review focuses on summarizing the primer effects found so far in female and male mice. Odors from conspecifics of the opposite sex had the tendency to enhance reproductive activities, whereas odors from conspecifics of the same sex diminish them. Only 2,5-dimethylpyrazine, one of the odor components identified in group-housed females, has been reported to have a suppressive influence on both males and females by lowering reproductive activities. Studies showed progress from the discovery of phenomena to the identification of odor components that cause such changes in reproductive organs and related neuroendocrinological changes. Compared to studies on the mechanisms of primer effects in females, the mechanisms in males are not yet clarified, and detailed studies on effects on the reproductive organs are still in primitive stages especially for males. Hypotheses on the influence of changes in the concentration of testosterone, estrogen, and prolactin on spermatogenesis and sperm maturation after exposure to odors are discussed.     

Reproductive effort of female bank voles in a risky environment

In cyclically fluctuating vole populations, strong intraspecific competition and intense predation simultaneously or separately increase the costs of reproduction and so may set the framework for the optimal breeding tactic of voles. In a factorial experiment, we manipulated two factors in the breeding environment of bank vole (Clethrionomys glareolus) pairs, each with two treatment levels: no predation risk or high risk of specialist predators and low or high density of voles. In the manipulation, we used odours of conspecific voles and/or mustelid predators. Both over-wintered and young, summer-born, wild-caught bank vole females and males in breeding condition were used. Each female—male pair of voles was placed in a cage and the cages were distributed in large outdoor enclosures. All animals were fed ad libitum. Under predation risk, both old and young females suppressed breeding significantly. The density of conspecific voles did not affect overall breeding. However, there was some evidence that population density stimulated breeding of old females but suppressed breeding of young ones. Both risk factors appeared to increase litter sizes of those individuals who decided to breed. Our results indicate that the risk of predation may be an important factor determining reproductive tactics of bank vole females. In risky environments, females seemed to choose between two totally opposite tactics: they suppressed breeding, which may increase their own survival to the next breeding event, or they continued to breed in spite of expected high survival costs. Females seemed to compensate the latter costs with a higher effort to the current and probably the last reproduction.     

Road crossing in bank voles and yellow-necked mice

Roads and highways represent one of the most important anthropogenic impacts on natural areas and contribute to habitat fragmentation, because they are linear features that can inhibit animal movement, thereby causing barrier effects subdividing the populations adjacent to the roads. The paper examines to what extent a narrow (2-lane) and a wide (4-lane) highways represent barriers for two small mammal species: bank volesClethrionomys glareolus Schreber, 1780 and yellow-necked miceApodemus flavicollis Melchior, 1834, and whether displaced rodents are able to return across roads of different widths. The study was performed at four sites in the Czech Republic. The capture-mark-recapture method was used to determine crossing rates. At two sites, the animals captured close to the road were transferred to the other side and released, to compare return movements across the roads with the movements made by the non-transferred animals. We found that the narrow highway did not prevent movement of neither of the species, although voles crossed only after they had been transferred. Wide highways, on the other hand, completely prevened crossing of both species. While the narrow highways acted at individuals level, the wide highways affected the population subvision.     

Tubes and foraging behavior in larval Chironomidae: implications for predator avoidance

Summary In laboratory experiments, I studied differential susceptibility of four co-occurring species of chironomids to a predatory damselfly. The chironomids differed in foraging behavior and could be ranked according to the amount of time they spent outside of their tubes. In choice experiments, the predator consistently selected the prey which spent more time out of the tube, and time out of tube was a significant predictor of the predation rate coefficient. Electivity indices, calculated from field samples and diet analyses of the predator, supported the laboratory results. The data suggest that exposure to predators in a heterogeneous prey community is largely determined by tubedwelling behavior.     

Impact of Puumala virus infection on maturation and survival in bank voles: a capture-mark-recapture analysis

Many zoonotic diseases are caused by rodent-borne viruses. Major fluctuations in the transmission of these viruses have been related to large changes in reservoir host population numbers due to external factors. However, the impact of the pathogen itself on the demography of its reservoir host is often overlooked. We investigated the impact of Puumala virus (PUUV) on survival and reproductive maturation probability of its reservoir host, the bank vole (Myodes glareolus). Three years (2004-06) of data from nine independent sites in southern Belgium were collected and analyzed with a capture-mark-recapture (CMR) method that includes statistical correction for the variation in capture probability of voles. A multistate model based on four states of reproductive activity and PUUV immunoglobulin G (IgG) antibody status was used to estimate survival and probability of transition from one reproductive or infection state to another. Although survival estimates for reproductively active voles were similar between infected and noninfected individuals, PUUV infection in reproductively inactive voles decreased mean monthly survival by 14%. PUUV infection was associated with a threefold increase in the probability of reproductive maturation in bank voles. Moreover, the probability of PUUV IgG seroconversion was three times higher for reproductively active voles compared to reproductively inactive voles. Our model indicates that PUUV infection may alter bank vole population dynamics by affecting both survival and maturation in its host. Additional studies, using CMR methodology with shorter time intervals between trapping sessions and possibly a longer duration, are needed to confirm these findings.     

A functional response model of a predator population foraging in a patchy habitat

1. Functional response models (e.g. Holling's disc equation) that do not take the spatial distributions of prey and predators into account are likely to produce biased estimates of predation rates. 2. To investigate the consequences of ignoring prey distribution and predator aggregation, a general analytical model of a predator population occupying a patchy environment with a single species of prey is developed. 3. The model includes the density and the spatial distribution of the prey population, the aggregative response of the predators and their mutual interference. 4. The model provides explicit solutions to a number of scenarios that can be independently combined: the prey has an even, random or clumped distribution, and the predators show a convex, sigmoid, linear or no aggregative response. 5. The model is parameterized with data from an acarine predator-prey system consisting of Phytoseiulus persimis and Tetranychus urticae inhabiting greenhouse cucumbers. 6. The model fits empirical data quite well and much better than if prey and predators were assumed to be evenly distributed among patches, or if the predators were distributed independently of the prey. 7. The analyses show that if the predators do not show an aggregative response it will always be an advantage to the prey to adopt a patchy distribution. On the other hand, if the predators are capable of responding to the distribution of prey, then it will be an advantage to the prey to be evenly distributed when its density is low and switch to a more patchy distribution when its density increases. The effect of mutual interference is negligible unless predator density is very high. 8. The model shows that prey patchiness and predator aggregation in combination can change the functional response at the population level from type II to type III, indicating that these factors may contribute to stabilization of predator-prey dynamics.     

Evolution of predator avoidance in a Daphnia population: evidence from the egg bank

Dormant propagule pools (egg banks) of zooplankton populations that accumulate in sediments provide biological archives of past conditions and enable the investigation of evolutionary changes in populations over relatively long periods of time (many decades). This study examined the egg bank of a Daphnia pulicaria population in a lake that has been stocked annually with rainbow trout (a zooplanktivore) since 1961. Resting eggs from sediments from the 1920s to 2001 (determined by ²¹⁰Pb dating) were hatched and established as isofemale clonal lines. The phototactic behavior (a proxy for vertical migration behavior) of clones was assessed in the presence and absence of fish kairomones to evaluate the hypothesis that the heavy and consistent level of predation imposed by the stocked trout would have selected for clones that are more negatively phototactic. In addition, exposure to kairomones was expected to induce stronger negative phototaxis for all clones relative to control conditions. The behavior of clones derived from resting eggs from the trout era (after 1961) was significantly more negatively phototactic than it was for pre-trout era clones. Kairomone exposure induced a more negative phototactic response in clones from both eras, but the response was much greater for the pre-trout era clones. These results suggest that the consistently high level of predation by trout over several decades has selected for a conservative (less plastic) vertical migration strategy in which Daphnia maintain a deep daytime distribution with or without the presence of chemical cues from fish predators.     

Effects of conspecific and heterospecific residents on patterns of immigration in two species of voles

Studies with birds have shown that presence and density of resident conspecifics and heterospecifics can influence patterns of habitat selection. There have been few studies on the effects of social cues on rates of immigration in mammals. We report results from a long-term live trapping study of immigration in two species of voles, Microtus ochrogaster Wagner, 1842 and Microtus pennsylvanicus Ord, 1815, in bluegrass habitat in east-central Illinois, USA. We compare immigration into control sites from which no individuals of either species were removed with immigration into experimental sites from which either conspecifics or heterospecifics were removed. We focus on characteristics of immigrants and rates of immigration in relation to density in destination habitats. Within each species, immigrants into control and removal sites were similar with respect to body mass and reproductive condition, indicating no major differences in the physical condition of immigrants into sites with established populations and sites without established populations. For both species, density of conspecifics at a site positively influenced rate of immigration at that site. Density of heterospecifics at destination sites did not significantly influence rate of immigration for either species. These results suggest that site selection by dispersing M. ochrogaster and M. pennsylvanicus is characterized by conspecific attraction.