Seasonal and interannual variation in the energetic condition of adult male Atlantic sharpnose shark Rhizoprionodon terraenovae in the northern Gulf of Mexico

One hundred and thirty Atlantic sharpnose shark Rhizoprionodon terraenovae livers were collected from April 1999 to October 2001 from inshore waters of the Mississippi Sound to investigate seasonal and inter‐annual variation in their energetic condition. A decline in the hepato‐somatic index ( I _H) was observed from 1999 to 2001. In addition, I _H, liver specific energy content and total energy content were lowest during the summer and highest during the spring and autumn, while liver water content was highest during the summer and lowest during the spring and autumn.     

Age and growth analysis of the mosshead sculpin Clinocottus globiceps Girard 1857 (Pisces: Cottidae) from Helby Island, British Columbia

The age and growth of the cottid fish Clinocottus globiceps Girard from tidepools at Helby Island, British Columbia, Canada were investigated with the aid of whole saccular otoliths (sagittae); ages were validated by marginal increment analysis. Four hundred and twenty five specimens were examined from 214 females and 211 males. Marginal increment analysis on specimens with one to three opaque zones suggested an annual ring deposition in sagittae during the late autumn and spring months.
The C. globiceps population was composed of individuals from less than 1 year to 5 years of age for fish measuring between 5–120 mm standard length. Growth was faster for younger than for older age groups. Lengths-at-age data were fitted to the Gompertz growth model, and estimates of the model parameters L₀, G and g were 26.7 mm 1.58 and 0.30 for pooled cohorts, respectively. The highest levels of growth occurred during late spring and early summer, when water temperatures were at maximum and food was most abundant. The lowest levels of growth occurred during the autumn and winter months.     

Seasonal dynamics of invertebrate drift in a Hong Kong stream

Drift samples were taken with paired nets on 19 occasions over a 12-month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m^-3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.
Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T₁ (Diptera). Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T₁, Polymorphanisus astictus (Trichoptera), Helodes #1 and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring ( Indobaetis sp., Cinygmina T₁, Serratella T₂), autumn ( Baetiella sp., Pseudocloeon T₂), or spring and autumn ( Baetis nr pseudofrequentus ) peaks which were not clearly related to water temperature. In only two cases ( A. maculatus and P. astictus ) was TPKFS drift seasonality associated with life-cycle events. Overall, there was no evidence of community-level trends in the periodicity of stream drift in this seasonal tropical habitat.     

Seasonal, diel and ontogenetic variation in feeding patterns of small yellow croaker in the central Yellow Sea

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis , sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and >30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, L _S) studied. The importance of fishes and decapods increased with L _S, whereas euphausiids, copepods and amphipods decreased in importance with L _S. Dietary breadth increased markedly for adults. A positive relationship was found between L _S and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker.     

Seasonal differences in photosynthesis between the C3 and C4 subspecies of Alloteropsis semialata are offset by frost and drought

The regional abundance of C₄ grasses is strongly controlled by temperature, however, the role of precipitation is less clear. Progress in elucidating the direct effects of photosynthetic pathway on these climate relationships is hindered by the significant genetic divergence between major C₃ and C₄ grass lineages. We addressed this problem by examining seasonal climate responses of photosynthesis in Alloteropsis semialata , a unique grass species with both C₃ and C₄ subspecies. Experimental manipulation of rainfall in a common garden in South Africa tested the hypotheses that: (1) photosynthesis is greater in the C₄ than C₃ subspecies under high summer temperatures, but this pattern is reversed at low winter temperatures; and (2) the photosynthetic advantage of C₄ plants is enhanced during drought events. Measurements of leaf gas exchange over 2 years showed a significant photosynthetic advantage for the C₄ subspecies under irrigated conditions from spring through autumn. However, the C₄ leaves were killed by winter frost, while photosynthesis continued in the C₃ plants. Unexpectedly, the C₄ subspecies also lost its photosynthetic advantage during natural drought events, despite greater water-use efficiency under irrigated conditions. This study highlights previously unrecognized roles for climatic extremes in determining the ecological success of C₃ and C₄ grasses.     

Seasonal variation in freezing tolerance of the New Zealand alpine cockroach Celatoblatta quinquemaculata

1. The cold hardiness of the alpine cockroach Celatoblatta quinquemaculata was investigated. This species is found at 1360 m a.s.l. beneath schist slabs on the Rock and Pillar Range (Central Otago, New Zealand). Cockroaches were collected monthly from January to December 1996, and their LT₅₀ and supercooling points determined.
2. Celatoblatta quinquemaculata was freezing tolerant throughout the year, with a lower lethal temperature in winter of – 8.9 °C. Celatoblatta quinquemaculata was also found frozen under rocks in the field when the under-rock temperature was below – 3 °C, and could survive being frozen at – 5 °C for 4 days in the laboratory.
3. There was a marked decrease in LT₅₀ temperature from – 5.5 °C in April to – 7.5 °C in May. This coincides with decreasing temperatures from summer through autumn to winter, during which temperatures beneath snow-covered rocks may reach – 7.3 °C.
4. Supercooling points fluctuated during the year, with an increase from – 4.2 °C in autumn to – 3.4 °C in winter. Supercooling point was highest in spring, and changes in supercooling point do not appear to be related to changes in LT₅₀.
5. Recordings of environmental temperatures from the Rock and Pillar Range suggest that cockroaches may undergo up to twenty-three freeze–thaw cycles in the coldest month of the year, and that they may remain frozen for periods of up to 21 h. Maximum cooling rates recorded in the field (0.01 °C min^–1) were 100-fold slower than laboratory cooling rates, so survival estimates from laboratory experiments may be underestimates.     

To fast or feed: an alternative life history for anadromous brook trout Salvelinus fontinalis overwintering within a harbour

The seasonal feeding pattern of sea‐run brook trout Salvelinus fontinalis was studied from November to May 2010–2012 in Antigonish Harbour, Nova Scotia, Canada (45° 38′ N; 61° 55′ W). Sixty‐three S. fontinalis (mean ± s.d . fork length = 330 ± 70 mm and mass = 536 ± 351 g) captured had fed predominantly on fishes (Fundulidae and Gasterosteidae). Percentage of empty stomachs was highest during autumn (18%) and winter (22%) and lowest in spring (7%). Stomach fullness increased from autumn to a maximum during winter, relating to near‐zero body temperatures which may have effectively stopped gastric evacuation. Although feeding occurred during winter (December to March), consumption rates were calculated as negative values, and subsequently returned to positive values in spring (April to May). The over‐winter life‐history strategy of this sea‐run S. fontinalis population appears to be a feeding marine migration in which fish continually increase body condition, representing an alternative to the more common overwintering strategy of starvation in fresh water until spring.     

The effects of temperature and season on the O2 consumption of third-instar larvae of the goldenrod gall fly (Eurosta solidaginis)

Abstract. Third-instar larvae of the goldenrod gall fly ( Eurosta solidaginis Fitch) live inside ball galls on goldenrod plants from summer to the following spring.Because galls are highly exposed to the weather, larvae experience substantial variations in body temperature.This study documents the oxygen consumption of gall fly larvae with regard to the effects of ambient temperature, seasonal conditioning, and prior exposure to subzero temperature.The body mass of larvae doubles between the late summer and the autumn; it subsequently undergoes a modest decline by early winter.The O₂, consumption of field-acclimatized larvae increases with ambient temperature, especially between 0 and 10°C (Q₁₀= 2.6-3.4).The thermal sensitivity of metabolism declines at higher ambient temperatures, most notably during the autumn/early winter.After exposure to 15°C for 1 week, autumn and early winter larvae maintain much lower rates of O₂ consumption than do late summer specimens.Prior exposure to -5°C for 24 h did not influence the O₂ consumption of larvae.Low thermal sensitivity of O₂ consumption, especially at higher ambient temperatures, is an energy-sparing mechanism during seasonal inactivity.Indeed, the persistence of this metabolic pattern in larvae exposed to 15°C suggests that they have entered a state of diapause.     

Effect of season on peripheral resistance to localised cold stress

This study was carried out to determine the effect that seasonal changes have on the effect of localised cold stress on peripheral temperatures using the foot immersion method with a cold water bath. The subjects were six males and four females. The data were obtained in April, July, October and January. Skin temperature of the right index finger, the forehead, the arm, the cheek, the second toe and the instep were measured before, during and after the immersion of the feet in water at 15°C for 10 mins, as well as oxygen consumption before immersion of the feet.The average finger temperature was highest during foot immersion in the summer, next highest in the winter, then spring, and the lowest during foot immersion in the autumn. The finger temperatures during the pre-immersion period in the autumn tended to be lower than in other seasons. The finger temperatures during the pre-immersion period affected the temperature change of the finger during the immersion period. The rate of increase of the toe temperature and the foot temperature during post-immersion in the summer and the spring were greater than those in the autumn and winter. Oxygen consumption during the pre-immersion period in the autumn was significantly lower than in the other seasons (p<0.001 or 0.010). Cooling the feet caused no significant changes in the temperatures the cheek, forehead or forearm. The cheek temperature in the summer and autumn was cooler than corresponding temperatures taken in the winter and spring.     

Seasonal variation in foliar carbon exchange in Pinus radiata and Populus deltoides: respiration acclimates fully to changes in temperature but photosynthesis does not

We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C ( R ₁₀) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature ( Q ₁₀) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity ( R _d/ A _sat) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer.     

Seasonal changes in bacterial and phytoplankton biomass in a subantarctic coastal area (Kerguelen Islands)

The seasonal variations of bacterial and phytoplanktonic biomass were studied during several pluri-annual surveys in the subantarctic Morbihan Bay (Kerguelen Islands, 49 ° 20 S; 70 ° 10 E). Large interannual variation was observed. Phytoplanktonic biomass showed moderate values during winter and autumn. They increased sharply in spring, reaching a maximum value of about 1 mg C l^–1 corresponding to an important depletion of nutrients. A second phytoplanktonic bloom of similar amplitude occurred in late summer. During algal blooms which were roughly associated with optimal values of solar irradiation for the first one and with the highest temperatures for the second one, phytoplanktonic material represented near 100% of particulate and living carbon. Bacteria showed maximal abundance (0.2 to 0.7 mg C l^–1) during summer or autumn. Their relative abundance, which represented less than 1% of the living biomass in spring and summer, can reach more than 95% in autumn and winter.     

Reproductive biology of the threatened golden galaxias Galaxias auratus Johnston and the influence of lake hydrology

Golden galaxias Galaxias auratus (31–235 mm fork length, L _F) were collected monthly from littoral habitats in Lakes Crescent and Sorell, Tasmania, Australia, between July 2000 and December 2002. Spawning habitats were identified and monitored in both lakes, and surveyed in Lake Crescent. Trends in gonado-somatic indices and reproductive stages of development indicated that gonad development in both sexes begins in midsummer and peaks in late autumn to early winter. Males mature at smaller sizes (50% at 52 mm L _F) than females (50% at 76 mm L _F), larger individuals are predominately females (95% of fish ≥138 mm L _F), and overall male to female ratios are female biased ( c . 1:2). Spawning occurs late autumn to early spring (water temperatures = 1·4–9·7° C) with peaks in spawning activity in winter (mean water temperatures <5° C). Demersal adhesive eggs ( c. 1·5 mm diameter) were found on cobble substrata ( c. 20–250 mm diameter) in littoral areas ( c. 0·2–0·6 m deep) and fecundity of fish 71–181 mm L _F ranged from 619 to 14 478 eggs. The rate of change in water level over the 20 days prior to monthly sampling was important in explaining the occurrence of spent fish and this accounted for temporal differences in spawning between the populations. Lake hydrology influences the reproductive cycle of G. auratus by possibly providing a stimulus for spawning and it controls the availability of spawning habitat in Lake Crescent. Seasonal hydrological cycles ( i.e. rises during late autumn to winter) and a minimum water level of 802·20 m Australian Height Datum in Lake Crescent during autumn (above which littoral areas of cobble substratum are inundated) are critical to G. auratus populations.     

Winter lipid depletion of juvenile walleye pollock Theragra chalcogramma in the Doto area, northern Japan

Seasonal variation in body size and nutritional condition of juvenile walleye pollock Theragra chalcogramma was examined to elucidate the mechanism underlying their first-winter survival on the continental shelf of the Doto area, northern Japan, based on monthly samples collected over 2 years. Stored lipid mass was highest during autumn, but 93% (2004) and 80% (2005) of lipids were exhausted by the onset of winter. Lipid levels in the winter of 2004 remained low (7–14% of the autumnal maximum), and there was reduced growth rate until the spring, whereas in 2005 lipid levels were higher and more variable (10–46% of the maximum) and some growth occurred. An analysis of the allometric relationships between body size and stored energy showed that larger individuals accumulated disproportionately more energy in the autumn, but the advantage disappeared prior to the winter. In January 2004, stored lipid energy was low throughout the Doto continental shelf relative to the continental slope area. These results suggest that winter feeding opportunities on the shelf are severely limited but not completely absent. Previous studies have shown that winter temperatures on the shelf are lower than those in the slope area. It is possible that juvenile T. chalcogramma survive winter on the shelf without a high level of pre-winter lipid storage because the occasional feeding in the cold shelf water benefits energy conservation.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.     

Seasonal changes in some photosynthetic properties of Ceratonia siliqua (carob tree) leaves under natural conditions

Rates of photosynthesis and leaf conductance of the leaves of carob trees ( Ceratonia siliqua L.) growing in natural conditions were measured during the course of the seasons to define the effects of the main climatic factors limiting growth in the region: temperature during the winter and water in the summer. The highest photosynthetic rates were measured in spring and autumn and could reach 25 μmol m₋₂ s₋₁ with optimal temperature and available water. Due to lower temperatures (4 to 6°C in the night) these values were frequently around 15 μmol m₋₂ s₋₁ during winter, but the strongest depression was due to prolonged drought in summer. However a reduction in photosynthesis rate down to 5 μmol m₋₂ s₋₁ occurred only after depletion of all the available water in the soil layer up to a depth of 50 cm. In the end of the summer, leaf conductance and water potential were in the order of 20 mmol m₋₂ s₋₁ and −3 MPa respectively. Compared to other trees that make up the Mediterranean sclerophyll forest, the photosynthetic activity of carob is high, and the tree tolerates a considerable depletion of soil water.     

Measuring and modelling environmental influences on photosynthetic gas exchange in Sphagnum and Pleurozium

A mechanistic model has been used to examine the environmental regulation of photosynthetic gas exchange in moss. The effects of water content on conductance to CO₂ and on photosynthetic capacity during desiccation were calculated from the carbon isotope discrimination data of Williams & Flanagan (1996 , Oecologia 108, pp. 38–46) and combined with the biochemical model of Farquhar et al. (1980 , Planta 149, pp. 78–90). The model includes a simple light attenuation function that imparts curvature to the light response curve for net assimilation, enabling the use of physiologically realistic values for the biochemical parameters. Measurements of gas exchange for Sphagnum and Pleurozium were made in an old black spruce ecosystem over a growing season in order to assign values to parameters in the model. The calculated maximum rates of carboxylation by Rubisco ( V _max) were 5, 14 and 6 μ mol m^–2 s^–1 for Sphagnum during the spring, summer and autumn seasons of 1996, respectively. The increase in V _max during the summer was consistent with an increased allocation of resources to the photosynthetic apparatus. In contrast, no seasonal variation in V _max was observed in Pleurozium with average values of 7, 5 and 7 μ mol m^–2 s^–1 during the spring, summer and autumn, respectively.     

Induced seasonal reproductive performance in two breeds of sheep

The objective of the present experiment was to determine whether failure to become pregnant through out-of-season reproductive management regimes is attributable to a failure to stimulate normal corpora lutea (CL) production. Romney ewes and East Friesian Composite (EF) ewes were mated in summer, autumn, winter, and early and late spring after administration of intravaginal progesterone inserts (plus eCG in spring and summer) in a factorial (two breedsxfive mating periods) experimental design. Oestrus rate was determined from mating data, and the numbers of CL were determined by laparoscopy 9 days after ram introduction. Conception rate, pregnancy rate and litter size were determined by transabdominal ultrasonography 62 days after ram introduction. Proportions of ewes displaying oestrus did not differ significantly (75-100%) between seasons or breeds, except for the Romney ewes in summer (67%; P<0.05). Numbers of CL on Day 9 for EF ewes was lowest in autumn (1.5) and winter (1.5), and highest in late spring (2.1; P<0.05). In contrast, Romney ewes had the lowest CL count in summer (1.3), and the highest in autumn (1.8) and winter (1.6; P<0.05). Only in summer was there a difference between breeds (EF 1.8; Romney 1.3; P<0.01). The proportion of ewes that failed to conceive despite having one or more CL present was highest in late spring (EF 41%, Romney 43%), and lowest in autumn (EF 9%, Romney 4%) and winter (EF 14%, Romney 4%; P<0.05). Conception and pregnancy rates followed similar patterns with values for autumn (EF 91%, 91%; Romney 96%, 96%) and June (EF 86%, 82%; Romney 91%, 83%) being significantly (P<0.05) higher than in early (EF 50%, 40%; Romney 54%, 50%) and late spring (EF 44%, 36%; Romney 42%, 36%). Pregnancy rate in summer was higher for EF ewes (60%) than for Romney ewes (39%) but conception rates were not statistically different (EF 68%; Romney 60%). Numbers of foetuses identified at scanning was highest in autumn (1.5) and lowest in late spring (0.5 P<0.001): Litter size in pregnant EF ewes was highest in early spring and lowest in winter (1.8 versus 1.2; P<0.01), but for pregnant Romney ewes was highest in winter and lowest in early spring (1.9 versus 1.3; P<0.001). It was concluded that seasonal differences in the ability of ewes to conceive are not the consequence of failure to display oestrus or to ovulate, but probably are a result of failure of fertilisation or the establishment of pregnancy.     

舟山海域大中型浮游动物群落时空变化及受控要素

为更好地保护舟山海域的渔业资源和生态环境,了解舟山海域浮游动物组成的时空变化,于2014年到2017年对舟山海域33个站位开展4个季节的生态综合调查,结果表明:4个航次共鉴定出浮游动物成体88种和浮游幼体19类,优势种共12种,浮游动物的优势种更替和群落特征季节变化明显,春夏、夏秋、秋冬、冬春相邻季节优势种更替率分别为75%、80%、100%和60%;平均生物量为夏季(176.34 mg/m³)>春季(120.20 mg/m³)和秋季(86.28 mg/m³)>冬季(7.21 mg/m³);平均丰度为夏季(143.97个/m³)>春季(86.30个/m³)>秋季(21.38个/m³)和冬季(26.86个/m³);平均多样性指数:夏季(3.03)>秋季(2.82)>春季(2.05)>冬季(1.71)。舟山海域浮游动物群落具有明显的季节和区域差异,温度、盐度、Chl a和营养盐是影响舟山浮游动物群落时空变化的主要环境因素,其中春季浮游动物群落空间分布主要受盐度的影响,夏季主要受温度、盐度和Chl a的影响,秋季主要受Chl a的影响,冬季主要受悬浮物和溶解氧的影响,而营养盐对每个季节的浮游动物群落分布都有一定的影响。     

Seasonal hyperphagia does not reduce digestive efficiency in an Arctic grazer

Muskoxen (Ovibos moschatus) consume fibrous plants that grow rapidly over the short Arctic summer. We studied responses of eight castrated male muskoxen to a diet of grass hay and mineral supplements during spring, autumn, and winter. Animals gained body mass in spring (239+/-39 kg) as body fat content increased from 26% to 38% of ingesta-free mass in winter without changes in lean mass and protein. Intakes of dry matter (DM) increased by 74% between spring and autumn as digestible energy increased from 554 to 923 kJ kg(-0.75) d(-1) during mass gain. Digestibility of cellulose (72%-76%) was not affected by increasing food intake between spring and autumn but was reduced to 65% in winter. Digestibility of nitrogen compounds was 61%-66%, even though intake increased by 134% between spring and autumn. Excess dietary nitrogen from hay and supplements increased urea concentrations in plasma and urine. High loads of solutes such as potassium did not affect plasma or urinary osmolality but were associated with increased rates of glomerular filtration and urinary excretion. Low intakes of sodium from grasses may limit intake and digestion during summer, but high food intakes can support deposition of nitrogen, calcium, magnesium, copper, and zinc in body tissue even when dietary concentrations are low. Seasonal increases in digestive and metabolic functions allow muskoxen to rapidly accumulate energy and nutrients in body tissue during the short season of plant growth.     

Seasonal Variation in the Orcadian Rhythm of Pulmonary Function in Stable Astthmatic Children who have Nearly Outgrown their Asthma

To study whether nocturnal bronchial obstruction changes during the year, we assessed the circadian FEV₁ variation during four consecutive seasons in 20 children (12 boys; aged 9–12 years) with episodic asthma who were outgrowing their asthma. FEV₁ was determined every 4 h between 10:00 and 10:00 during two consecutive days. The last six FEV₁ values were submitted to cosinor and coefficient of variation (CV) analyses. The seasonal means (SD) in the group 24 h percent predicted FEV₁ was 85.5 (11.4), 81.2 (10.6), 86.0 (11.6), and 82.2 (14.0)% during spring, summer, autumn, and winter, respectively. The difference between the summer and autumn FEV₁ values was statistically significant (p < 0.05). The mean (SD) of the circadian amplitude values was 4.1 (4.3), 6.0 (3.8), 4.9 (3.4), and 7.2 (4.1)% during spring, summer, autumn, and winter, respectively. The difference in amplitude between the spring and winter and between the autumn and winter values was statistically significant (p<0.05). CV values of 48 of the 80 (60%) circadian FEV, time series exceeded the average CV of 5% observed in non-asthmatic children studied in our laboratory. There was an unequal distribution during the year in elevated CV values; 6, 17, 10, and 15 of the high CV values occurred, respectively, in the spring, summer, autumn, and winter. These results suggest that nocturnal bronchial obstruction may change seasonally in terms of severity and amplitude in children who have nearly outgrown their asthma. (Chronobiology International, 13(4), 295–303, 1996)