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PubMedDate not supplied

Social status does not affect resting metabolic rate in wintering dark-eyed junco (Junco hyemalis).

Studies of wintering birds have demonstrated a correlation between social rank and energy expenditures. It is assumed that dominance is energetically costly because of increased activity, possibly caused by elevated androgen levels. As winter acclimatization leads to an increase in metabolic rate, maintaining dominance status in a cold climate can be a substantial challenge. We measured resting metabolic rates in dominant and subordinate dark-eyed juncos (Junco hyemalis) living in small groups in a controlled winter environment. We found no significant effect of social rank when controlling for body size. It has been shown previously that high testosterone levels during the nonbreeding season can lead to higher body conductance, fat loss, and higher nocturnal body temperature. A hypothesis explaining our result is that for juncos it is preferable to maintain low androgen levels during winter and to maintain social rank using a mechanism other than higher agonistic activity.

Agonistic Behavior↗
PubMed2004

Optimal body size and energy expenditure during winter: why are voles smaller in declining populations?

Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation.

Animals↗
PubMedDate not supplied

Body temperatures and activity patterns of Tasmanian devils (Sarcophilus harrisii) and eastern quolls (Dasyurus viverrinus) through a subalpine winter.

During a field study of carnivorous dasyurid marsupials in subalpine Tasmania, the trapping success for Tasmanian devils (Sarcophilus harrisii), but not for spotted-tailed quolls (Dasyurus maculatus) or eastern quolls (Dasyurus viverrinus), was significantly lower when winter weather conditions turned to sleet or snow or when deep snow lay on the ground. This field study was instigated to determine if devils and eastern quolls spend more time in burrows in severe weather conditions and if they enter torpor. Torpor is known to occur in eutherian mammals as large as devils and in a similar-sized congeneric marsupial, the western quoll (Dasyurus geoffroyi). Using radiotelemetry, body temperatures of Tasmanian devils and eastern quolls ranging freely in their natural habitat were monitored throughout winter. Neither species was observed in torpor, even under prolonged severe weather conditions, and the number of hours spent active not did differ between summer and winter or between moderate and severe winter weather conditions. Body temperatures averaged 36.5 degrees C (SD = 0.079, range of 33.5 degrees-38.6 degrees C) for the three male eastern quolls and 35.7 degrees C (SD = 0.575, range of 31.3 degrees-37.5 degrees C) for the four (male and female) devils. A diel cycle in body temperature occurred in both species; temperatures rose each evening when animals became active, remained high throughout the night despite ambient temperatures falling to the diel minima, and were lower during the day when the individuals were inactive in dens. The amplitude of this cycle was greater in eastern quolls (1.1 degrees C, SD = 0.142) than in devils (0.6 degree C, SD = 0.252).

Analysis of Variance↗
PubMed1995

Life-style factors associated with winter serum 25-hydroxyvitamin D levels in elderly adults.

A cross-sectional survey of community-dwelling elderly volunteers (104 women, 87 men, mean age 70 years) was carried out in winter to determine whether cardiovascular and other potentially modifiable lifestyle factors were associated with serum levels of 25-hydroxyvitamin D during this period. Mean winter levels of serum 25-hydroxyvitamin D were higher in men than in women (14.2 vs. 12.2 ng/ml, p = 0.021), higher in those who used margarine daily compared with less often (14.4 vs. 11.9 ng/ml, p = 0.005), and higher in those who holidayed overseas in the last 6 months at a lower latitude than in Great Britain or Germany (14.9 vs. 12.4 ng/ml, p = 0.044), after controlling for other confounders. Serum 25-hydroxyvitamin D levels were not related to the number of hours spent outdoors during the previous month (r = 0.04, p > 0.05). When participants were classified by tertile of low-density lipoprotein (LDL) cholesterol, mean serum 25-hydroxyvitamin D was raised in the highest (14.3 ng/ml, p = 0.011) and middle (13.3 ng/ml, p = 0.15) tertiles compared with the lowest tertile (11.9 ng/ml), after controlling for other confounders. All other cardiovascular risk factors, including total- and HDL-cholesterol, blood pressure, BMI, smoking and leisure physical activity, were unrelated to serum vitamin D. These results suggest that body vitamin D levels in elderly people during winter are related to diet and overseas holidays within the last 6 months, but not to UK winter sun exposure, nor to the major cardiovascular risk factors apart from LDL cholesterol.

Aged↗
PubMed1993

Elevated ornithine decarboxylase activity, polyamines and cell proliferation in neoplastic and vacuolated liver cells of winter flounder (Pleuronectes americanus)

Liver neoplasms, including hepatocellular and cholangiocellular tumors, commonly occur in winter flounder (Pleuronectes americanus) caught from some chemically contaminated areas such as Boston Harbor. Hydropically vacuolated cells, very often associated with neoplasia in winter flounder liver, appear to represent the first cellular abnormality in animals that later develop frank neoplasms. The proliferative capacity of hydropically vacuolated cells was studied by analyzing both ornithine decarboxylase (ODC) activity and bromodeoxyuridine (BrdU) labeling indices. Liver of winter flounder with vacuolated cellular lesions had ODC activity more than 5- to 12-fold greater than that in liver that lacked such vacuolation, whether caught from Boston Harbor or Georges Bank. Large focal areas of hydropically vacuolated cells dissected from severely affected livers had ODC activity as high or higher than surrounding parenchymal tissue. Significant elevations in hepatic polyamine levels and ratios of putrescine/spermidine were also present in all Boston Harbor animals studied, especially those exhibiting vacuolated cellular lesions, as compared to Georges Bank fish. BrdU labeling techniques indicate that hydropically vacuolated cells, along with perivacuolar small basophilic cells and neoplastic cholangiocytes, appear to have the capacity to synthesize DNA and undergo mitosis. The frequent association of hydropically vacuolated cells with hepatic neoplasia, along with high ODC activity and DNA synthesis capability, suggest that the vacuolated cells and/or perivacuolar basophilic cells may be integral to the development of some neoplastic phenotypes in winter flounder liver.

Animals↗
PubMed2026

Museum genomics links MC1R alleles to adaptive winter coat color polymorphism in the long-tailed weasel.

Understanding the architecture of biological adaptations is a major endeavor of evolutionary biology. Using Natural History collections, we study the genetic basis and evolution of white/brown winter coat color variation in the long-tailed weasel (Neogale frenata), a crucial phenological adaptation for camouflage in habitats with seasonal snow. We produced whole-genome sequencing data for museum specimens, along two winter color morph transition areas in North America, at the West and East coasts. Genome-wide association scans identified a single genomic region linked to color variation polymorphism with approximately 300 kb and 200 kb in the West and East regions, respectively, which included the pigmentation gene MC1R. We identified three MC1R alleles, two of which with deletions of nine or eight amino acids, alternatively associated with the winter brown morphs in the West and East, respectively. These deletions affect the second transmembrane domain, and in one case also the first extracellular loop, which in silico analyses predicted to impact the protein's function. Our findings show alternative intraspecific evolutionary solutions for environmental adaptation in long-tailed weasels, building on the evidence that major genes of the melanin production pathway are hotspots for recurrent and independent evolution of winter camouflage adaptation. This adaptive variation may be crucial to anchor adaptive responses facing future environmental change.

Receptor, Melanocortin, Type 1↗
PubMed2003

Postharvest resistance in hard spring and winter wheat varieties of the northern Great Plains to the lesser grain borer (Coleoptera: Bostrichidae).

Wheat (Triticum aestivum L.) varietal resistance to the lesser grain borer, Rhyzopertha dominica (F), was evaluated in hard spring and winter wheat produced 1997, 1998 (Bozeman, Montana). We tested the hypothesis that six Montana-grown spring wheat varieties, 'Ernest', 'Scholar', 'Hi-Line', 'McNeal', 'Newana', and 'Amidon', were equally and strongly resistant to R. dominica at low moisture contents (9-10%). Mortality/Feeding damage occurred in all varieties. In most assays, Ernest had significantly greater feeding damage from R. dominica than other varieties, usually not significantly different from the susceptible control. Mean adult mortality was significantly greater in McNeal (93%) and Hi-Line (92%) than in Ernest (34%) and Montana-grown, soft white spring wheat (Penawawa), the susceptible control (36%). In 9 wk, twice as many adult progeny were produced on Ernest than on McNeal, Hi-Line, or Scholar. We also compared three Montana-grown winter wheat varieties for resistance to R. dominica attack at low moisture contents (9-10%). Significantly more mortality after 6 wk was associated with all winter wheat varieties than the susceptible control. In 'Nuwest', 'Rocky', and 'Vanguard', significantly fewer progeny were produced than in the susceptible control; these varieties appeared more resistant. 'Tiber' and 'Neeley', in contrast, appeared more susceptible than other winter wheat varieties evaluated. Susceptibility decreased significantly with a 1.2% decrease in moisture content. Percentage of total protein was positively correlated with percentage of sound kernels and negatively with total progeny (r2 = -0.69). Kernel hardness was positively correlated with percentage of sound kernels, but negatively correlated with total progeny (r2 = -0.87) and dry weight loss.

Animals↗
PubMed1995

Rapid freezing induces winter injury symptomatology in red spruce foliage.

Red spruce (Picea rubens Sarg.) suffers frequent and extensive injury to current-year foliage during the winter. Experimental freezing of red spruce foliage at cooling rates > 10 degrees C min(-1) induced visible symptomatology similar to natural winter injury at the branch, needle and cellular levels. Such damage was associated with a low-temperature exotherm near -10 to -12 degrees C, a loss in needle fluorescence, massive cellular disruption, foliar discoloration, and low needle survival. Susceptibility of individual trees to rapid freezing injury was associated with historical winter injury patterns and alterations in foliar nutrition. We conclude that anthropogenic deposition may alter the sensitivity of trees to winter injury caused by rapid temperature changes.

Journal Article↗
PubMed1999

Role of roots in winter water relations of Engelmann spruce saplings.

Roots play a role in maintaining foliar water balance in subalpine conifer saplings during winter. We used deuterium-labeled water to demonstrate that roots of Engelmann spruce (Picea engelmannii Parry) take up water during the late-winter-early spring period. Based on a root severing experiment, we conclude that small, snow-covered saplings were largely dependent on root water uptake to meet winter transpiration needs, whereas larger saplings relied more on water stored in stem sapwood. Both water uptake and water stored in roots appeared to be critical for the survival of saplings exposed above the snowpack during the late-winter-early spring period, when sap reserves were insufficient to meet increasing transpirational demands.

Journal Article↗
PubMed2002

Winter embolism, mechanisms of xylem hydraulic conductivity recovery and springtime growth patterns in walnut and peach trees.

Xylem vessels of Prunus persica Batsch (peach) and Juglans regia L. (walnut) are vulnerable to frost-induced embolism. In peach, xylem embolism increased progressively over the winter, reaching a maximum of 85% loss of hydraulic conductivity (PLC) in early March. Over winter, PLC in walnut approached 100%, but the degree of xylem embolism varied during the winter, reflecting the ability of walnut to generate positive xylem pressures in winter and spring. In contrast, positive xylem pressures were not observed in peach. Controlled freeze-thaw experiments showed that frost alone is insufficient to increase embolism in peach; evaporative conditions during thawing are also required. However, when both species were protected from frost, PLC was zero. At bud break, there was complete recovery from embolism in walnut, whereas PLC remained high in peach. Three mechanisms responsible for the restoration of branch hydraulic conductivity were identified in walnut: the development of stem pressure, the development of root pressure and the formation of a new ring of functional xylem, whereas only one mechanism was observed in peach (new functional ring). The climatic conditions necessary for the manifestation of these mechanisms were investigated.

Juglans↗
PubMed2004

Temperature effects on xylem sap osmolarity in walnut trees: evidence for a vitalistic model of winter embolism repair.

We studied the effect of temperature on the carbohydrate status of parenchyma cells during winter in relation to the efflux and influx of sugars between parenchyma cells and xylem vessels in 1-year-old twigs of walnut (Juglans regia L.). The mechanism of sugar transfer between contact cells and vessels was also investigated. We obtained new insights into the possible osmotic role of sugars, particularly sucrose, in stem pressure formation and winter embolism repair. Accumulation of sucrose in the xylem sap during winter was mainly influenced by: (1) abundant conversion of starch to sucrose in the symplast at low temperatures; (2) sucrose efflux into the apoplast at low temperatures (1 degrees C); and (3) inefficient sugar uptake at low temperatures, although efficient sugar uptake occurred at 15 degrees C. We hypothesize that a diethyl pyrocarbonate (DEPC)-sensitive protein mediates facilitated diffusion of sucrose from parenchyma cells to xylem vessels (efflux) in walnut. We discuss the possible occurrence of active H+-sucrose symports and the coexistence of both influx and efflux processes in walnut in winter and the modulation of the relative importance of these flows by temperature.

Carbohydrates↗
PubMed1991

Winter desiccation and injury of subalpine red spruce.

Montane red spruce (Picea rubens Sarg.) in the northeastern United States has undergone a decline during the past two decades. One symptom associated with the decline syndrome is the episodic browning of first-year foliage in early spring. To examine the potential role of winter desiccation in this browning, the water relations of red spruce foliage in a subalpine forest on Mt. Moosilauke, New Hampshire, USA, were monitored from January to May, 1989. All sampled trees lost water during the winter and the first-year foliage on some trees turned brown in early spring. The relative water content of first-year shoots during the winter was a significant predictor of spring browning; red spruce trees that showed browning had desiccated faster and reached lower relative water contents. Damaged trees also had more closely packed needles and lower cuticular resistances to water loss. The first-year shoots had a significantly lower average relative water content than older shoots before and after browning. Cuticular resistance to water loss decreased with elevation. Sun-exposed shoots lost more water than shaded shoots because of solar heating of needles. Winter desiccation can occur before the decline-related spring browning of red spruce foliage.

Journal Article↗
PubMed1994

Low bone mineral content and high serum osteocalcin and 1,25-dihydroxyvitamin D in summer- versus winter-born newborn infants: an early fetal effect?

Seasonal differences in bone mineral indices have not been studied in newborn infants. In adults, indicators of bone metabolism may show seasonal variations. In postneonatal infants and possibly in adults, vitamin D metabolism shows seasonal variations. We hypothesized that in winter-born infants, the bone mineral content is low and serum osteocalcin is high, related to increased bone turnover and high serum 1,25-dihydroxyvitamin D [1,25(OH)2D]. We studied 246 healthy, term appropriate-for-gestation infants in winter (January through March; 140 children) and summer (July through September; 106 children). The bone mineral content (BMC) of the one-third distal radius was measured before 3 days of age by photon absorptiometry. Significant seasonal differences were found: summer-born infants had significantly lower BMC, higher serum osteocalcin and 1,25(OH)2D, and lower serum total calcium than winter-born infants. Seasonal differences in BMC remained significant after adjusting for race and sex. BMC was not correlated with serum biochemical measures. Thus, summer-born newborn infants have low BMC and high serum osteocalcin and 1,25(OH)2D than winter-born infants; these findings are the opposite of adult findings. We suggest that seasonal effects on fetal bone operate especially in early pregnancy (approximately 6 months before birth) resulting in a "phase effect" and opposite findings from later life.

Black People↗
PubMed2001

Postponed reproduction as an adaptation to winter conditions in Drosophila melanogaster: evidence for clinal variation under semi-natural conditions.

Patterns of climatic adaptation in drosophila and other insects have largely been inferred from laboratory comparisons of traits that vary clinally. Here, we extend this research to comparisons under semi-natural conditions. To test for clinal variation in reproductive patterns and survival over winter, Drosophila melanogaster populations were initiated from seven collection sites along the eastern coast of Australia, ranging from tropical to temperate regions. The fecundity and survival of these populations were monitored in field cages at a temperate location until all adults had died more than 5 months later. Total fecundity showed a curvilinear relationship with latitude, due to higher egg production by high- and low-latitude populations. Adults from temperate locations survived winter conditions better than those from subtropical populations but not tropical ones. There was a linear cline in the timing of egg production: temperate populations produced eggs later than populations from lower latitudes. This cline is likely to be adaptive because egg-to-adult viability experiments indicated that only eggs laid in spring developed successfully to the adult stage. There was no evidence for climatic adaptation in the immature stages. The adult mortality rate increased gradually over winter, and in some populations was also correlated with the minimum ambient temperature. These results indicate that adaptation to winter conditions in D. melanogaster has involved shifts in reproductive patterns.

Acclimatization↗
PubMed2005

Winter resource wealth drives delayed dispersal and family-group living in western bluebirds.

Delayed dispersal, where offspring remain with parents beyond the usual period of dependence, is the typical route leading to formation of kin-based cooperative societies. The prevailing explanations for why offspring stay home are variation in resource wealth, in which offspring of wealthy parents benefit disproportionately by staying home, and nepotism, where the tendency for parents to be less aggressive and share food with offspring makes home a superior place to wait to breed. These hypotheses are not strict alternatives, as only wealthy parents have sufficient resources to share. In western bluebirds, Sialia mexicana, sons usually delay dispersal until after winter, gaining feeding advantages through maternal nepotism in a familial winter group. Experimentally reducing resource wealth (mistletoe) by half on winter territories caused sons to disperse in summer, even though their parents remained on the territory during the winter. Only 8% of sons remained with their parents on mistletoe-removal territories compared to 50% of sons on control territories (t(9,10)=3.33, p<0.005). This study is the first to demonstrate that experimentally reducing wealth of a natural food resource reduces delayed dispersal, facilitating nepotism and family-group living. The results clarify the roles of year-round residency, resource limitation and relative wealth outside the breeding season in facilitating the formation of kin-based cooperative societies.

Animals↗
PubMed2003

Winter at the alpine timberline. Why does embolism occur in norway spruce but not in stone pine?

Conifers growing at the alpine timberline are exposed to frost drought and freeze-thaw cycles during winter-stress factors known to induce embolism in tree xylem. The two dominant species of the European Central Alps timberline were studied: Norway spruce (Picea abies [L.] Karst) and stone pine (Pinus cembra), which usually reaches higher altitudes. We hypothesized to find embolism only at the timberline and to observe less embolism in stone pine than in Norway spruce due to avoidance mechanisms. Seasonal courses of embolism and water potential were studied at 1,700 and 2,100 m during two winter seasons and correlated to vulnerability (to drought-induced embolism), leaf conductance, and micrometeorological data. Embolism was observed only at the timberline and only in Norway spruce (up to 49.2% loss of conductivity). Conductivity losses corresponded to low water potentials (down to -3.5 MPa) but also to the number of freeze-thaw events indicating both stress factors to contribute to embolism induction. Decreasing embolism rates-probably due to refilling-were observed already in winter. Stone pine did not exhibit an adapted vulnerability (50% loss of conductivity at -3.5 MPa) but avoided critical potentials (minimum -2.3 MPa): Cuticulare conductance was 3.5-fold lower than in Norway spruce, and angles between needles and axes were found to decrease in dehydrating branches. The extent of conductivity losses in Norway spruce and the spectrum of avoidance and recovery mechanisms in both species indicates winter embolism to be relevant for tree line formation.

Acclimatization↗
PubMed1998

Visualization of cavitated vessels in winter and refilled vessels in spring in diffuse-porous trees by cryo-scanning electron microscopy

Xylem cavitation in winter and recovery from cavitation in the spring were visualized in two species of diffuse-porous trees, Betula platyphylla var. japonica Hara and Salix sachalinensis Fr. Schm., by cryo-scanning electron microscopy after freeze-fixation of living twigs. Water in the vessel lumina of the outer three annual rings of twigs of B. platyphylla var. japonica and of S. sachalinensis gradually disappeared during the period from January to March, an indication that cavitation occurs gradually in these species during the winter. In April, when no leaves had yet expanded, the lumina of most of the vessels of both species were filled with water. Many vessel lumina in twigs of both species were filled with water during the period from the subsequent growth season to the beginning of the next winter. These observations indicate that recovery in spring occurs before the onset of transpiration and that water transport through twigs occurs during the subsequent growing season. We found, moreover, that vessels repeat an annual cycle of winter cavitation and spring recovery from cavitation for several years until irreversible cavitation occurs.

Journal Article↗
PubMed1999

Antifreeze proteins in winter rye leaves form oligomeric complexes

Antifreeze proteins (AFPs) similar to three pathogenesis-related proteins, a glucanase-like protein (GLP), a chitinase-like protein (CLP), and a thaumatin-like protein (TLP), accumulate during cold acclimation in winter rye (Secale cereale) leaves, where they are thought to modify the growth of intercellular ice during freezing. The objective of this study was to characterize the rye AFPs in their native forms, and our results show that these proteins form oligomeric complexes in vivo. Nine proteins were separated by native-polyacrylamide gel electrophoresis from apoplastic extracts of cold-acclimated winter rye leaves. Seven of these proteins exhibited multiple polypeptides when denatured and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After isolation of the individual proteins, six were shown by immunoblotting to contain various combinations of GLP, CLP, and TLP in addition to other unidentified proteins. Antisera produced against individual cold-induced winter rye GLP, CLP, and TLP all dramatically inhibited glucanase activity in apoplastic extracts from cold-acclimated winter rye leaves, and each antiserum precipitated all three proteins. These results indicate that each of the polypeptides may be exposed on the surface of the protein complexes. By forming oligomeric complexes, AFPs may form larger surfaces to interact with ice, or they may simply increase the mass of the protein bound to ice. In either case, the complexes of AFPs may inhibit ice growth and recrystallization more effectively than the individual polypeptides.

Journal Article↗