Interactive effects of temperature and photoperiod on the daily activity and energy metabolism of pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

The daily activity and energy metabolism of pouched mice (Saccostomus campestris) from two localities in southern Africa was examined following warm (25 °C) and cold (10 °C) acclimation under long (LD 14:10) and short (LD 10:14) photoperiol. There was no differential effect of photoperiod on the daily activity or metabolism of pouched mice from the two localities examined, which suggests that reported differences in photoresponsivity between these two populations were not the result of differences in daily organisation. Neverthe-less, there was a significant increase in metabolism at 10 °C, irrespective of photoperiod, even though seven cold-acclimated animals displayed bouts of spontaneous torpor and saved 16.4–36.2% of their daily energy expenditure. All but one of these bouts occurred under short photoperiod, which suggests that short photoperiod facilitated the expression of torpor and influenced the daily energy metabolism of these individuals. As expected for a noctureal species, the amount of time spent active increased following acclimation to short photoperiod at 25 °C. However, there was a reduction in mean activity levels under short photoperiod at 10 °C, possibly because the stimulation of activity by short photoperiod was masked by a reduction in activity during bouts of spontaneous torpor. Cold temperature clearly had an overriding effect on the daily activity and metabolism of this species by necessitating an increase in metabolic heat production and eliciting spontaneous torpor which overrode the effect of short photoperiod on activity at an ambient temperature of 10 °C.Abbreviations 3-ANOVA three-way analysis of variance - %ACT percentage of time spent active - ADMR average daily metabolic rate - M _b body mass - MR metabolic rate - MR_dark metabolic rate recorded during the dark phase - MR_light metabolic rate recorded during the light phase - NST non-shivering thermogenesis - RQ respiratory quotient - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - VO₂ oxygen consumption     

The relative importance of photoperiod and temperature as cues for seasonal acclimation of thermoregulation in pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

Summary The effect of short photoperiod and cold on metabolism and thermoregulation was investigated in pouched mice (Saccostomus campestris: Cricetidae) from three localities in southern Africa which experience contrasting climatic conditions. Mice were initially acclimated to long photoperiod (14L: 10D) at 25°C, followed first by a decline in photoperiod (to 10L: 14D) and then by a fall in temperature (to 10°C). Minimum observed metabolic rate (basal metabolic rate) was unaffected by the decline in photoperiod but increased significantly following cold acclimation. Because minimal thermal conductance remained constant throughout the study the increase in minimum observed metabolic rate caused a decline in lower critical temperature to around 26°C. In contrast to minimum observed metabolic rate, regulatory non-shivering thermogenesis improved significantly following the decline in both photoperiod and temperature. However, pouched mice from the warmest locality were significantly less responsive to photoperiod than those from the other two localities whose survival might depend upon their ability to accurately predict seasonal changes in temperature. Neither photoperiod nor temperature had any effect on body mass, yet pouched mice from the most arid locality, where food supply might be unpredictable, were significantly smaller and had lower total energy requirements than those from areas experiencing higher annual rainfall. These results indicate that S. campestris displays considerable geographical variation in energy requirements together with differences in the use of photoperiod as an anticipatory cue for predicting the onset of winter. These differences appear to be related to the availability of energy and the relative severity of climatic conditions in each locality.Abbreviations ANOVA analysis of variance - BMR basal metabolic rate - C _m minimal thermal conductance - M _b body mass - MOMR minimum observed metabolic rate - MWU Mann-Whitney U-test - NA noradrenaline - NST non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a ambient temperature - T _b body temperature - T _1c lower critical temperature - oxygen consumption - maximum - following NA injection     

Summer acclimatization in the short-tailed field vole,Microtus agrestis

We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles,Microtus agrestis, during exposure to naturally increasing photoperiod and ambient temperature. These parameters were first measured in winter-acclimatized voles (n=8) and then in the same voles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and nonshivering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship between basal metabolic rate and noradrenaline-induced metabolic rate. Body mass was significantly higher in summer-acclimatized compared to winter-acclimatized voles. There was a significant positive relationship between body mass and noradrenaline-induced metabolic rate in both winter-acclimalized and summer-acclimatized voles; however, there was no relationship between basal metabolic rate and body mass in either seasonal group of voles. Body temperature after measurements of basal metabolic rate was not significantly different in the seasonal cohorts of voles. However, body temperature was significantly higher in winter-acclimatized compared to summer-acclimatized voles after injection of noradrenaline. Previously we have found that a long photoperiod was not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized voles during cold exposure, since basal metabolic rate increased to compensate for a reduction in regulatory nonshivering thermogenesis. Here we found that a combination of increased ambient temperature and photoperiod did significantly reduce thermogenic capacity in winter-acclimatized voles. This provided evidence that the two aspects of non-shivering thermogenesis, obligatory and regulatory, are stimulated by different exogenous cues. Summer acclimatization in the shorttailed field vole is manifest as a significant decrease in both basal and noradrenaline-induced metabolic rate, combined with a significant increase in body mass.Abbreviations ANCOV A analysis of covariance - BAT brown adipose tissue - BM body mass - BMR basal metabolic rate - NST non-shivering thermogenesis - NA noradrenaline - V the maximum V recorded following mass specific injection of noradrenaline - V the maximum V recorded following mass specific injection of saline - T _a ambient temperature - T _b rectal body temperature - T _1c lower critical temperature - UCP uncoupling protein - V oxygen consumption     

Seasonal adjustments in body mass and thermogenesis in Mongolian gerbils (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>): the roles of short photoperiod and cold

Seasonal adjustments in body mass and thermogenesis are important for the survival of small mammals during acclimatization in the temperate zone. To determine the contributions of short photoperiod and cold temperatures to seasonal changes in thermogenesis and body mass in Mongolian gerbils (Meriones unguiculatus), body mass, basal metabolic rate (BMR), nonshivering thermogenesis (NST), energy intake and energy digestibility were determined in seasonally acclimatized and laboratory acclimated animals. Body mass showed significant seasonal changes and decreased to a minimum in winter. Both BMR and NST increased in winter, and these changes were mimicked by exposing animals to short photoperiod or cold temperatures in the animal house. Digestible energy intake also increased significantly in winter, and also during exposure of housed animals to both short photoperiod and cold. These results suggest that Mongolian gerbils overcome winter thermoregulatory challenges by increasing energy intake and thermogenesis, and decreasing body mass to reduce total energy requirements. Short photoperiod and cold can serve as effective environmental cues during seasonal acclimatization.     

Seasonal adaptation of brown adipose tissue in the Djungarian hamster

Summary The composition and oxidative capacity of brown adipose tissue (BAT) were investigated in Djungarian hamsters kept under natural photoperiod, either indoors at neutralT _a (23°C) or under outdoor conditions. BAT comprises up to 5% of the body weight in summer/indoor hamster, with lipid representing 86% of the total tissue mass. Tissue mass and thermogenic capacity are inversely related during seasonal adaptation: 30% decrease of total DNA, accompanied by extensive lipid depletion, reduces the amount of BAT by almost 60% during acclimatization from summer/indoor to winter/outdoor conditions. Mitochondrial protein in BAT is increased by a factor of 2.6 concomitantly, and by a factor of 4 when related to body weight (body weight reduction 36%).Cytochrome oxidase activity in different brown fat deposits varies by up to 150% in summer/indoor hamsters; depending on the fat pad, the enzyme activity is increased 200%–700% during adaptation to winter/outdoor conditions.Natural photoperiod is decisive in determining the seasonal adaptation of DNA content in BAT and of body weight. Short photoperiod alone may lead to depletion of lipid content of BAT and thus decrease the tissue mass practically to the lowest seasonal level, even though both parameters may be also influenced byT _a. One third of the maximum adaptive increase of tissue mitochondria may be attributed to seasonal changes in photoperiod and up to two thirds toT _a. Photoperiod establishes a fixed fundament of slow-reacting functional adaptation of BAT, whereas the effect of decreasedT _a depends on the rate and duration of cold influence.Abbreviations BAT brown adipose tissue - NST nonshivering thermogenesis - T _a ambient temperature     

Assessing the role of body mass and sex on apparent adult survival in polygynous passerines: a case study of cetti's warblers in central Portugal

Adult survival, an important fitness component, is usually 1) lower in lighter individuals due to their reduced ability to survive winter conditions compared to heavier ones, especially in resident species at northern temperate latitudes and 2) lower in females compared with males due to higher reproductive costs incurred by females. In this paper, a capture–mark–recapture dataset of 649 cetti's warblers Cettia cetti ringed seasonally at two wetlands in central Portugal over an 11‐yr period (2000–2010) was modelled in a multi‐state framework to examine the influence of these individual covariates on apparent adult survival, while controlling for the presence of transient individuals in our study area. The probability of change in mass state (ψ_{Light→Heavy}, ψ_{Heavy→Light}) during the annual cycle was also estimated. Overall, birds survived better during spring–summer (breeding/moulting periods) compared with autumn–winter, but there was no effect of body mass on apparent adult survival probability. The modelling detected a significant interaction between sex and season, in which resident females survived better than resident males in spring–summer (?_RF= 0.857 ± 0.117 and ?_RM= 0.698 ± 0.181) while the opposite pattern was found in autumn–winter (?_RM= 0.440 ± 0.086 and ?_RF= 0.339 ± 0.084). In addition, cetti's warblers had a tendency to lose mass in spring–summer (ψ_{Heavy → Light}= 0.560 ± 0.063) and to regain mass in autumn–winter (ψ_{Light→Heavy}= 0.701 ± 0.069). This pattern of body mass change during the annual cycle may reflect energetic costs to reproduction and moulting, and/or a response to increased starvation risk during winter. High body mass, however, did not increase adult survival in this population presumably due to the relatively mild winter weather prevailing in central Portugal. Survival estimates are more likely to be explained by important ecological and behavioural differences between the two sexes in polygynous passerines. Our results highlight that studies aiming to identify the main factors shaping survival and individual fitness in polygynous species should be conducted during different phases of their annual cycle.     

Seasonal acclimatization of metabolism in Eurasian tree sparrows (Passer montanus)

Acclimatization to winter conditions is an essential prerequisite for survival of small passerines of the northern temperate zone. Changes in photoperiod, ambient temperature and food availability trigger seasonal acclimatization in physiology and behavior of many birds. In the present study, seasonal adjustments in several physiological, hormonal, and biochemical markers were examined in wild-captured Eurasian tree sparrows (Passer montanus) from the Heilongjiang Province in China. In winter sparrows had higher body mass and basal metabolic rate (BMR). Consistently, the dry mass of liver, heart, gizzard, small intestine, large intestine and total digestive tract were higher in winter than in that in summer. The contents of mitochondrial protein in liver, and state-4 respiration and cytochrome c oxidase (COX) activity in liver and muscle increased significantly in winter. Circulating level of serum triiodothyronine (T₃) was significantly higher in winter than in summer. Together, these data suggest that tree sparrows mainly coped with cold by enhancing thermogenic capacities through increased organ masses and heightened activity of respiratory enzymes activities. The results support the view that prominent winter increases in BMR are manifestations of winter acclimatization in tree sparrows and that seasonal variation in metabolism in sparrows is similar to that in other small temperate-wintering birds.     

Is the annual cycle in body weight of pouched mice (Saccostomus campestris) the result of seasonal changes in audit size or population structure?

The annual cycle in body weight of pouched mice ( Saccostomus campestris ) was examined among 104 specimens which were collected throughout the year in the Transvaal province of South Africa. Each specimen was assigned to one of five age classes using toothwear characteristics although none of them belonged to the youngest age class. There was no significant effect of sex on body weight but older individuals were significantly heavier than younger ones. Pooled data from both sexes displayed seasonal variation in body weight with significantly heavier animals in the wet season (December-March) than during the dry season (June-September). However, there was no significant difference between the age structure of the population at these times. Instead, pouched mice in the two younger age classes were significantly lighter in the dry season compared to the wet season, while older individuals maintained a relatively constant body weight throughout the year. These results suggest that the annual cycle in body weight of S. campestris is caused by a reduction in body weight of young animals which lose weight in winter as an adaptation to limit their energy requirements when food availability declines.     

Seasonal variations in basal metabolic rate, lower critical temperature and responses to temporary starvation in the arctic fox (Alopex lagopus) from Svalbard

Metabolic rates of four resting, post-absorptive male adult summer- and winter-adapted captive arctic foxes (Alopex lagopus) were recorded. Basal metabolic rates (BMR) varied seasonally with a 36% increase from winter to summer, while body mass was reduced by 17% in the same period. The lower critical temperature (T _1c) of the winter-adapted arctic fox was estimated to −7°C, whereas T _lc during summer was 5°C. The similarity of these values, which are much higher than hitherto assumed (e.g. Scholander et al. 1950b), is mainly due to a significantly (P<0.05) lower BMR in winter than in summer. Body core (stomach) temperature was stable, even at ambient temperatures as low as −45°C, but showed a significant (P<0.05) seasonal variation, being lower in winter (39.3±0.33°C) than in summer (39.8±0.16°C). The thermal conductivity of arctic fox fur was the same during both seasons, whereas the thermal conductance in winter was lower than in summer. This was reflected in an increase in fur thickness of 140% from summer to winter, and in a reduced metabolic response to ambient temperatures below T _lc in winter. Another four arctic foxes were exposed to three periods of forced starvation, each lasting 8 days during winter, when body mass is in decline. No significant reduction in mass specific BMR was observed during the exposure to starvation, and respiratory quotient was unchanged at 0.73±0.02 during the first 5 days, but dropped significantly (P<0.05) to 0.69±0.03 at day 7. Locomotor activity and body core (intraperitoneal) temperature was unaltered throughout the starvation period, but body mass was reduced by 18.5±2.1% during these periods. Upon re-feeding, locomotor activity was significantly (P<0.05) reduced for about 6 days. Energy intake was almost doubled, but stabilised at normal levels after 11 days. Body mass increased, but not to the level before the starvation episodes. Instead, body mass increased until it reached the reduced body mass of ad libitum fed control animals. This indicates that body mass in the arctic fox is regulated according to a seasonally changing set point.     

A preliminary study on the seasonal body temperature rhythms of the captive mountain hare (Lepus timidus)

The mountain hare (Lepus timidus) is a year-round active herbivore adapted to survive the boreal winter. Captive mountain hares (N = 4) were implanted with intraabdominal thermosensitive loggers to record their core body temperature (T_b) for a year and during food deprivation (8–48 h) in summer and winter. The average T_b was 38.7 ± 0.01 °C in summer and 38.3 ± 0.01 °C in winter. The yearly T_b correlated positively with the ambient temperature. The 24-h T_b was the highest from late scotophase to early photophase in summer and winter and the lowest during middle-late photophase in summer or during early-middle scotophase in winter. The range of the 24-h oscillations in T_b increased in three animals in winter. Food deprivation did not induce hypothermia in summer or winter. These preliminary data suggest that the mountain hare can spare a modest amount of energy with the wintertime reduction in T_b.     

Seasonal changes in body mass and thermogenesis in tree shrews (Tupaia belangeri): The roles of photoperiod and cold

Environmental factors play an important role in the seasonal adaptation of body mass and thermogenesis in small, wild mammals. To determine the contributions of photoperiod and cold on seasonal changes in energy metabolism and body mass, the resting metabolic rates (RMR), nonshivering thermogenesis (NST), energy intake and gut morphology of the tree shrews were determined in winter and summer and in laboratory acclimated animals. Body mass, RMR and NST increased in winter, and these changes were mimicked by exposing animals to short-day photoperiod or cold in the animal house. Energy intake and digested energy also increased significantly in winter, and also during exposure of housed animals to both short-day photoperiod and cold. The lengths and weights of small intestine increased in winter. These results indicated that Tupaia belangeri overcomes winter thermoregulatory challenges by increasing energy intake and thermogenesis, and adjusted gut morphology to balance the total energy requirements. Short-day photoperiod and cold can serve as environmental cues during seasonal acclimatization.     

Torpor patterns in the pouched mouse (Saccostomus campestris ; Rodentia): a model animal for unpredictable environments

Patterns of spontaneous and induced daily torpor were measured in the Afrotropical pouched mouse (77–115?g), Saccostomus campestris, in response to photoperiod, temperature, and food deprivation, using temperature telemetry. Photoperiod had no influence on the incidence, depth, or duration of daily torpor in either males and females. Although the testis size index decreased in response to food deprivation and photoperiod by a maximum of 24%, full testis regression did not occur. Torpor bout duration was, on average, 5.3?h, independent of photoperiod and ambient temperature. Males did not enter torpor in response to food deprivation but did in response to low ambient temperature, though significantly less frequently than females. At normothermia, the body temperatures (daily minimum, mean, maximum) of males were significantly lower than those of females. Minimum body temperatures of both males and females during torpor did not fall below 20?°C at an ambient temperature of 15?°C. The patterns of torpor measured here differ from those observed in species from strongly seasonal environments. They suggest adaptation to an environment rendered unpredictable by the El Niño Southern Oscillations. As an aseasonal, opportunistic breeder capable of year-round adaptive hypothermia, the pouched mouse represents an excellent model animal for research on physiological and behavioral adaptations to unpredictable environments.     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.     

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

Summary 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 andApodemus 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. InClethrionomys 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, whereasA. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in theApodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas inClethrionomys 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 inClethrionomys andApodemus.Abbreviations BAT brown adipose tissue - BMR basal metabolic rate (resting metabolic rate at thermoneutrality) - BW body weight - COX cytochrome c oxidase - GDP guanosine diphosphate - MP mitochondrial protein - NA noradrenaline - NST nonshivering thermogenesis - NSTcap NST capacity (NST maximum minus BMR) - T _a ambient temperature     

How photoperiod influences body temperature selection in Lacerta viridis

Summary European green lizards, Lacerta viridis, show a distinct annual cycle in their day and nighttime selected body temperature (T _b) levels when monitored under natural photoperiod. The amplitude between daily photophase and scotophase temperatures varies throughout the year. Highest body temperatures with smallest day/night variation are selected from May through July. Throughout fall, the difference between day and nighttime selected T _b levels increases. Lizards inevitably enter a state of winter dormancy which terminates daily rhythmicity patterns. Under natural photoperiodic conditions, cessation of dormancy occurs spontaneously by mid-March, regardless whether high temperatures are available or not. Lacerta viridis respond to an artificial long photoperiod (16 h light, 8 h dark) at all times of the year with modifications in both diel patterns and levels of selected T _b to summer-like conditions. When, however, the natural photoperiod at different phases in the annual cycle is held constant for six to eight weeks, T _b selection of Lacerta viridis also remains stable at the level corresponding to the prevailing photoperiod. These results implicate that the photoperiod is a more prominent Zeitgeber for seasonal cueing of temperature selection than has been surmised in the past. Further, we suggest that the large variations recorded in daily T _b cycles do not imply that this lizard is an imprecise thermoregulator, but rather indicates an important integral process necessary for seasonal acclimatization.     

The effect of season, sex and feeding style on home range area versus body mass scaling in temperate ruminants

Sex-specific estimates of the summer and winter home range area of 19 species of temperate ruminants were collated from the literature. It was predicted that there should be a shallower slope for the home range area against body mass relationship during winter than during summer, as large ruminants can meet more of their energy requirements from the fat reserves deposited during summer than small ruminants. Consequently, relatively large species do not need to range as widely during winter. There was a significant positive relationship between body mass and summer and winter home range area in both females and males. This relationship remained significant when analysed within feeding styles (browser, mixed feeder, grazer), except in mixed feeders in winter. As predicted, slope estimates were significantly lower during winter (b=0.59) than during summer (b=1.28), both before and after controlling for phylogeny. After controlling for phylogeny, browsers had a steeper slope (summer: b=1.48; winter: b=1.07) of the home range area against body mass relationship than did mixed feeders (summer: b=0.75; winter: b=-0.11) or grazers (summer: b=1.10; winter: b=0.34). There was no effect of sex after body mass was controlled for. The effect of season, sex and feeding style on the home range area versus body mass relationship in temperate ruminants is discussed.     

Environmental Determinants of Birth Seasonality in Night Monkeys (Aotus azarai) of the Argentinean Chaco

The night monkeys (Aotus azarai) of Formosa, Argentina provide an opportunity to investigate the influences of ambient temperature and photoperiod on reproduction in a highly seasonal environment: the Chaco. Between 1997 and 2000, we collected data to evaluate the relationship between rainfall, ambient temperature, photoperiod and food availability and the annual distribution of mating behavior and births in 15 groups of monkeys in the forests of the Eastern Argentinean Chaco. Our data show that the area is highly seasonal, characterized by significant fluctuations in rainfall, temperature, photoperiod and food availability. There are two rain peaks in April and November and a dry season lasting from June to August. Monthly mean temperatures were on average 11°C lower during winter months than they were during summer months. Temperatures <10°C and >33°C were also frequent through the year. Days are 3 h longer during the summer than during the winter months. Insect abundance and the percentage of tree species producing fruits, flowers or new leaves reached a low in the coldest winter months. Mating was infrequent, and we only observed it between May and September. Half the births (n = 13) occurred during a 2-week period in October. Infant survival during the first 6 mo of life was high (96%). Our findings suggest an environmental control of reproduction. Changes in photoperiod and temperature may promote reproductive activity in females that might conceive and begin pregnancy at a time void of high temperatures that could be metabolically challenging.     

Local variation in overwintering stages ofPanonychus akitanus Ehara (Acarina: Tetranychidae)

The overwintering behaviour ofPanonychus akitanus Ehara was compared in a population (Sapporo) overwintering as the egg and the adult female and in a population (Tomakomai) overwintering in the egg stage only. In both populations, winter eggs were larger in size and darker in colour than summer eggs, and females laying winter eggs showed clear differences in body colour and behaviour from summer females. Both populations produced winter eggs in response to short photoperiods, and the critical photoperiod was between 13.0 and 13.5 h in the Sapporo population and between 13.5 and 14.0 h in the Tomakomai population. The hatchability of winter eggs of the Sapporo population collected from the field began to increase in November, and that of the Tomakomai population in December. In the Sapporo population, a 40-day or more exposure to 5°C promoted hatching of winter eggs, and a 50-day exposure of females which had previously laid some winter eggs to 5°C induced the production of summer eggs. Females of the Sapporo population laid winter eggs in autumn, and then themselves overwintered as well, and produced summer eggs in the following spring. These females were called winter-habit females.The winter eggs of both populations were diapausing. However, the winter-habit females of the Sapporo population were not reproductively inactive and their condition of diapause was not certain. The ecological significance of the winter-habit females in the Sapporo population is discussed.     

黑线仓鼠体重和能量代谢的季节性变化

为阐明小型哺乳动物体重和能量代谢的季节性变化以及生理调节机制,将黑线仓鼠驯化于自然环境下12个月,测定其体重、能量收支、身体组织器官和血清瘦素水平的季节性变化。黑线仓鼠能量摄入和支出的季节性变化显著,冬季摄入能、基础代谢率(BMR)、非颤抖性产热(NST)显著高于夏季。体重季节性变化不显著,但身体组织器官重量呈现显著的季节性变化,冬季肝脏、心脏、肾脏以及消化道重量显著高于夏季。体脂含量夏季最高,冬季最低,冬季显著低于夏、秋和春季(P <0.01)。血清瘦素水平的季节性变化显著,夏季瘦素水平比秋、冬季分别高88.2% 和52.4% (P <0.05)。结果表明,黑线仓鼠体重维持季节性稳定,与“调定点假说”的预测不同;但脂肪含量和血清瘦素季节性变化显著,符合该假说。夏季血清瘦素升高具有抑制能量摄入的作用,冬季血清瘦素可能是促进代谢产热的重要因子,瘦素对能量代谢和体重的调节作用与气候的季节性变化有关。       

Photoperiodic and ambient temperature control of the annual body mass cycle in Svalbard ptarmigan

The present study describes the photoperiodic control of annual body mass changes in captive. Svalbard ptarmigan, in particular the onset of autumnal increase and midwinter decrease in fat content under natural and simulated daylight-conditions in Tromsø (69° 46 N). Autumnal fattening commences when the birds become photorefractory and presumably depends on this condition. At present it is not known if any causal relationship is involved. Under outdoor ambient temperature, body mass begins to decline in November. However, when Svalbard ptarmigan are caged indoors at higher ambient temperatures and exposed to natural or simulated annual changes in daylength, body mass remains high until February. In these birds the depletion of fat stores appears to be triggered by the increasing daylength, since body mass remained high under permanent exposure to short days throughout spring but decreased promptly following photostimulation in May. When ptarmigan caged indoors were starved in midwinter body mass fell but increased briefly upon refeeding and thereafter declined as in the control birds throughout spring. This indicates that the winter body mass profile in Svalbard ptarmigan is not merely the passive outcome of shifts in the energy expenditure associated with thermoregulation, and that a sliding set point for body mass exists and is temporally fixed at the seasonal maximum in mid winter in birds caged under indoor ambient temperatures. The possibility is discussed that the decline in body mass seen outdoors may be associated with the increased hypothalamus-pituitary-gonadal activity which follows the breaking of photorefractoriness, and that this activity is sufficiently suppressed in Svalbard ptarmigan caged indoors under exposure to short days, to delay the reduction until they are photostimulated.Abbreviations BM body mass - GH growth hormone - HPG hypothalamic-pituitary-gonadal system - LL continous light - NL natural light - SD short day (4 hours light per day) - SL simulated annual changes in daylength - T _a ambient temperature