Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEASONS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
PubMed2006

Seasonal variation of estradiol, follicle stimulating hormone, and dehydroepiandrosterone sulfate in women and men.

CONTEXT: Seasonal variation in daylight regulates reproduction in animals living at higher latitude, but the influence of season on the sex hormones in humans remains unclear. OBJECTIVE, DESIGN, AND PARTICIPANTS: A cross-sectional population-based study in Tromsø, Norway (70 degrees N) included 1651 women and 1540 men aged 25-84 yr. Circulating total estradiol (and calculated free levels), FSH, and dehydroepiandrosterone sulfate (DHEAS) were measured between September 1994 and September 1995 and provided a unique opportunity to study effects of extreme seasonal variations in the daylight on hormone levels in an arctic population. MAIN OUTCOME MEASURE: Circulating total and free estradiol, FSH, and DHEAS were measured. RESULTS: Total and free estradiol showed differences between monthly means, with peak in June in postmenopausal women (P < 0.001), and in May in men (P = 0.002 and P < 0.001) by analysis of covariance. By cosinor analysis, a seasonal variation in total and free estradiol was evident in women (P = 0.02 and P = 0.03) and men (P = 0.004 and P = 0.001), but only 0.2-0.9% of the variation in total and free estradiol was explained by season. FSH and DHEAS showed no obvious seasonal variation in either sex. CONCLUSIONS: Seasonal variations should be considered while designing studies and interpreting results of estradiol measurements to avoid bias in comparative studies.

Adult↗
PubMed2002

Seasonal changes in calciotropic hormones, bone markers, and bone mineral density in elderly women.

Seasonal variation of serum vitamin D metabolites, PTH, bone turnover markers, and bone mineral density (BMD), adjusted for confounding variables, was studied in a cross-sectional population of 251 ambulatory elderly women aged 65-77 yr. A significant (P < 0.05) seasonal change was observed in serum 25 hydroxyvitamin D (25OHD), bone resorption marker (urine N-telopeptide), and BMD of the spine, total body, and mid-radius. Serum 25OHD was significantly lower (P < 0.05) in winter (December, January, February, March) compared with summer (June, July, August, September), with the nadir in February (68.4 +/- 6.74 nmol/liter) and the zenith in August (85.6 +/- 5.12 nmol/liter). Mean serum PTH levels were higher in winter when serum 25OHD was low, and mean serum PTH was lower in summer when serum 25OHD was high, although the seasonal change in serum PTH was not significant. The change in serum 1,25-dihydroxy vitamin D(3) paralleled that of serum 25OHD levels, but the seasonal effect was not significant. Mean 24-h urine N-telopeptide showed a significant seasonal change (P < 0.05); it was about 24% higher in February (zenith) compared with that in August (nadir). The zenith month of urine N-telopeptide levels corresponded to the nadir month of serum 25OHD levels and vice versa. A significant (P < 0.05) inverse correlation was observed between 24-h urine N-telopeptides and serum 25OHD levels. There was a significant (P < 0.05) seasonal change in mean BMD of spine, total body, and mid-radius. These changes paralleled those in serum 25OHD levels. Spine BMD was 8.4% higher in August (zenith) compared with that in February (nadir), whereas total body BMD and mid-radius BMD were 6.1 and 7.6% higher, respectively, in July (zenith) compared with that in January (nadir). There was a nonsignificant increase of 3.6% in total hip BMD. In summary (see Fig. 5), the seasonal changes in vitamin D metabolism in elderly women are closely associated with small changes in serum PTH, changes in bone resorption, and BMD.

Absorption↗
PubMed2003

Seasonal acclimatisation of muscle metabolic enzymes in a reptile (Alligator mississippiensis).

Reptiles living in heterogeneous thermal environments are often thought to show behavioural thermoregulation or to become inactive when environmental conditions prevent the achievement of preferred body temperatures. By contrast, thermally homogeneous environments preclude behavioural thermoregulation, and ectotherms inhabiting these environments (particularly fish in which branchial respiration requires body temperature to follow water temperature) modify their biochemical capacities in response to long-term seasonal temperature fluctuations. Reptiles may also be active at seasonally varying body temperatures and could, therefore, gain selective advantages from regulating biochemical capacities. Hence, we tested the hypothesis that a reptile (the American alligator Alligator mississippiensis) that experiences pronounced seasonal fluctuations in body temperature will show seasonal acclimatisation in the activity of its metabolic enzymes. We measured body temperatures of alligators in the wild in winter and summer (N=7 alligators in each season), and we collected muscle samples from wild alligators (N=31 in each season) for analysis of metabolic enzyme activity (lactate dehydrogenase, citrate synthase and cytochrome c oxidase). There were significant differences in mean daily body temperatures between winter (15.66+/-0.43 degrees C; mean +/- S.E.M.) and summer (29.34+/-0.21 degrees C), and daily body temperatures fluctuated significantly more in winter compared with summer. Alligators compensated for lower winter temperatures by increasing enzyme activities, and the activities of cytochrome c oxidase and lactate dehydrogenase were significantly greater in winter compared with summer at all assay temperatures. The activity of citrate synthase was significantly greater in the winter samples at the winter body temperature (15 degrees C) but not at the summer body temperature (30 degrees C). The thermal sensitivity (Q(10)) of mitochondrial enzymes decreased significantly in winter compared with in summer. The activity of mitochondrial enzymes was significantly greater in males than in females, but there were no differences between sexes for lactate dehydrogenase activity. The differences between sexes could be the result of the sex-specific seasonal demands for locomotor performance. Our data indicate that biochemical acclimatisation is important in thermoregulation of reptiles and that it is not sufficient to base conclusions about their thermoregulatory ability entirely on behavioural patterns.

Acclimatization↗
PubMed2005

Muscle remodeling in relation to blood supply: implications for seasonal changes in mitochondrial enzymes.

We investigated if seasonal changes in rainbow trout muscle energetics arise in response to seasonal changes in erythrocyte properties. We assessed if skeletal muscle mitochondrial enzymes changed (1) acutely in response to changes in erythrocyte abundance, or (2) seasonally when we altered the age profile of erythrocytes. Rainbow trout were treated with pheynylhydrazine, causing a 75% reduction in hematocrit within 4 days. After erythropoiesis had returned hematocrit to normal, treated and control fish were subjected to a seasonal cold acclimation regime to assess the impact of erythrocyte age on skeletal muscle remodeling. Anemia (i.e. phenylhydrazine treatment) did not alter the specific activities (U g(-1) tissue) of mitochondrial enzymes in white or red muscle. Anemic pretreatment did not alter the normal pattern of cold-induced mitochondrial proliferation in skeletal muscle, suggesting erythrocyte age was not an important influence on seasonal remodeling of muscle. Anemia and cold acclimation both induced a 25-30% increase in relative ventricular mass. The increase in relative ventricular mass with phenylhydrazine treatment was accompanied by a 35% increase in DNA content (mg DNA per ventricle), suggesting an increase in number of cells. In contrast, the increase in ventricular mass with cold temperature acclimation occurred without a change in DNA content (mg DNA per ventricle), suggesting an increase in cell size. Despite the major increases in relative ventricular mass, neither anemia nor seasonal acclimation had a major influence on the specific activities of a suite of mitochondrial enzymes in heart. Collectively, these studies argue against a role for erythrocyte dynamics in seasonal adaptive remodeling of skeletal muscle energetics.

Acclimatization↗
PubMed2003

Seasonal changes in spermatogenesis and testicular steroidogenesis in wild male raccoon dogs (Nyctereutes procynoides).

Testes of 15 wild adult male raccoon dogs (Nyctereutes procynoides) obtained from September 2000 to April 2001 were studied to clarify seasonal changes in spermatogenesis and testicular steroidogenesis. There were marked seasonal variations in the testis weight and size with values relatively low in September and highest in March. Spermatogonia and primary spermatocytes were observed in September, while spermatogonia, spermatocytes and round spermatids were present in January, and all types of spermatogenic cells including mature spermatozoa were found in the mating season (February and March). The number of spermatogenic cells reached their peak values in February and March. In addition, steroidogenic enzymes were immunolocalized using polyclonal antisera raised against bovine adrenal cholesterol side-chain cleavage cytochrome P450 (P450scc), human placental 3beta-hydroxysteroid dehydrogenase (3 betaHSD), porcine testicular 17alpha-hydroxylase cytochrome P450 (P450c17), and human placental aromatase cytochrome P450 (P450arom). P450scc and P450c17 were identified in Leydig cells and spermatids in February, whereas these enzymes were present only in Leydig cells in September. 3betaHSD was found in Leydig cells in September and February with more intense staining in February. The localization of P450arom changed seasonally: no immunostaining in September; more extensive immunostaining in Leydig cells, Sertoli cells, and elongating spermatids in February. These results suggest that seasonal changes in the testis weight and size of wild male raccoon dogs are correlated with changes in spermatogenesis. Seasonal changes in testicular steroidogenesis suggest that the synthesis of androgen and estrogen reaches its peak in the mating season.

Animals↗
PubMed2006

Season of birth and childhood intelligence: findings from the Aberdeen Children of the 1950s cohort study.

BACKGROUND: In this study, 2 main hypotheses have been put forward to explain the variation in childhood intelligence or school performance by season of birth. In the first hypothesis, it is suggested that it is due to school policy concerning school entry, whereas the second suggests that a seasonally patterned exposure such as temperature, maternal nutrition, or infection during critical periods of brain development have a lasting effect on intelligence. AIMS: To determine whether childhood performance on tests of different domains of intelligence is patterned by season of birth and to examine possible mechanisms for any associations. SAMPLE: 12,150 individuals born in Aberdeen, Scotland between 1950 and 1956. METHODS: Birth cohort study in which the variation in different domains of childhood intelligence measured at ages 7, 9, and 11 by season of birth were examined. RESULTS: Reading ability at age 9 and arithmetic ability at age 11 varied by season of birth, with lowest scores among those born in autumn or early winter (September-December) and highest scores among those born in later winter or spring (February-April); p=.002 for joint sine-cosine functions for reading ability at age 9 and p=.05 for sine-cosine function for arithmetic ability at age 11. The child's perception and understanding of pictorial differences at age 7, verbal reasoning at 11, and English language ability at 11 did not vary by season of birth. Age at starting primary school and age relative to class peers were both associated with the different measurements of childhood intelligence and both attenuated the association between month of birth and reading ability at age 9 and arithmetic ability at age 11 towards the null. Both adjusted and unadjusted differences in reading ability at age 9 and arithmetic ability at age 11 between those born from September to December compared with other times of the year were less than 0.1 of a standard deviation of the test scores. Ambient temperature around the time of conception, during gestation, and around the time of birth did not affect intelligence. CONCLUSION: Any variation in mean childhood intelligence by season of birth is weak and largely explained by age at school entry and age relative to class peers.

Achievement↗
PubMed2004

Seasonal variation of genotype-specific fertility and adaptation to endemic diseases: a study in past malarial areas of Italy.

Cyclic seasonal variation of genotype-specific fertility could interact with endemic diseases characterized by seasonal variation of severity resulting in changes of gene frequencies in the course of generations. Assuming that a given allele A has a frequency pw in infants conceived in the cold season and a frequency of ps in those conceived in the warm season and assuming that general fertility is the same in the two seasonal periods, the gene frequency in the population is pm = (pw + ps)/2; this frequency remains constant over the course of generations. The introduction of an endemic disease bearing negatively on general fertility and characterized by a seasonal pattern of severity could result in variations of the A allele frequency. If the maximum of endemicity coincides with the maximum value of the allele A frequency, the frequency of allele A will progressively decrease. A simple mathematical algorithm has been applied to two polymorphic enzymes (ACP1 and G6PD) correlated with past malarial morbidity in Sardinia and the Po River delta. The two systems show differences in gene frequency in relation to season of conception. The theoretical changes fit quite well with the data observed in Sardinian and Po delta populations, thus suggesting a mechanism that is an alternative to or concurrent with the classical mechanism that assumes a direct connection between the genetic systems and the biology of the malarial parasite.

Adaptation, Physiological↗
PubMed2004

Supplementation with oral vitamin D3 and calcium during winter prevents seasonal bone loss: a randomized controlled open-label prospective trial.

UNLABELLED: Bone metabolism follows a seasonal pattern with high bone turnover and bone loss during the winter. In a randomized, open-label 2-year sequential follow-up study of 55 healthy adults, we found that supplementation with oral vitamin D3 and calcium during winter abolished seasonal changes in calciotropic hormones and markers of bone turnover and led to an increase in BMD. Supplementation with oral vitamin D3 and calcium during the winter months seems to counteract the effects of seasonal changes in vitamin D and thus may be beneficial as a primary prevention strategy for age-related bone loss. INTRODUCTION: Bone metabolism follows a seasonal pattern characterized by high bone turnover and bone loss during winter. We investigated whether wintertime supplementation with oral vitamin D3 and calcium had beneficial effects on the circannual changes in bone turnover and bone mass. MATERIALS AND METHODS: This prospective study comprised an initial observation period of 12 months ("year 1"), followed by an intervention during parts of year 2. Fifty-five healthy subjects living in southwestern Germany (latitude, 49.5 degrees N) were randomized into two groups: 30 subjects were assigned to the treatment group and received oral cholecalciferol (500 IU/day) and calcium (500 mg/day) during the winter months of year 2 (October-April), while 25 subjects assigned to the control group obtained no supplements. Primary endpoints were changes in calciotropic hormones [serum 25(OH)D, 1,25(OH)2D, and parathyroid hormone], markers of bone formation (serum bone-specific alkaline phosphatase) and of bone resorption (urinary pyridinoline and deoxypyridinoline), and changes in lumbar spine and femoral neck BMD. RESULTS: Forty-three subjects completed the study. During year 1, calciotropic hormones, markers of bone turnover, and BMD varied by season in both groups. During the winter months of year 1, bone turnover was significantly accelerated, and lumbar spine and femoral BMD declined by 0.3-0.9%. In year 2, seasonal changes in calciotropic hormones and markers of bone turnover were either reversed or abolished in the intervention group while unchanged in the control cohort. In the subjects receiving oral vitamin D3 and calcium, lumbar and femoral BMD increased significantly (lumbar spine: +0.8%, p = 0.04 versus year 1; femoral neck: +0.1%, p = 0.05 versus year 1), whereas controls continued to lose bone (intervention group versus control group: lumbar spine, p = 0.03; femoral neck, p = 0.05). CONCLUSIONS: Supplementation with oral vitamin D3 and calcium during winter prevents seasonal changes in bone turnover and bone loss in healthy adults. It seems conceivable that annually recurring cycles of low vitamin D and mild secondary hyperparathyroidism during the winter months contributes, at least in part and over many years, to age-related bone loss. Supplementation with low-dose oral vitamin D3 and calcium during winter may be an efficient and inexpensive strategy for the primary prevention of bone loss in northern latitudes.

Absorptiometry, Photon↗
PubMedDate not supplied

Seasonal variation in diagnoses and visits to family physicians.

BACKGROUND: Practice-based research networks (PBRNs) replicating the National Ambulatory Medical Care Survey (NAMCS) must sample more than 1 year to account for presumed seasonal variation in illnesses. This study evaluated the effects of seasonality on diagnoses within NAMCS family physician data. METHODS: Using combined data from the 1995-1998 NAMCS, diagnostic clusters that accounted for more than 1% of total visits were analyzed for seasonality. Seasons were coded categorically as dummy variables with summer as the reference category. A logistic regression was performed with each diagnosis as an outcome on the full data. To examine the ability of alternative sampling strategies to replicate the full year of data, a simulation study was carried out drawing 50 samples of 1,000 visits each for winter-summer and spring-fall sampling periods. RESULTS: We found 23 diagnostic clusters that had a frequency more than 1%, of which 10 had seasonal variations (P < or = .001), primarily between winter and summer. If sampling were restricted to spring, the diagnostic clusters of pregnancy and coronary artery disease would account for less than 1% of visits. All other diagnostic clusters, though changing rank order, would account for more than 1% if sampled in a single quarter. In the simulated sampling strategy, visit prevalence dropped below 1% for at least 1 diagnosis in 24 of 50 samples in spring-fall compared with 20 of 50 samples for winter-summer (P > .20). CONCLUSIONS: There is little seasonal variation in the 23 diagnoses that occur in more than 1% of visits to family physicians. There is, however, important seasonal variation in the rank order of these diagnoses. A sampling strategy that uses any quarter of the year but spring (March, April, May) could be used to understand what diagnoses are frequently seen within a PBRN.

Adult↗
PubMed1999

Statistical analysis of the seasonal variation in the twinning rate.

There have been few secular analyses of the seasonal variation in human twinning and the results are conflicting. One reason for this is that the seasonal pattern of twinning varies in different populations and at different periods. Another reason is that the statistical methods used are different. The changing pattern of seasonal variation in twinning rates and total maternities in Denmark was traced for three periods (1855-69, 1870-94, and 1937-84). Two alternative methods of analysis are considered. The method of Walter and Elwood and a trigonometric regression model give closely similar results. The seasonal distribution of twin maternities for the periods in the 19th century showed highly significant departures. For both twin and general maternities, the main peaks can be seen from March to June and a local peak in September. During the spring-summer season the twinning rates were higher than the total birth rates, indicating a stronger seasonal variation for the twin maternities than for the general maternities. For 1937-84, there was a similar, but less accentuated, pattern. Studies of other populations are compared with the Danish results. The more accentuated seasonal variation of twinning in the past indicate that some factors in the past affected women during summer-autumn and around Christmas time, making them more fecund and particularly to be more prone to polyovulation and/or more able to complete a gestation with multiple embryos.

Birth Rate↗
PubMed2004

Effects of seasonal and physiological variations on the serum major and trace element levels in sheep.

The aim of this study was to investigate the possible effects of the seasonal and physiological variations on the Cu, Zn, Mg, Fe, Se, Ca, K, Na, Cl, and P concentrations and their relationships with the estradiol and progesterone levels in Sakiz-Ivesi sheep. For this purpose, 34 healthy Sakiz-Ivesi crossbreed sheep were divided into two groups. The first group (n=22) was mated and the second group (n=12) was not mated. They were raised under pasture conditions and without any dietary supplementation. Their serum samples were collected four times a year at each season and under each physiologic condition. The periods are 1=early pregnancy (October), 2=late pregnancy (January), 3=lactation (April), and 4=dry season (July). The results of this study indicated that (1) Mg concentrations in serum vary with seasonal variations but not physiological variations, (2) Fe and K concentrations in serum vary only with physiological variations, (3) the Cu concentration changes not only pregnancy but also through some other hormonal changes not caused by pregnancy, (4) Ca, P, and Se concentrations could vary with both physiologic and seasonal variations, (5) Zn, Na, and Cl were almost identical for both groups and altered depending on neither season of the year nor the physiologic status, (6) both increased estradiol level and increased progesterone level can raise Cu levels in serum, and (7) increased serum Ca concentrations are related with increased estradiol and decreased P and Mg levels. These observations suggest that seasonal and physiologic variations and sexual cycle have to be taken into consideration for a correct interpretation of elements status. If sheep are maintained at pasture conditions, the nutritional requirements must be supplemented during certain periods. Otherwise, it is apparent that this will cause a decline in the total performance of sheep and, consequently, economic lost.

Animals↗
PubMed2000

Selenium, copper, and zinc indices of nutritional status: influence of sex and season on reference values.

The objective was to estimate the possible influence of season or season and sex on the selenium, glutathione peroxidase (GSH-Px), copper, zinc, and superoxide dismutase (SOD) values in plasma with a view to establishing reference values. For this purpose, 55 healthy volunteers (36 women and 19 men) were selected and their whole-blood samples were collected four times a year at the beginning of each season. In the population as a whole, no statistically significant seasonal differences were detected in copper, selenium, and GSH-Px values in plasma, whereas zinc and SOD values in plasma depended on the season. In general, the variability was higher among the women. In view of the differences detected according to sex and/or season in the parameters studied, we recommend taking samples from men and women and from different seasons to establish reference values.

Copper↗
PubMed2002

Use of statistical techniques in studies of suicide seasonality, 1970 to 1997.

The effect of seasons on suicides has been suggested repeatedly. In order to reveal a true seasonal pattern, an appropriate statistical technique, which is sensitive to a specific type of cyclic variation in the data, must be chosen. This study is a review of the use of statistical techniques for seasonality and of some important characteristics of study samples that were evaluated from 46 original suicide seasonality articles published in major psychiatric journals. The results showed that statistical techniques were applied in a majority of articles, but they were commonly lacking regarding analyses, which compared seasonal patterns among subgroups of a population. In recent studies more sophisticated statistical techniques were utilized for seasonality, like spectral analyses, as compared with earlier studies, in which the emphasis was on chi-square tests. Lack of reporting essential features of the data, such as the sample size and monthly values of suicides, were frequent. The calendar effect was adjusted only in 11 studies. Some recommendations concerning the methodological and reporting issues are summarized for future articles on the seasonal affect on suicides.

Bias↗
PubMed1993

Seasonal fluctuation in diurnal rhythms of luteinizing hormone secretion in ewes during the mid-luteal phase of the oestrous cycle.

Diurnal and seasonal fluctuations were detected in luteinizing hormone (LH) interpulse interval, but not amplitude, in ewes examined during the mid-luteal phase of an oestrous cycle at five stages of the breeding season. Daytime and night-time LH interpulse intervals were greater in the early and late than in the mid-breeding season (P < 0.05). During the early and late breeding season, LH interpulse interval was less during daylight than during darkness (P < 0.05). Toward the mid-breeding season, interpulse interval decreased during daytime earlier in the season than the night-time decrease. It was concluded that the diurnal fluctuations observed are a component of a circannual rhythm in LH secretion resulting from gradual seasonal transitions in photoperiodic drive to, or an endogenous rhythm in, the hypothalamic-pituitary axis in ewes.

Animals↗
PubMed1993

[Hypothalamo-pituitary-ovarian function in female Japanese monkeys (Macaca fuscata) in the non-mating season].

We investigated the mechanism of reduction of hypothalamo-pituitary-ovarian function in female Japanese monkeys in the non-mating season. We administered PMSG and LH-RH to 19 females in the non-mating and in the mating season. When PMSG was administered every day for 12 to 14 days to seven monkeys in the non-mating season, follicle development was observed together with an increase in serum estradiol-17 beta (E2), but there was no rise in serum LH in two animals and little increase in five others. Follicle involution began about ten days after PMSG administration, and no ovulation occurred. These findings show that secretion of LH by the pituitary in response to positive feedback by the E2 secreted by the follicles which had developed was in adequate to induce ovulation. Serum LH levels increased markedly in five females after a single iv injection of LH-RH in the mating season, but not at all in the non-mating season, even when five-times the dose was administered. These data show that the LH-secreting function of the pituitary is definitely reduced in the non-mating season. When LH-RH was administered to seven monkeys following PMSG administration, an LH surge was observed in all animals, and ovulation occurred in four animals. These findings suggest that one reason for the reduction in pituitary-ovarian function in the non-mating season was a decline in LH-RH secretion by the hypothalamus.

Animals↗
PubMed2001

Morphometric comparison of Simulium perflavum larvae (Diptera: Simuliidae) in relation to season and gender in Central Amazônia, Brazil.

Number of larval instars, age structure and environmental effects on these parameters represent basic information in the study of insect population biology. When species have economic importance, this information is essential in order to choose the best period to apply different control methods and to determine the stages of the life cycle of the insect that are most susceptible to each treatment. The family Simuliidae has many species of medical/veterinary importance in the world, and some studies in the temperate region have suggested that the number of larval instars and the larval size can vary according to the season, gender and some environmental factors, such as temperature and diet. This study, with the zoophilic species Simulium perflavum Roubaud, is the first in the Neotropics observing some of these factors and will serve as a template for other species of medical importance in the region. S. perflavum larvae were collected in five streams in Central Amazônia (Manaus and Presidente Figueiredo counties, State of Amazonas), in Sept./Oct. 1996 (dry season) and Feb./Mar. 1997 (rainy season). These larvae were measured (lateral length of head capsule and width of cephalic apodema) to determine the number of larval instars (n=3985), to compare the larval size between seasons and genders (last and penultimate larval instars, n=200). Seven larval instars were determined for this species using frequency distributions, t-tests and Crosbýs growth rule. Significant differences were not detected (t-test, p>0.05) in larval size between seasons and genders. Our results differ from some found in temperate regions suggesting that in the Neotropical region the larval size in different seasons and different genders remains constant, although some environmental parameters, such as diet, change depending on the season.

Animals↗
PubMed2000

Seasonal abundance of Anopheles farauti (Diptera: Culicidae) sibling species in far north Queensland, Australia.

In the Cairns area of far north Queensland, Australia, the seasonal abundance of Anopheles farauti Laveran sibling species was studied at 6 locations, representing 3 habitat types, between August 1995 and September 1997. A total of 45,401 An. farauti s.l. was collected using CO2 + octenol baited CDC light traps, and consisted of 29,565 An. farauti No. 2, 14,214 An. farauti No. 3, and 1,622 An. farauti s.s. The relative abundance of all 3 species differed significantly by season and location. An. farauti No.2 was the dominant species except in Cairns, where An. farauti s.s. was most abundant, and at Ninds Creek, where An. farauti No. 3 predominated. The dominant species at each location was present year round, although peaks in seasonal abundance were observed. An. farauti s.s. populations were highest during the wet season (January-April). In lowland freshwater swamp habitats and 1 brackish location, An. farauti No. 2 was more abundant during the wet season. However, at the highland freshwater swamp habitat, populations of An. farauti No. 2 were highest during the late dry season and early wet season (October-December). There was a significant positive correlation of both temperature and rainfall with An. farauti s.s. and An. farauti No. 2 trap collections. There was a negative correlation between An. farauti No. 3 and temperature, indicating that this species may be more abundant during cool weather. Although there were significant relationships among weather variables and An. farauti s.l. collections, correlation values were generally low, indicating that other factors may contribute to variability among An. farauti sibling species trap collections.

Analysis of Variance↗
PubMed1981

Importance of variations in behavioural and feedback actions of oestradiol to the control of seasonal breeding in the ewe.

Seasonal variations in the behavioural and feedback actions of oestradiol in the ewe were examined by determining the ability of various physiological oestradiol concentrations to elicit oestrous behaviour, induce an LH surge, and suppress tonic LH secretion at four times of the year. These tests were performed in acutely ovariectomized animals pretreated with oestradiol and progesterone to minimize seasonal differences in their endocrine status. Although smaller amplitude LH surges were observed in anoestrus, the dose-response curves for the induction of LH surges were virtually identical at all times of the year. Oestradiol was slightly less effective in eliciting oestrous behaviour in anoestrus and during the transition to the breeding season than at other times. This seasonal variation was, however, observed only with relatively low oestradiol concentrations; serum oestradiol levels of 3 pg/ml or greater induced oestrus in almost all ewes regardless of season. In contrast, there was a marked seasonal change in the negative feedback action of oestradiol. In anoestrus, basal oestradiol levels of 1-3 pg/ml suppressed LH to low levels (0.3 ng/ml), whereas in the breeding season, even peak oestradiol concentrations of 10 pg/ml were not able to produce this degree of inhibition. These results thus support the hypothesis that the annual breeding cycle of the ewe is governed primarily by shifts in the extent to which oestradiol can suppress tonic LH secretion.

Animals↗