Jean-Marie Bergeron

Repeatability of daily field metabolic rate in female Meadow Voles (Microtus pennsylvanicus)

1. Repeated measurements of daily field metabolic rate (FMR) were made on 11 Meadow Voles (Microtus pennsylvanicus Ord.) by means of the doubly labelled water technique. The objective was to quantify the individual consistency of FMR by calculating the repeatability of successive measures on the same individuals. One more general goal was to test whether FMRs are sufficiently repeatable to be convenient for field studies of natural selection. 2. Voles were all non-reproductive females, 5-7-months old. They were maintained individually in outdoor enclosures 25m 2 and were injected 1-3 times with doubly labelled water. Two to six measures of daily FMR were thus obtained per individual (x = 4.09, SD = 1.51, n = 11) over a period of 42 days in July and August 1994. 3. Body mass and rate of change in body mass accounted for 31.6% of the observed variation in FMR; ground-temperature variations had no significant effect on FMR, probably owing to the small range of temperatures experienced by voles. 4. Repeatability of mass-corrected log 10 FMR measurements was low (r=0.261). This low repeatability was very consistent with the results of a previous study on consistency of mass-specific daily energy expenditures of caged pouched mice. 5. A partition of the total variance observed in mass-corrected FMR showed that 63.0% of the variance originated from differences within individuals, 27.6% from differences among individuals, and 9.4% from measurement error. FMR was not consistently higher or lower on the first or second day of measurement, indicating no clear effect of handling stress. 6. A practical implication of these results is that single measurements of daily field metabolic rates are not necessarily a good predictor of the average 24 h energy budget for a given individual. On a more theoretical basis, these results indicate that, although the ability of an animal to manage its energy economics may largely determine its selective value, daily FMR seems to be a poor candidate variable to relate this ability to individual fitness in experimental studies. 7. We suggest that future studies of repeatability of FMR should concentrate on energetically constraining periods. This would allow further evaluation of the potential role of interindividual differences in FMR as a tool for understanding evolutionary pathways that shaped energy economics of animals.

Defining “high quality” food resources of herbivores: the case for meadow voles (Microtus pennsylvanicus)

SummaryFood availability, food utilization patterns and levels of some nutritional factors in plants were studied in 1984–85 in an old-field community supporting low to moderate densities of meadow voles (Microtus pennsylvanicus). Food choice and preference indices were positively related to levels of proteins, and negatively related to levels of total phenolics and ADL fibers in plants. High quality resources for voles were resources that had the highest amount of proteins, and the lowest level of total phenolics and ADL fibers among available plant species. There were only two plants species among the available ones that possessed these characteristics, Festuca rubra and Vicia cracca and they represented 25 to 50% of the available biomass during summer. Vole densities of up to 64 animals/ha were therefore not limited by the availability of high quality resources. Fecal analyses performed on 267 animals in 1984 and 269 voles in 1985 showed that all voles ate high quality resources. Meadow voles appear to choose foods with high protein content and low levels of digestion inhibitors, and not on the basis of caloric content or availability. These observations contradict predictions arising from current antiherbivore hypotheses and lead us to reconsider these models in light of this new evidence.

Multiple paternity in meadow voles (Microtus pennsylvanicus): investigating the role of the female

Abstract Multiple paternity in single litters conceived in the wild was recently demonstrated in meadow voles (Microtuspennsylvanicus). In this study, we used an experimental approach (males tethered and females allowed to mate freely with one or several males) to investigate the role of female meadow voles in multiple paternity. We found that among 29 (of 39) females that copulated during our experiment, 79.3% chose to mate with more than one male. Female behavior in meadow voles thus clearly promotes multiple paternity and their role is an active one. Some of the hypotheses explaining promiscuity in meadow voles should be reconsidered in light of this result. We do not know the primary determinant of female mate choice, but male body mass played a secondary role in driving female preferences. The partial dependence between male body mass and female choice, coupled with the active role played by females, indicates that intersexual selection has the potential for reinforcing the effects of intrasexual selection (male-male dominance relationships) in this species. Finally, we demonstrate that the time period over which tests are conducted is an important part of the design of experiments aimed at understanding the role of females in multiple paternity.

Metabolic Costs Associated with the Ingestion of Plant Phenolics by Microtus pennsylvanicus

We measured the basal metabolic rate of meadow voles, Microtus pennsylvanicus , before and after incorporating the phenol gallic acid (6% by dry mass) into the diet. After phenolics were added, basal metabolic rates increased by 13.6–22.6%. This indicates that there are measurable metabolic costs associated with feeding on plants that contain phenolics. These costs may be associated with detoxification and tissue repair, but their cause is not known.

Effect of carrying a radiocollar on expenditure of energy by meadow voles

We compared the daily expenditure of energy of meadow voles ( Microtus pennsylvanicus ) with and without dummy radiocollars. Daily expenditure of energy was estimated by doubly labelled water, while voles were kept in large outdoor cages. Carrying a radiocollar (6.7–9.0% of body mass) had no effect on daily expenditure of energy. Metabolism of caged animals was not inferior to that of free-ranging ones, suggesting that caging did not reduce locomotory costs and that radiocollars do not influence energy budgets of voles in natural conditions. Subsequently, we remove a potential argument against the use of telemetry on mammals of small size. We also validate the simultaneous use of radiotelemetry and doubly labelled water in small running mammals, which should offer new opportunities to investigate ecological energetics of these species.

Solitude versus gregariousness : do physical benefits drive the choice in overwintering meadow voles ?

Winter group formation has been described for many small rodent species living in temperate environments. Physical benefits (e.g. energy and water conservation) of huddling are generally considered to be the ultimate cause of these aggregations. We manipulated group size of meadow voles (1 versus 4 individuals) in a field experiment involving 40 individuals (5 replicates, each including 4 solitary-living and 4 group-living individuals) to test the validity of the physical benefits hypothesis. Energy expenditures and water flux were measured using the doubly labelled water method. Group size had no effect on field metabolic rate, water turnover, body mass changes, body composition, and survival. The role of physical benefits as the driving force behind winter aggregations should thus be reevaluated. Future studies should concentrate on specific time periods characterized by extreme climatic conditions. Alternative benefits of aggregations, such as decreased predation risk or social transmission of information, should also be considered.

Patterns of resource use, food quality, and health status of voles ( Microtus pennsylvanicus ) trapped from fluctuating populations

SummaryRecent studies suggest that diet quality is responsible for differential survivorship of vole cohorts (Boonstra and Boag 1987) and spacing behavior of females (Ims 1987). These phenomena have been related either to a lack of or a deterioration in the quality of the preferred food. To test this hypothesis, we compared foods habits, food quality and health status of meadow voles (Microtus pennsylvanicus) from high and low population density phases. In this study, seven plant species represented the main food items used on a regular basis and biomass values of preferred species decreased with browsing pressure. In addition, food quality of the main dietary items changed between phases forcing females to adjust their feeding strategy accordingly. Health of voles changed also opening the way to speculations on competition for high quality food resources and survivorship.

Effects of Food Quality on Feeding Patterns of Meadow Voles (Microtus pennsylvanicus) along a Community Gradient

Diet selectivity by meadow voles ( Microtus pennyslvanicus ) was examined relative to nutritional characteristics of plants in 5-, 20-, and 30-year-old meadows. Food selection was correlated negatively with lignin content of plants in 5-year-old meadows, positively with the ratio of protein to acid-detergent lignin in 5- and 20-year-old habitats, and positively with protein levels and negatively with total phenolics or condensed tannins of plants in 30-year-old meadows. Total content of phenolics in plants increased consistently with age of meadows, reflecting an apparent general decline in overall nutritive quality of plants from early to late successional stages.

Differences in nutritional quality between herbaceous plants and bark of conifers as winter food for the vole Microtus pennsylvanicus

1. Meadow voles (Microtus pennsylvanicus) are known to inflict severe winter damage on young tree plantations by gnawing the bark. This is often attributed to a lack of quality and quantity of food supply, although no direct evidence has ever been found. A first step in this direction was initiated by comparing the quality of food supply between herbaceous plants and bark of coniferous species during the winter periods of 1987-88 and 1988-89. 2. Food quality was assessed by measuring the content of protein, total nonstructural carbohydrates (TNC) and total phenolics using standard methods. 3. The nutritional value of herbaceous plants was overall much greater than that of the bark of conifers for both winters analysed. Ratios involving protein/phenolics and TNC/phenolics were up to 50 times higher in herbaceous species than bark of conifers. 4. Nutritional components from herbaceous plants did not vary much between winter months unlike the bark tissues of conifers. 5. These results indicate that voles do not attack conifers because of their high nutritional quality suggesting that other factors such as a lack of a good quality alternative food supply (herbaceous plants) are involved.

Abundance and developmental stability of Pterostichus melanarius (Coleoptera: Carabidae) in organic and integrated pest management orchards of Québec, Canada

Abstract This study evaluated the agricultural impacts of organic and integrated pest management (IPM) orchards in Québec, Canada on the carabids Pterostichus melanarius Illiger (Coleoptera, Carabidae), with two biomonitors, population density and fluctuating asymmetry (FA) of morphologic and meristic characters. The carabids were trapped between May and August 1999 and 2000 in 20 pitfall traps on four organically certified orchards and five IPM farmlands located in two farming communities 100 km apart. Numbers of P. melanarius and total trap catch were assessed for each year. We measured the length of two segments of the right and left antennae, the length of first tarsae, and the number of tibiae spines on the mesothoracic leg of 50–100 individuals per site/yr. These measurements were used to calculate two fluctuating asymmetry indices to evaluate individual developmental stability. No differences in fluctuating asymmetry were found between organic and IPM orchards although total catch of P. melanarius was higher in IPM orchards in 1999. The use of fluctuating asymmetry analysis in these fields seem inadequate to assess the impact of pesticides. Density analysis give a slightly response in the opposite of the predictions because IPM orchards seem to be a more adequate habitat for this carabid species. There is a need for evaluating the impacts of natural products used in the organic cultures.