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Seasonal Level (seasonal + level)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

SEASONAL CYCLES OF ALLOZYME-BY-CHROMOSOMAL-INVERSION GAMETIC DISEQUILIBRIUM IN DROSOPHILA SUBOBSCURA

EVOLUTION, Issue 4 2003
Francisco Rodríguez-Trelles
Abstract Allozyme loci are frequently found non randomly associated to the chromosomal inversions in which they are included in Drosophila. Two opposite views compete to explain strong allozyme-by-inversion gametic disequilibria: they result from natural selection or, conversely, merely represent remnants of associations accidentally established at the origin of inversions. Empirical efforts aimed at deciding between adaptive and historical scenarios have focused on the spatial distribution of disequilibria. Yet, the evolutionary significance of these associations remains uncertain. I report here the results of a time-series analysis of the seasonal variation of alleles at six allozyme loci (Acph, Lap, Pept-1, Ao, Mpi, and Xdh) in connection with the O chromosomal polymorphisms of D. subobscura. The findings were: (1) in the segment I of the O chromosome, Lap and Pept-1 allozymes changed seasonally in a cyclical fashion within the ST gene arrangement, but they changed erratically within the 3+4 gene configuration; (2) the frequencies of Lap111 and Pept-10,40 within ST dropped to their lowest values in early and late summer, respectively, when the seasonal level of the ST arrangement is lowest. Furthermore, Lap1,11 and Pept-10,40 covary with ST only within these seasons, yet in a fashion inconsistent with these alleles having a major influence on the dynamics of the inversion; (3) seasonal cycling of alleles within inversions were not detected at Acph, Ao, Mpi, and Xdh, yet these loci are nearly monomorphic at the study population, and/or their sampled series were shorter than those for Lap and Pept-1; and (4) simply monitoring allozyme frequencies separately for each inversion proved to be superior, for evidencing the seasonal cycles of the disequilibria, to the use of the D' coefficient of association. Observed seasonal cycles of allozymes within inversions likely reflect natural selection. [source]

Interactions between fishing strategies of Nephrops trawlers in the Bay of Biscay and Norway lobster diel activity patterns

FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2008
V. M. TRENKEL
Abstract, Norway lobster, Nephrops norvegicus (L.), in the Bay of Biscay exhibited diel activity patterns with more individuals outside their burrows at dawn and dusk, increasing catchability at these times. Data from an on board observer programme on Nephrops trawlers between 2002 and 2005 were used to assess variability in catchability in commercial catches. Catch numbers per haul varied spatially and between months, but no signal for diel variations was found. Fishing strategies developed by the Nephrops trawlers had several components. On a seasonal level, they started around sunrise. On a haul level, haul duration decreased from haul to haul, with the longest hauls taking place at the time of the highest catchability. By-catch of hake, Merluccius merluccius (L.), increased more than proportionally with haul duration. [source]

Surface air temperature trends in Southern Brazil for 1960,2002

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008
Jose A. Marengo
Abstract Trends in minimum and maximum air temperature and in the diurnal thermal range (DTR), and derived indices of extreme temperatures since the 1960's are assessed for southern Brazil. Most meteorological stations show steep increases in the night-time temperatures (depicted by the minimum temperature) as compared to slight increases in the daytime temperature (depicted by the maximum temperature), both year round and at the seasonal level. The warming trends are stronger during winter as compared to summer. Consequently, the observed annual and seasonal negative DTR trends in southern Brazil during the last 40 years are largely due to the greater increase in nighttime temperatures rather than daytime temperatures. At decadal timescales, the presence of more intense and frequent El Niño events during the last 20 years also contributes to warming and explains the steep increase in the air temperature extremes trends during this period, as compared to the relatively colder 1960,1980 period, especially for winter. Indices of temperature extremes defined using fixed limits for maximum and minimum temperatures for colder or warmer days were compared with percentile-based indices defined in the recent literature. The comparison shows that the frequency of warmer days increased during both summer and winter, especially during the last two decades. The observed positive tendencies in minimum temperatures and warmer days during winter occur even though extreme cold events and freezing conditions occurred in 1975, 1994 and 2000. Copyright © 2007 Royal Meteorological Society [source]

An Exploration of the Relationship Between Depressive Symptoms and Cortisol Rhythms in Colorado Ranchers

THE JOURNAL OF RURAL HEALTH, Issue 1 2009
Emily Schulze MA
ABSTRACT:,Context: Although the effects of stress on health have been studied in numerous urban-dwelling populations, fewer studies have addressed these effects in rural populations, such as farmers and ranchers. Purpose: The present study focuses on seasonal levels of depressed affect and perceived stress in Western Colorado ranchers, and how those phenomena related to their levels of cortisol. Methods: Twenty-one (21) ranchers, who were permittees on the Colorado Grand Mesa, completed the study. Participants identified 2-week time periods during the year representing relative high, medium, and low stress. During each period, participants took saliva samples, rated stress levels, and completed a daily health diary. In addition, the Beck Depression Inventory (BDI-II), the perceived stress scale (PSS), and a life events scale (LES) were administered. Results: Results showed a strong relationship between BDI-II and PSS scores (r = 0.748, P < .01). The decreased daytime cortisol decline supports the notion that the hypothalamic-pituitary-adrenal (HPA) axis negative feedback loop is disrupted in chronic stress and depression, thus resulting in chronically elevated cortisol levels. Conclusion: This study supports the relationship between stress, depression, and HPA dysregulation in ranchers. [source]