Interannual variation in UV-B and temperature effects on bud phenology and growth in Populus tremula.

Warming affects phenological processes such as spring bud break and autumnal bud set, and also growth rates of trees. Recently, it has been shown that these physiological processes also may be influenced by the ultraviolet-B (UV-B) part of the solar spectrum, and there are reasons to expect that the two environmental factors induce interactive effects when acting in concert. In this study, our aim was to elucidate how experimental enhancements in temperature and UV-B, alone and in combination, affect growth and seasonal phenology of Eurasian aspen (Populus tremula) over several growing seasons (three years). Moreover, we tested how environmentally induced changes in phenology affect the growth achieved over each season, that is, the importance of a prolonged growing season for growth yield. The plants grew in an outdoor experiment with modulated enhancements of temperature and UV-B during the growing season. Both UV-B and temperature enhancement affected bud set dates, while bud break dates were only affected by temperature enhancement. Temperature delayed bud set in all years, but gradually less over years, while UV-B yielded earlier bud set the first year but showed a delayed response the following years. Bud break was always earlier under temperature enhancement. The experimentally induced extension of the growing season in both ends had a positive effect of growth throughout the three-year period. However, the reduced responsiveness of bud set to both enhancement treatments suggest that the plants gradually acclimated to the modified climate, a finding that should also be investigated for other tree species.

The benefits of interpopulation hybridization diminish with increasing divergence of small populations.

Interpopulation hybridization can increase the viability of small populations suffering from inbreeding and genetic drift, but it can also result in outbreeding depression. The outcome of hybridization can depend on various factors, including the level of genetic divergence between the populations, and the number of source populations. Furthermore, the effects of hybridization can change between generations following the hybridization. We studied the effects of population divergence (low vs. high level of divergence) and the number of source populations (two vs. four source populations) on the viability of hybrid populations using experimental Drosophila littoralis populations. Population viability was measured for seven generations after hybridization as proportion of populations facing extinction and as per capita offspring production. Hybrid populations established at the low level of population divergence were more viable than the inbred source populations and had higher offspring production than the large control population. The positive effects of hybridization lasted for the seven generations. In contrast, at the high level of divergence, the viability of the hybrid populations was not significantly different from the inbred source populations, and offspring production in the hybrid populations was lower than in the large control population. The number of source populations did not have a significant effect at either low or high level of population divergence. The study shows that the benefits of interpopulation hybridization may decrease with increasing divergence of the populations, even when the populations share identical environmental conditions. We discuss the possible genetic mechanisms explaining the results and address the implications for conservation of populations.

Predominance of outcrossing in Lymnaea stagnalis despite low apparent fitness costs of self-fertilization.

We have quantified the natural mating system in eight populations of the simultaneously hermaphroditic aquatic snail Lymnaea stagnalis, and studied the ecological and genetic forces that may be directing mating system evolution in this species. We investigated whether the natural mating system can be explained by the availability of mates, by the differential survival of self- and cross-fertilized snails in nature, and by the effects of mating system on parental fecundity and early survival. The natural mating system of L. stagnalis was found to be predominantly cross-fertilizing. Density of snails in the populations had no relationship with the mating system, suggesting that outcrossing rates are not limited by mate availability at the population densities observed. Contrary to expectations for outcrossing species, we detected no evidence for inbreeding depression in survival in nature with inferential population genetic methods. Further, experimental manipulations of mating system in the laboratory revealed that self-fertilization had no effect on parental fecundity, and only minor effects on offspring survival. Predominance of cross-fertilization despite low apparent fitness costs of self-fertilization is at odds with the paradigm that high self-fertilization depression is necessary for maintenance of cross-fertilization in self-compatible hermaphrodites.

Effects of a physical exercise intervention on subjective physical well-being, psychosocial functioning and general well-being among office workers: a cluster randomized-controlled cross-over design.

The purpose of the study was to examine the effects of a workplace physical exercise intervention on subjective physical well-being, psychosocial functioning and general well-being. The study was a cluster randomized-controlled trial with the department (n=4) as the unit of randomization. The subjects (n=90) were office workers [mean age 45.7 (SD 8.5) years]. Psychosocial functioning and well-being variables were measured by descriptive visual rating scales. The cross-over design consisted of one 15-week intervention period of light resistance training and guidance and another 15-week period of no training and no guidance. The statistical analysis was based on linear mixed models. The active component of the intervention, light resistance training, resulted in a slight, but statistically significant, increase in subjective physical well-being (P=0.015). At the average training time of 5 min/working day (25 min/week) the average increase during the 15-week period was 4 units (95% confidence interval (CI) 1-7) and 5% (95% CI 1-9). The physical exercise intervention had no effect on somatic symptoms, anxiety, self-confidence, mood, mental stress at work, working atmosphere, life satisfaction or meaning of life. Daily light resistance training, conducted during the working day, had a positive direction on subjective physical well-being among office workers.