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.     

Seasonality of births in human populations.

Seasonal fluctuations in births have been observed in virtually all human populations. In this paper we re-examine the seasonality of births with two main objectives in mind. The first is to provide an overview of the basic facts about the seasonality of births, presenting new estimates of the seasonal patterns. Seasonality is an important if not dominant source of nontrend variation in births in virtually all populations, but there are dramatic and puzzling differences across countries and time periods in the pattern of seasonal variation observed in particular populations. The second purpose of the paper is to survey the leading hypotheses about birth seasonality that have appeared in the literature and to discuss the consistency of these hypotheses with observed seasonal patterns. Using our estimates of seasonal patterns along with other evidence in the literature, we conclude that no single explanation receives strong, consistent support from the data.     

Size variation ofAcacia caven (leguminosae) pods along a climatic gradient in Chile

A southward tendency of increment in pod-length is shown for 11 populations ofAcacia caven (Mol.) Hook et Arn. localized along a climatic gradient of increasing annual rainfall in Chile. This fact would suggest thatA. caven populations occurring in the south are in better conditions for reproduction than northern populations, since pod-length is related to the amount of seeds inside the pods. The possible bearing of this southward tendency of increasing seed production upon the expansion ofA. caven toward the more humid zones in southern Chile is discussed.     

Arabidopsis thaliana populations show clinal variation in a climatic gradient associated with altitude

? Understanding the adaptive basis of life history variation is a central goal in evolutionary ecology. The use of model species enables the combination of molecular mechanistic knowledge with ecological and evolutionary questions, but the study of life history variation in natural environments is required to merge these disciplines. ? Here, we tested for clinal variation in life history and associated traits along an environmental and altitudinal gradient in the model species Arabidopsis thaliana. Seventeen natural populations of A. thaliana were geo-referenced in north-eastern Spain on a gradient in which precipitation increases but maximum spring temperature and minimum winter temperature decrease with altitude. ? One hundred and eighty-nine genotypes from the 17 populations were grown under uniform controlled conditions. Variations in traits related to biomass allocation, fecundity, phenology and vegetative growth were tested for relationships with the altitude and climatic variables associated with the home sites. Above-ground mass, number of rosette leaves at bolting, developmental time and seed weight increased with the home site's altitude. Root allocation, vegetative growth during winter and number of seeds decreased with altitude. ? We suggest that the differences among home sites provide clues to the variation in adaptive strategies associated with the climatic gradient. We compared these results with adaptations and clinal relationships reported for other species and with molecular mechanisms described in Arabidopsis.     

Responses of tree populations to climatic change

The influence of climate on the population dynamics of trees must be inferred from indirect sources of information because the long lifespans of trees preclude direct observation of population growth and decline. Important insights about these processes come from 1) observations of the life histories and ecologies of trees in contemporary forests, 2) evidence of recent treeline movements in remote areas unaffected by human disturbance, and 3) results of experiments performed on forest simulation models. Each line of evidence indicates that tree population responses are influenced by many factors: including lifespans, seed productivity and dispersibility, phenotypic plasticity, genetic variability, competition, and disturbance. Some population characteristics should allow rapid changes in population sizes, while others should confer stability in times of environmental fluctuation. Interactions between controlling factors should result in a wide array of possible responses to climatic change. Interpretations of late-Quaternary forest dynamics must be based on an understanding of the biological processes involved in population responses to environmental variations.     

Seasonality of thermophilic Campylobacter populations in chickens

The small intestines and caeca of chickens were monitored for seasonal variation of thermophilic campylobacters over a 12-month period. There was a significant seasonal fluctuation in the carriage rate which correlated with the following environmental parameters: sunshine hours (P = 0.0003) and minimum (P = 0.007) and maximum temperatures (P = 0.003). The number of campylobacters in the small intestine and caeca also showed significant seasonal variation (P = 0.0008); however, the periodicity in the caeca was significantly different from that in the small intestine (P = 0.007). The numbers of Campylobacter in the caeca were significantly higher than those in the small intestine (P = 0.001). No significant correlation was found between the numbers of campylobacters in the caeca and small intestines and the environmental parameters monitored.     

Genetic variation in Echinacea angustifolia along a climatic gradient

BACKGROUNDS AND AIMS: Echinacea angustifolia is a widespread species distributed throughout the Great Plains region of North America. Genetic differentiation among populations was investigated along a 1500 km north-south climatic gradient in North America, a region with no major geographical barriers. The objective of the study was to determine if genetic differentiation of populations could be explained by an isolation-by-distance model or by associations with climatic parameters known to affect plant growth and survival. METHODS: Historical climatic data were used to define the nature of the climatic gradient and AFLP markers were used to establish patterns of population genetic differentiation among ten Echinacea populations collected from North Dakota to Oklahoma. A total of 1290 fragments were scored using six EcoRI/MseI and three PstI/MseI primer combinations. Assessment of the correlation between climatic, genetic and geographic distances was assessed by Mantel and partial Mantel tests. KEY RESULTS: PstI/MseI combinations produced significantly fewer fragments, but a larger percentage was unique compared with EcoRI/MseI markers. Using estimates of F(ST), populations in Oklahoma and southern Kansas were identified as the most divergent from the other populations. Both the neighbour-joining tree and principal co-ordinate analysis clustered the populations in a north-south spatial orientation. About 60% of the genetic variation was found within populations, 20% among populations and the remaining 20% was partitioned among groups that were defined by the topology of the neighbour-joining tree. Significant support was found for the isolation-by-distance model independent of the effects of annual mean precipitation, but not from annual mean temperature and freeze-free days. CONCLUSIONS: Echinacea angustifolia populations exhibit genetic divergence along a north-south climatic gradient. The data support an isolation-by-distance restriction in gene flow that is independent of annual mean precipitation.     

Comparison of enterococcal populations related to urban and hospital wastewater in various climatic and geographic European regions

AIMS: Scarce knowledge about the distribution of enterococci species in wastewaters limits any statement on their reliability as faecal indicators or the implications of antibiotic resistance transmission by these organisms through the water cycle. Enterococci have been involved in nosocomial infections and the spreading of antibiotic resistance through the food chain. The species distribution of enterococci and the presence of resistant strains to vancomycin and erythromycin were analysed in more than 400 raw and treated urban wastewaters, surface waters receiving these treated wastewaters and hospital wastewaters from three European countries. METHODS AND RESULTS: A total of 9296 strains were isolated and biochemically phenotyped. The species identification was based on the comparison of biochemical profiles with those of more than 20000 enterococci isolates from an international study. The prevalence of enterococcal isolates resistant to erythromycin (ERE) and vancomycin (VRE) was also analysed. ERE strains were present in a high proportion in all the studied samples. VRE strains were also isolated in all studied countries despite the time elapsed since the use of antimicrobial glycopeptides in animal production was banned in the European Union. CONCLUSIONS: Enterococcus faecalis and Ent. faecium were the most abundant species in all the studied wastewaters. All the studied wastewaters demonstrated high diversity and similar population structure and composition. ERE and VRE isolates were detected in most of the wastewaters. SIGNIFICANCE AND IMPACT OF THE STUDY: Urban and hospital wastewaters are useful targets for the evaluation of the prevalence of ERE and VRE isolates in the environment. It appears that these bacteria could pass through wastewater treatment plants and be transferred to surface waters.     

Variation in serotiny of three Banksia species along a climatic gradient

The degree of serotiny (i.e. the proportion of follicles remaining closed in each year's crop of cones since the last fire) was measured in Bank-sia attenuata, B. menziesii and B. prionotes at five sites along a climatic gradient extending 500 km north of Perth, Western Australia. The decrease in annual rainfall and increase in average temperature along the gradient paralleled a decrease in plant height and an increase in the degree of serotiny of all species. Extreme serotiny was recorded in the scrub-heath at the xeric end of the gradient whereas two species were essentially non-serotinous in the low woodland at the most mesic site. It is concluded that degree of serotiny is related to the fire characteristics of the site which depend on plant height. In xeric scrub-heath, the entire canopies of the Banksia spp. are consumed by fire which promotes massive release of seed. This facilitates recruitment in an otherwise unpredictable and unreliable seedbed. In mesic woodland, where cones rarely come into contact With flames, seeds are released spontaneously and site conditions are more conducive to recruitment in the inter-fire period.     

Ecotypic differentiation in Medicago polymorpha L. along an environmental gradient in central Chile. II. Winter growth as related to phenology and temperature regime

In this second article of a series analysing ecotypic differentiation ofthe Burr Medic (Medicago polymorpha L.),occurring along a 1000 km natural aridity gradient in centralChile, we report variations in growth potential at low temperature in relationto phenology and latitude of collecting site. In two experiments conducted inoutdoor nursey trials at Cauquenes, in the 'intermediate'(i.e., subhumid) mediterranean zone (35°58 S,72°17 W), biomass accumulation among 4 and 18 accessions ofBurrMedic, was compared. In Experiment 1, the two early-flowering accessionscollected in the arid and semiarid zones (northern Chile) showedsignificantly greater winter growth potential than the twolate-floweringaccessions from humid, south-central Chile, at five different sowingdensities. In Experiment 2, winter growth was compared, at a single sowingdensity, among 18 accessions collected in various sites along the ariditygradient. Here again, growth patterns were closely correlated to latitude ofcollecting site, with early-flowering ecotypes from the north showingsignificantly greater winter growth potential than those from the south. In athird experiment, relative growth rate, net assimilation rate and leaf arearatio and phytomass production were compared among eight accessions grown undertemperature regimes simulating natural growth conditions at Cauquenes in June(winter) and October (spring), i.e.,12°/7°Cand 18°/13°C day/night, respectively. Asbefore, northern accessions showed higher growth potential in the lowertemperature regime than those from humid and perhumid areas at more southernlatitudes. These results suggest that in arid to semiarid environments, whererainfall is erratic and unpredictable, ecotypes of Burr Medic are naturallyselected which show early-flowering and high growth capacity duringwinter, the period of the year when rainfall is most likely to occur inmediterranean-climate regions. Conversely, in humid areas, with higherrainfall predictability, and higher frequency of killing frost, ecotypes havebeen selected with longer periods of growth potential but lower winter growth.Applied and ecological aspects of the results are discussed in the context of along-term program of annual pasture improvement programme.     

Seasonality of mortality in Sri Lanka: Biometeorological considerations

The seasonal variation of mortality in Sri Lanka was studied in relation to meteorological variables. Time series data of the total monthly number of deaths in men and women from 1976 to 1980 were analyzed by power spectrum analysis of the fast Fourier transformation method in the areas of Colombo (lowland area, altitude 7 m) and Nuwara-Eliya (highland area, altitude 1890 m), respectively. In the Colombo area, where the mean temperature was always high (mean, 27.5 °C), a seasonal variation in mortality of 6 months was validated by power spectrum analysis with peak times in June and November. These mortality peaks corresponded to those of the amounts of rainfall which also showed an identical predominant period of 6 months. In the Nuwara Eliya area, where the mean temperature was always low at about 15–16 °C, a seasonal variation of approximately 3 months was found in addition to the 6 months' periodicity. The comparison of the power spectrum pattern of mortality with those of meteorological variables suggested that the amount of rainfall was associated with the seasonal variation of mortality in the Nuwara-Eliya area. In conclusion, the seasonality of mortality in Sri Lanka, a typical tropical zone country, was related to seasonal variation in the amount of rainfall, or a humidity factor, but not to mean temperature.     

Seasonality in water related intestinal disease in Guatemala

Field studies in two rural communities in the Pacific lowlands have been in process since 1973 to evaluate the relationship between environmental improvements, particularly a piped water supply, and the prevalence of diarrheal diseases. An initial appraisal of the data indicates that diarrheal diseases in the tropics vary with the dry and rainy seasons. However, there are aspects of the relationship between water and diarrheal disease which still require explanation. The field studies are designed to provide further insight into these seasonal influences as well as to variations which are related to epidemic cycles, environmental factors and the range of socio-economic development in these areas.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.     

Genetic marker variation in coastal populations of Chile

Gene frequencies for nine genetic marker systems are presented for the following Chilean coastal populations: Paposo, Carelmapu, Laitec and Ukika. Historical and anthropological data suggest the presence of descendants of the Amerindian populations, specifically of Changos, Cuncos, Chonos and Yamanas in these populations. Results indicate that the studied groups maintain an important aboriginal genetic composition. According to Amerindian admixture estimates, the genetic isolation of coastal populations is lower than that of inland populations, suggesting that proximity to the sea facilitated gene flow. Genetic distances and dendrograms were obtained for these populations and another four Chilean Indian populations. Results agree with expectations, taking geographic isolation and non-aboriginal admixture into account.     

Seasonality of mortality: the September phenomenon in Mediterranean countries

Background

Seasonal increases in the mortality rate have been associated with excessively cold or hot weather. We evaluated monthly patterns of mortality in selected countries.

Methods

We analyzed all-cause mortality statistics from 5 European Mediterranean countries (Cyprus, France, Greece, Italy, Spain), Sweden, North America (United States and Canada), Australia, New Zealand and Japan. We extracted and tabulated data on monthly all-cause mortality in the general population from the earliest to the latest year that records were available.

Results

We identified relevant data for a period of 2–57 years in each country. In the Mediterranean countries, the lowest average daily mortality was observed in September (all countries, 125/168 [74%] years). The fewest deaths were in August in Sweden (14/20 [70%] years) and North America (32/50 [64%] years). The fewest deaths in Japan occurred in July (2/2 [100%] years). In the southern hemisphere, the lowest mortality in Australia occurred in March (7/10 [70%] years) and in February for New Zealand (cumulative over 24 years).

Interpretation

Mortality in the general population declines in the late summer to early fall months in the countries evaluated. Environmental parameters may partly account for these associations, and further research is needed on the contribution of additional factors such as summer vacations.Large-scale population studies have shown seasonal variation in mortality rates from various causes in different parts of the world.^1,2 It has been observed that mortality peaks during the cold winter months.³ This observation has led to investigations of the specific causes of death that account for the excess mortality in winter and the underlying pathophysiological mechanisms.^4,5 Human behavioural patterns, socioeconomic factors and environmental parameters are thought to be related to seasonal variations in mortality.^1,3,6 The elucidation of such associations can aid in the organization of relevant public health services.In our practice, we have observed a consistent reduction in the number of patient visits during September for the last 10 years. We hypothesized that morbidity and subsequently mortality is decreased during September in Greece and probably in other countries with similar climatic and socioeconomic conditions.     

Assembly rules of reef corals are flexible along a steep climatic gradient

Coral reefs, one of the world's most complex and vulnerable ecosystems, face an uncertain future in coming decades as they continue to respond to anthropogenic climate change, overfishing, pollution, and other human impacts [1, 2]. Traditionally, marine macroecology is based on presence/absence data from taxonomic checklists or geographic ranges, providing a qualitative overview of spatial shifts in species richness that treats rare and common species equally [3, 4]. As a consequence, regional and long-term shifts in relative abundances of individual taxa are poorly understood. Here we apply a more rigorous quantitative approach to examine large-scale spatial variation in the species composition and abundance of corals on midshelf reefs along the length of Australia's Great Barrier Reef, a biogeographic region where species richness is high and relatively homogeneous [5]. We demonstrate that important functional components of coral assemblages "sample" space differently at 132 sites separated by up to 1740 km, leading to complex latitudinal shifts in patterns of absolute and relative abundance. The flexibility in community composition that we document along latitudinal environmental gradients indicates that climate change is likely to result in a reassortment of coral reef taxa rather than wholesale loss of entire reef ecosystems.     

Soil microbial diversity and community structure across a climatic gradient in western Canada

Soil microbial functional diversity was assessed along a climatic gradient in Western Canada. Mineral soil samples were collected from jack pine (Pinus banksiana Lamb.) stands along an 800km transect between Prince Albert, Saskatchewan and Gillam, Manitoba. Microbial communities were isolated from the soil samples, washed and inoculated into wells of Gram-negative Biolog microplates. Optical density values were used to calculate Shannon diversity indices and to perform principal component analysis. Colour development rank plots (CDR) were created by expressing optical density values as a percentage of total colour development and plotting the wells in descending order. Soil microbial functional diversity decreased with increasing latitude and correlated positively with measures of atmospheric temperature and pH. Soil microbial diversity may be lower in northern sites due to decreased productivity, nutrient limitation and higher acidity. CDR plots are consistent with a trend of increasing environmental harshness moving north along the transect.