Annual rhythm of human reproduction: I. Biology, sociology, or both?

The annual rhythm of human reproduction was analyzed on the basis of more than 3000 years of monthly birth rates covering 166 regions of the globe. The following variables were used to characterize the annual rhythm of human conception (birth minus 9 months): amplitude, phase of maximum and minimum, phase and length of the time span when rates are above the annual mean (alpha), and the steepest upward slope (delta max) of the curve fitted to the rates. The waveform of the annual rhythm is characteristic for geographical regions (e.g., unimodal or bimodal) and persists as such for many years. In most countries, the onset of alpha coincides with delta max and lies close to the spring equinox. This phase of the rhythm is the most stable over time. In many populations, the rhythm has changed in recent years, specifically in amplitude and phase. The phase of the rhythm depends on latitude, with a 6-month difference between the Northern and Southern Hemispheres. The latitudinal distribution of amplitudes is less systematic. In spite of the many social influences on timing of conceptions, we conclude that the seasonal component in human reproduction is based on biological factors.     

Seasonality of conception in human populations in Chile

Seasonality of conceptions in human populations in Chile was studied for a period of 30 years (1945–1974). Clear seasonal conception courses exist in the country, exception made of the northern and southern extremes. Seasonal flux is concentrated mainly in January, but also secondary increases in April and June were observed. Along the 30-year period a general pattern of decreasing seasonality is observed. Conception is significantly related to temperature and photoperiod in this country, the maximum rates of conceptions being observed in coincidence with the maximum temperatures and photoperiods. Nonclimatic factors which may be affecting seasonality of conceptions are also discussed.     

Photoperiod is the main cue that triggers supercooling ability in the land snail, Helix aspersa (Gastropoda: Helicidae).

Helix aspersa hibernates in Brittany (western France), where it may experience subzero temperatures. Studies on cold hardiness, although scarce in land snails, have shown a seasonal variation in supercooling ability, associated with high temperatures of crystallization (Tc). In the present work, two key environmental factors, temperature and photoperiod, were studied to elucidate, how they may affect the enhancement of supercooling ability in the snails from the end of summer to winter. Nine groups of adult snails were acclimated to different combinations of photoperiod (LD-16:8, LD-12:12, and LD-8:16 h) and temperature (15, 10, and 5 degrees C). Temperature of crystallization, hemolymph osmolality, and water content were measured. The results demonstrate a significant effect of the photoperiod on Tc, i.e., shorter photoperiods induce lower Tc (LD-16:8 h, mean Tc = -3.0 degrees C, SD = 2.0; LD-12:12 h, mean Tc = -4.3 degrees C, SD = 1.9; LD-8:16 h, mean Tc = -5.2 degrees C, SD = 1.9; n = 90), whereas the acclimation temperature had no effect. Measurements of hemolymph osmolality and water content showed that osmolality is negatively correlated with water content. Mechanisms such as dehydration are involved in the decrease of Tc. A declining photoperiod triggers a lower Tc, long before the onset of winter conditions. This response may have an adaptive component, allowing individuals to cope with the mild winters typically observed in oceanic regions.     

Contents Volume 34 (2003)

Abstract

Our previous studies indicated that temperature and photoperiod were not involved as temporal variables in effecting the annual changes in human conceptions in the USA. However, temperature still receives attention in the current literature as the important variable in determining the temporal pattern of conceptions. Therefore, we present here a replication of our previous study, involving two additional 11‐year cycles of birth data in the USA, from the interval 1945 thru 1966. The data are transformed to remove linear trends, to remove over‐all mean differences, and to remove differences in amplitude. The data are then clustered into the regional groups determined by the previous study. The replication was obtained when these groups exhibited similar patterns within a 11‐year period and among 11‐year periods. The data from four 11‐year intervals are presented, representing more than 100 million Caucasian births in the USA from 1945 thru 1988. The subtle changes with time are described, and a comparison with a southern hemisphere pattern indicates, along with the other data, that temperature is irrelevant in effecting the annual pattern of changes in conceptions.     

Mountain soils under a changing climate and land-use

Mountain ecosystems are currently experiencing the strongest climatic warming and the largest changes in land-use during the last millennia. The impacts of these changes on soils and their roles in the cycling of carbon and nutrients are, however, largely unknown. Here, we define mountain soils as soils from mountainous areas with cool summers and cold winters and thus, soils from ecosystems that are influenced by snow and ice and where biogeochemical processes are limited by temperature. Because climatic conditions, soil properties, plant species and productivity vary at a small scale in mountains, they provide a unique natural but a seldom used laboratory to study soil processes. In this special issue, we compile different studies on soils from European mountains, reaching from the functioning of mountain soils along natural climatic gradients to responses of greenhouse gas fluxes from mountain soils to experimental warming, soil frost and changes in precipitation.     

Variations of light and temperature regimes and resulting effects on reproductive parameters in medaka (Oryzias latipes).

In seasonally breeding fish species, altered fecundity, fertility, and spawning interval are associated with changes in environmental cues such as temperature and photoperiod. To determine quantitative impact of these cues on a suite of reproductive endpoints, groups of medaka (Oryzias latipes; two breeding pairs per group) were subjected to varying photoperiod and temperature regimes. Embryo production ceased after photoperiod reduction from 16L:8D to 8L:16D (at 25 degrees C). A severe decline in production was observed after a temperature decrease of 10 degrees C (25 degrees C to 15 degrees C [16L:8D]). Under reduced photoperiod, histologic analysis showed no mature ova and moderate oocyte atresia in all individuals. However, reduced temperature (15 degrees C) produced only mild oocyte atresia and fewer mature ova. Under both reduced photoperiod and reduced temperature regimes, mature spermatozoa were observed. Offspring viability, along with spawning interval, were not affected by photoperiod reduction. Temperature change had no effect on offspring viability but caused an increase in spawning interval. A shortened photoperiod profoundly affected medaka reproduction, whereas decreased temperature reduced, but did not arrest, fertility; reduced photoperiod decreased fecundity. These findings have important implications for culture of medaka as well as use of this teleost model for reproductive toxicology studies.     

Increased air temperature during simulated autumn conditions does not increase photosynthetic carbon gain but affects the dissipation of excess energy in seedlings of the evergreen conifer Jack pine

Temperature and daylength act as environmental signals that determine the length of the growing season in boreal evergreen conifers. Climate change might affect the seasonal development of these trees, as they will experience naturally decreasing daylength during autumn, while at the same time warmer air temperature will maintain photosynthesis and respiration. We characterized the down-regulation of photosynthetic gas exchange and the mechanisms involved in the dissipation of energy in Jack pine (Pinus banksiana) in controlled environments during a simulated summer-autumn transition under natural conditions and conditions with altered air temperature and photoperiod. Using a factorial design, we dissected the effects of daylength and temperature. Control plants were grown at either warm summer conditions with 16-h photoperiod and 22 degrees C or conditions representing a cool autumn with 8 h/7 degrees C. To assess the impact of photoperiod and temperature on photosynthesis and energy dissipation, plants were also grown under either cold summer (16-h photoperiod/7 degrees C) or warm autumn conditions (8-h photoperiod/22 degrees C). Photosynthetic gas exchange was affected by both daylength and temperature. Assimilation and respiration rates under warm autumn conditions were only about one-half of the summer values but were similar to values obtained for cold summer and natural autumn treatments. In contrast, photosynthetic efficiency was largely determined by temperature but not by daylength. Plants of different treatments followed different strategies for dissipating excess energy. Whereas in the warm summer treatment safe dissipation of excess energy was facilitated via zeaxanthin, in all other treatments dissipation of excess energy was facilitated predominantly via increased aggregation of the light-harvesting complex of photosystem II. These differences were accompanied by a lower deepoxidation state and larger amounts of beta-carotene in the warm autumn treatment as well as by changes in the abundance of thylakoid membrane proteins compared to the summer condition. We conclude that photoperiod control of dormancy in Jack pine appears to negate any potential for an increased carbon gain associated with higher temperatures during the autumn season.     

Interannual variation in seasonal drivers of soil respiration in a semi-arid Rocky Mountain meadow

Semi-arid ecosystems with annual moisture inputs dominated by snowmelt cover much of the western United States, and a better understanding of their seasonal drivers of soil respiration is needed to predict consequences of climatic change on soil CO₂ efflux. We assessed the relative importance of temperature, moisture, and plant phenology on soil respiration during seasonal shifts between cold, wet winters and hot, dry summers in a Rocky Mountain meadow over 3.5 separate growing seasons. We found a consistent, unique pattern of seasonal hysteresis in the annual relationship between soil respiration and temperature, likely representative for this ecosystem type, and driven by (1) continued increase in soil T after summer senescence of vegetation, and (2) reduced soil respiration during cold, wet periods at the beginning versus end of the growing season. The timing of meadow senescence varied between years with amount of cold season precipitation, but on average occurred 45 days before soil temperature peaked in late-summer. Autumn soil respiration was greatest when substantial autumn precipitation events occurred early. Surface CO₂ efflux was temporarily decoupled from respiratory production during winter 2006/2007, due to effects of winter surface snow and ice on mediating the diffusion of CO₂ from deep soil horizons to the atmosphere. Upon melt of a capping surface ice layer, release of soil-stored CO₂ was determined to be 65 g C, or ~10 % of the total growing season soil respiration for that year. The shift between soil respiration sources arising from moisture-limited spring plant growth and autumn decomposition indicates that annual mineralization of soil carbon will be less dependent on projected changes in temperature than on future variations in amount and timing of precipitation for this site and similar semi-arid ecosystems.     

The influence of seasonal temperatures on the natural regulation of the screw worm, Cochliomyia hominivorax, in the southern U.S.A.

The incidence of screwworm cases in Texas during the 1962-82 sterile-male eradication campaign is analysed in relation to seasonal temperatures and screwworm density. The analysis shows that screwworm outbreaks occur in response to favourable seasonal conditions, especially warm winters and cool summers. The outbreaks collapse following cold winters and hot summers. Screwworm density in autumn also influences rates of increase, possibly through a shortage of wounded hosts in the autumn-winter period. The analysis provides a simple predictive model which not only accounts for the fluctuations in case incidence seen in Texas during the eradication campaign, which others have attributed to strain problems and release methods, but also simulates the historical pattern of screwworm abundance in both Texas and Florida over the last 100 years. It is concluded that screwworm, being essentially a tropical species, might well have been eradicated from the southern U.S.A. by exceptionally unfavourable climate such as occurred in Florida in 1958 and in Texas in the late 1970s and early 1980s. Certainly, unfavourable climate must have been important to the success of the eradication campaigns.     

Thermoregulatory circadian rhythms in the pouched mouse (Saccostomus campestris)

1. Circadian rhythms of body temperature (Tb), oxygen consumption (VO2), and minimal thermal conductance (C) were studied in the pouched mouse, Saccostomus campestris under natural photoperiod during February at a constant ambient temperature of 28 degrees C. 2. Circadian rhythms of body temperature were also studied under natural photoperiod and laboratory temperatures (Max: 28.1 degrees C; Min: 23.2 degrees C) during February. 3. The results of the present study suggest that changes in ambient temperature are not the main "zeitgeber" for body temperature rhythm, and it seems that photoperiod plays a major role in this species. 4. The relationship between the rhythms of Tb, VO2, and C are further discussed.     

Regulation of Activity in Desert-Living Striped Mice: The Importance of Basking

Deserts represent challenging, energy restricted environments for small mammals, but offer ample exposure to sunlight that might be used for energy saving during basking. The Succulent Karoo desert in southern Africa is a seasonal environment with cold moist winters, followed by maximum food availability in spring and dry hot summers with food shortage. The striped mouse (Rhabdomys pumilio) from the Succulent Karoo desert is diurnal and its activity is influenced by photoperiod in captivity. However, in contrast to standardized laboratory conditions, it can be expected that several factors other than photoperiod influence its activity pattern in the field. We expected that striped mice behave in a way that indicates that they use basking to passively warm up and thus reduce endogenous energy expenditure. We studied activity and basking patterns in 56 social groups of striped mice for a period of 4 yr, comprising 1534 observation sessions at their nests. Mice generally started activity around the time the sun illuminated their nest and terminated activity when their nest was no longer sunlit, i.e. they were strictly diurnal. The onset of activity was delayed on days when ambient temperature was colder and when group sizes were smaller. During the breeding season when food availability was high, striped mice usually left the nest before it was sunlit without basking. Outside the breeding season, they emerged and basked in front of nests mainly after nests were sunlit. These findings concur with the view that striped mice trade‐off between active energy gain via foraging and passive energy acquisition by sun basking.     

Plasticity of response of tree-ring width of Scots pine provenances to weather extremes in Latvia

Climatic changes and weather extremes are causing shifts in distribution of tree species, affecting productivity of forests. With the northwards advance of deciduous species in Northern Europe, Scots pine (Pinus sylvestris L.) is predicted to decrease survival and productivity. Nevertheless, Scots pine have adapted to diverse environments, hence selection among its populations could be applied to sustain productivity of stands under changing climate. In this study, sensitivity of tree-ring width of Eastern European provenances of Scots pine differing by field performance (Dippoldiswalde, Eibenstock, Rytel, Gustrow, and Kalsnava) to weather extremes in three trials in Latvia (hemiboreal zone) was assessed via pointer year and tolerance analyses. The studied provenances were sensitive to winter temperature regime; the effects of water deficit and vegetation period’s length were also observed, likely due to warming. The sensitivity of tree-ring width to weather extremes, which differed among the provenances indicating plasticity of growth, correlated with field performance. Although transferred north, the top-performing provenances (Gustrow and Rytel) were able to promptly recover after cold spells as well as dry summers and were able to benefit from warm winters and precipitation-rich summers. The bottom-performing provenances (Dippoldiswalde and Eibenstock) were sensitive to cold spells and summer water deficit, yet were unable to benefit from warm winters, nor moist summers. Considering sensitivity and resilience of growth, the studied top-performing provenances, particularly Rytel, showed commercial potential in the hemiboreal region under warming climate.     

Annual variations in the specific activity of fructose 1,6-bisphosphatase, alanine aminotransferase and pyruvate kinase in the Sparus aurata liver

We determined the annual change in the intermediary metabolism of glucose through the variations of specific activity of fructose 1,6-bisphosphatase (FBPase), alanine aminotransferase (AAT) and pyruvate kinase (PK). Fish (average mass 330 g) were kept in cages under natural conditions of temperature and photoperiod and fed with a commercial diet. FBPase, AAT and PK increased their activity in June in different ways: AAT and PK increased V(max), and FBPase increased the velocity at subsaturating substrate concentrations, changing K(m). The reproduction period modified the annual tendency of changes in the enzyme activities in both parameters, K(m) and V(max), except for K(m) of PK which shows a circa-annual rhythm. No relation between the changes of enzymes activity and photoperiod or temperature has been found in this study, except for K(m) of AAT which presents a positive correlation with photoperiod and a negative correlation with temperature.     

The Effect of Climatic Factors on the Activity Budgets of Barbary Macaques (Macaca sylvanus)

Climatic conditions can significantly affect the behavior of animals and constrain their activity or geographic distribution. Barbary macaques (Macaca sylvanus) are one of the few primates that live outside the tropics. Here we analyze if and how the activity budgets of Barbary macaques are affected by climatic variables, i.e., air temperature, relative humidity, rainfall, and snow coverage. We collected scan sampling data on the activity budgets of four groups of macaques living in the Middle Atlas Mountains of Morocco from June 2008 to January 2011. This habitat is characterized by extreme seasonal changes, from cold and snowy winters to hot and dry summers. The activity budgets of the macaques differed across months but not across the time of day (with the exception of time spent feeding). The monkeys spent significantly more time feeding or foraging when there was no snow than when snow coverage was moderate or major. Daily rainfall was positively related to resting time and negatively to time spent moving or in social behavior. Air temperature was negatively related to time spent feeding or foraging. Finally, time spent on social behavior was significantly lower when relative humidity was high. These data indicate that environmental factors significantly affect the time budgets of endangered Barbary macaques, a species that has been little studied in the wild. Our findings support previous studies on temperate primates in showing that snow coverage can have negative consequences on the feeding ecology and survival of these species.     

Seasonal acclimatization to extreme climatic conditions by black-capped chickadees (Poecile atricapilla) in interior Alaska (64 degrees N).

Winters in interior Alaska (64 degrees N) are characterized by short photoperiod (5L : 19D) and chronic subfreezing temperatures. To determine if seasonal acclimatization of black-capped chickadees (Poecile atricapilla) at high latitude differs from that of conspecifics at lower latitudes, standard metabolic rates (SMR), metabolic response to low temperature (-30 degrees C), nocturnal hypothermia, body mass, fat reserves, and conductance were measured over two winters and one summer in three groups of seasonally acclimatized birds. Body mass and conductance did not vary with season, although furcular fat levels were higher in winter. Birds used nocturnal hypothermia when exposed to -30 degrees C in summer or winter. Although SMR did not vary seasonally, winter SMRs differed between the two winters of the study. Nocturnal hypothermia in summer and decreased SMR in response to extreme conditions may either reflect plasticity inherent to all populations of black-capped chickadees or may result from individual variation within this northern population.     

Photoperiod and temperature can regulate body mass, serum leptin concentration, and uncoupling protein 1 in Brandt's voles (Lasiopodomys brandtii) and Mongolian gerbils (Meriones unguiculatus)

Environmental factors play an important role in the seasonal adaptation of body mass and thermogenesis in wild small mammals. In this study, we performed a factorial experiment (temperature x photoperiod) in which Brandt's voles and Mongolian gerbils were acclimated to different photoperiods (long photoperiod, 16L : 8D; short photoperiod, 8L : 16D) and temperatures (warm, 23 degrees C; cold, 5 degrees C) to test the hypothesis that photoperiod, temperature, or both together can trigger seasonal changes in serum leptin level, body mass, thermogenesis, and energy intake. Our data demonstrate that Brandt's voles showed a remarkable decrease in body mass in both the cold and a short photoperiod. However, no significant changes in body mass were found for gerbils exposed to similar conditions. The short photoperiod induced a decrease in serum leptin levels for both voles and gerbils that might contribute to an increase in energy intake. Furthermore, the short photoperiod induced an increase of uncoupling protein 1 (UCP1) content for both voles and gerbils, and cold can further enhance the increase in voles. No interactions between photoperiod and temperature were detected for the two species. Brandt's voles can decrease their body mass through changes in energy intake and expenditure, while Mongolian gerbils can keep body mass relatively stable by balancing energy metabolism under winterlike conditions. Leptin was potentially involved in the regulation of body mass and thermogenic capacity for the two species.     

The late Pleistocene climates of the Lake Zeribar region (Kurdistan,western Iran) deduced from the ecology and pollen production of nonarboreal vegetation

The concept of an arid pleniglacial in the Middle East depends primarily on the interpretation of pollen diagrams including those of Lake Zeribar in the Zagros Mountains of western Iran. It has been assumed that Lake Zeribar was surrounded by a Chenopodiaceae-Artemisia steppe and that the climate was therefore dry. Both assumptions are questioned. The environment of Pleistocene Lake Zeribar may have been similar to the tragacanthic or alpine zone of the modern Zagros Mountains. The dominance by pollen of Chenopodiaceae and Artemisia is explained by low pollen production of high-altitude vegetation, preferential incorporation of pollen of late-blooming plants into the sediments, and high production and long-distance transport of lowland pollen. In any case, high percentages of Chenopodiaceae and Artemisia pollen do not necessarily indicate low annual precipitation but a highly seasonal climate with cold winters and hot, dry summers. Such a climatic regime was in effect continuous except for a period beginning about 10600 B. P. during which summer rainfall or reduced summer drought occurred. This change in seasonality resulted in the dominance of Poaceae pollen and the initial increase in arboreal pollen. A moisture curve based on the ratio between Chenopodiaceae and Artemisia pollen indicates a pleniglacial climate with wet winters and a late-glacial and early-Holocene climate with periods of intense aridity. The climatic history presented here is compatible with non-palynological evidence of regional late Pleistocene climates and with seasonality changes suggested by climatic modelling based on orbital parameters.Abbreviations C/A Chenopodiaceae-Artemisia ratio     

Survival rates of Redshank Tringa totanus wintering on the Moray Firth

Long-term mark–recapture data were used to estimate the annual survival rates of Redshank wintering on the Moray Firth in Scotland. Survival modelling required the exclusion of all birds caught during the main passage months (August, March and April), and a highly variable annual catching effort limited the precision of annual survival estimates. Survival rates of juvenile Redshank (between the first and second winters of life) varied markedly from year to year and averaged 43% (se 3.6%). Adult survival rates were less variable between years and were age-dependent, with 67% (se 5.0%) surviving and returning between the second and third winters of life, compared to 74% (se 1.4%) for older birds. Year-to-year variation in adult survival was weakly (and negatively) related to the number of snow days in winter. Year-to-year variation in first-year survival was non-linearly related to winter rainfall, with low survival during dry (and cold) winters, higher survival during winters with average rainfall and lower survival during wet winters. Having accounted for these weather relationships there was no evidence that survival was related to the size of the local wintering Redshank population. Organized annual ringing programmes of wintering waders on British estuaries have the potential to monitor long-term changes in survival rates and productivity. Although constant effort sampling may be difficult to achieve for wintering waders, the utility of mark–recapture data collected on estuaries is likely to depend heavily on careful study design.     

Can separation along the temperature niche axis promote coexistence between native and invasive species?

Aim Western mosquitofish (Gambusia affinis) have been linked with the decline of native fish and amphibians throughout the world. Separation along the temperature niche axis may promote the long‐term coexistence of introduced western mosquitofish, with native species in temperate regions. Recent research has shown that western mosquitofish can reduce the recruitment of native least chub (Iothichthys phlegethontis) endemic to the Bonneville Basin. We tested the hypotheses that cold temperatures (≤ 15 °C in the summer, freezing winters) would: (1) reduce the aggressive and predatory effects of western mosquitofish on least chub, and (2) eliminate the overwinter survival and recruitment of western mosquitofish while having little effect on least chub recruitment. Location Bonneville Basin of Utah, USA. Methods We used short‐term tests in the laboratory at the level of individuals and manipulated temperature (warm, cold and seasonal treatments) in long‐term experiments using mesocosms at the population level. Results Cold temperatures (≤ 15 °C) reduced the aggression and predation of western mosquitofish on least chub at the level of individuals. At the population level, however, cool summers (≤ 15 °C) eliminated recruitment in both species because they required warm summers (c. 20–30 °C) to survive freezing winters. Although least chub had an overwinter advantage in survival (75% least chub, 45% western mosquitofish), it was overwhelmed by the rapid reproduction of western mosquitofish as temperatures increased in the summer. Main conclusions Studies at the level of populations are necessary to understand the ultimate effects of introduced species on native taxa. Separation along the temperature niche axis was not sufficient to promote coexistence between these species in habitats with warm summers (c. 30 °C). Although coexistence may be possible in habitats with cool summers (≤ 20 °C) and freezing winters, the ability of niche separation to promote long‐term coexistence between native and introduced species may ultimately depend on their respective rates of evolution. Long‐term coexistence may not be possible if introduced species can adapt to new environmental conditions faster than native species can evolve mechanisms to reduce their harmful effects.     

Flying in the face of climate change: a review of climate change, past, present and future

The distribution and abundance of birds is known to depend critically upon climate variability at a range of temporal and spatial scales. In this paper we review historical changes in climate in the context of what is known about climate variability over the last millennium, with particular reference to the British Isles. The climate of Britain is now warmer than it has been in at least 340 years, with the 1990s decade 0.5 °C warmer than the 1961–1990 average. In addition, the frequency of cold days (mean temperature below 0 °C), particularly during March and November, has declined and there has been a marked shift in the seasonality of precipitation, with winters becoming substantially wetter and summers becoming slightly drier. Current understanding is that the rate of future warming is likely to accelerate with more frequent and more intense summer heatwaves, milder winters, an increase in winter rainfall, an increased risk of winter river floods, and an increase in mean sea-level and associated coastal flooding. All of these aspects of climate change are likely to impact on coastal birds. A range of potential future climate scenarios for the British Isles are presented derived from recently completed global climate model experiments. For migrant bird species, changes in the British climate have also to be seen within the context of remote climate change in both the breeding and the overwintering grounds.