Seasonal changes in white and brown adipose tissues in Clethrionomys gapperi (red-backed vole) and in Microtus pennsylvanicus (meadow vole)

The seasonality of reproduction in photoperiod responsive and nonresponsive northern red-backed voles (Myodes rutilus) in Alaska

High-latitude arvicoline rodents usually reproduce in warmer months, but winter breeding has been documented in several species, including the northern red-backed vole ( Myodes rutilus (Pallas, 1779) Wilson and Reader, 2005; formerly Clethrionomys rutilus (Pallas, 1779)). We tested whether the reproductive condition of the species is linked to changes in environmental parameters or its body condition, and we tested the frequencies at which different reproductive phenotypes are exhibited under field and laboratory conditions. Free-living voles in south-central Alaska reached peak reproductive organ masses in spring (females) and early summer (males). Between-subject comparisons showed an effect of body mass, photoperiod, percent fat, temperature, and snow depth on reproductive organ masses, depending on the sex and breeding period (p < 0.05). One instance of late-summer photoperiod nonresponsiveness was observed, but we detected no winter breeding. Captive male voles given food ad libitum and housed at room temperature exhibited strong phenotypic variation in testis mass in response to short photoperiods. The percentage of nonresponders was 28.2% and was within the known range of nonresponsiveness for lower latitude species (20%–40%). Thus, photoperiod nonresponsive morphs are conserved in at least one arctic and subarctic species at frequencies comparable to lower latitude voles despite no observance of winter breeding in the field. Voles exhibit reproductive elasticity and may breed in winter if environmental conditions enable them.

Analysis of expressed sequence tags from subtracted and unsubtracted Ctenocephalides felis hindgut and Malpighian tubule cDNA libraries

Insect hindgut and Malpighian tubule (HMT) tissues regulate the contents of the haemolymph through the excretion of waste products and the specific reabsorption of nutrients. As such, they perform a role that is essential for survival and may contain molecular targets for insect control strategies. In order to discover genes expressed in the HMT tissues of the cat flea, Ctenocephalides felis, expressed sequence tags (ESTs) were generated from an unsubtracted HMT cDNA library and from a subtracted HMT cDNA library that had been enriched for HMT-specific cDNAs. A total of 4844 ESTs were analysed from both libraries: 3657 from the subtracted library and 1187 from the unsubtracted library. Of the 1418 distinct ESTs identified from both libraries, 953 had significant similarity to other sequences reported in the GenBank database. A comparison of the results from the two libraries confirmed that the percentages of genes likely to be involved with metabolism, cell structure, and digestion were reduced by the subtraction procedure, whereas genes likely to be involved with ion transport were enriched. Analysis of the prevalence of three individual cDNAs in each library revealed that the actin cDNA was reduced in the subtracted library whereas the cDNAs encoding allantoinase and a peritrophin-like protein were greatly enriched in the subtracted library. Northern blot analysis demonstrated that the actin cDNA was expressed in both the HMT and carcass tissues, whereas the allantoinase and peritrophin-like cDNAs were detected exclusively in the HMT tissues. In total, 97 distinct ESTs that appear to encode proteins involved with ion transport were analysed. Some of these proteins may be directly involved with diuresis or the specific reabsorption of salts and nutrients, and thus may be potential molecular targets for flea control strategies.

The winter immunoenhancement hypothesis: associations among immunity, density, and survival in prairie vole (Microtus ochrogaster) populations

Seasonal variations in photoperiod, temperature, and population density have been shown to modulate immune responsiveness of animals in laboratory studies. To examine these associations under natural conditions, we monitored 3 populations of prairie voles (Microtus ochrogaster) for temporal variations in selected immunological parameters, population density, and survival rate from winter 1996 to spring 1997. Spontaneous and cytokine-stimulated T-cell proliferative responsiveness of prairie voles peaked in winter and declined in spring. Relative organ mass, hemolytic-complement activity, and in vivo hypersensitivity responses varied temporally but showed no clear seasonal trend. The population density and survival rate of all 3 prairie vole populations varied temporally and correlated with measures of immunity. Multiple regression analysis indicated that the model containing relative spleen mass, cytokine-stimulated T-cell proliferation, and in vivo hypersensitivity explained a significant amount of variability in population density, while cytokine-stimulated T-cell proliferation and relative thymus mass explained a significant amount of variability in survival rate. The results suggest that seasonal environmental changes can enhance immune responsiveness of a host and may counteract the immunoenhancing effects of photoperiod in wild populations of prairie voles. Our results also suggest that there is an association between immune function and demography in wild populations.

Seasonal variation in body composition and gut capacity of the prairie vole (Microtus ochrogaster)

Prairie voles (Microtus ochrogaster) were trapped during different seasons in order to examine simultaneous variation in body composition and gut capacity. Voles in reproductive condition were trapped in May, August, and November but not in February. Body masses of adult voles were lowest during February 1994. Adult males showed no seasonal variation in absolute lipid mass but did exhibit variation in relative fat content (percent body fat), with the highest values found in February 1994. Both absolute lipid mass and relative fat content of adult females varied with month of capture and were higher in February of both 1994 and 1995. Juvenile voles showed no variation in body composition between seasons and had fat levels similar to those of adult voles in the breeding months. Wet mass of the gastrointestinal tract varied with season of capture for both adult males and females, but no distinct pattern was evident. Mass of gut contents varied between trapping periods for adult males, but there were no seasonal differences in the gut contents of adult females or juveniles. The average mass of gut contents was higher than previously reported for field-caught prairie voles; this difference is likely due to the use of snap traps versus live traps.

Anemia at the onset of winter in the meadow vole (Microtus pennsylvanicus)

1. From 1981 to 1986, 6120 meadow voles (Microtus pennsylvanicus) were sampled for hematological indices in southeastern Manitoba, Canada. This survey revealed the sporadic occurrence of anemia in early winter at mean temperatures below about -5 degrees C. 2. Anemia was associated with leukocytosis and circulating normoblasts, suggesting a sudden, large blood loss. Individuals became anemic quickly, with no obvious predisposing factors. 3. Attempts were made to induce anemia by exposing voles in traps to various temperatures. Temperatures characteristic of most trapping sessions failed to induce anemia in both wild and laboratory-born voles. 4. Short-term exposure to more extreme temperatures (-20 to -30 degrees C) induced anemia. Voles lost blood through erosions of the epithelium of the glandular stomach, and developed other pathological lesions characteristic of hypothermia. 5. Although there was a strong association between cold weather and anemia, we could find no clear relationship between winter survival and winter weather. However, in 1984, extraordinarily cold temperatures were associated with anemia and a subsequent population decline. These events suggest a threshold mean daily temperature of about -15 degrees C, below which vole survival is grossly affected. 6. Deteriorating protein levels and energy reserves of small mammals in winter may make them particularly susceptible to cold stress. Hence, sporadic bouts of sustained cold may be responsible for some of the enigmatic winter declines seen in northern small mammals.

Seasonal acclimation of bank voles and wood mice: nonshivering thermogenesis and thermogenic properties of brown adipose tissue mitochondria

Seasonal acclimation of nonshivering thermogenesis and brown adipose tissue was studied in wild bank voles (Clethrionomys glareolus), yellow necked field mice and wood mice (Apodemus flavicollis, A. sylvaticus). Both, voles and mice increased their capacity for nonshivering thermogenesis during winter. Thermogenic properties of brown fat (cytochrome c oxidase activity, mitochondrial protein content, GDP-binding of brown fat mitochondria) showed similar changes during seasonal acclimation; Clethrionomys and Apodemus spp. both showed lowest thermogenic properties in the summer during August, a rapid increase during fall, and highest levels of thermogenic activity in the winter months. With regard to changes in body weight and brown fat mass these species show different strategies for seasonal acclimation. In Clethrionomys a reduction of body mass in the winter was found, both in the wild population as well as in individual animals housed in the laboratory. A. flavicollis showed a reduction of body weight during fall, whereas A. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in the Apodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas in Clethrionomys brown fat mass and cellularity remained seasonally constant. These species live in the same habitat and were trapped in the same area. It is concluded that seasonal improvements of in vivo and in vitro thermogenesis are very similar in these species, although the physiological basis for this improvement is different in Clethrionomys and Apodemus.