Reproductive collapse in European beech results from declining pollination efficiency in large trees

Climate warming increases tree mortality which will require sufficient reproduction to ensure population viability. However, the response of tree reproduction to climate change remains poorly understood. Warming can reduce synchrony and interannual variability of seed production (“masting breakdown”) which can increase seed predation and decrease pollination efficiency in trees. Here, using 40 years of observations of individual seed production in European beech (Fagus sylvatica), we showed that masting breakdown results in declining viable seed production over time, in contrast to the positive trend apparent in raw seed count data. Furthermore, tree size modulates the consequences of masting breakdown on viable seed production. While seed predation increased over time mainly in small trees, pollination efficiency disproportionately decreased in larger individuals. Consequently, fecundity declined over time across all size classes, but the overall effect was greatest in large trees. Our study showed that a fundamental biological relationship—correlation between tree size and viable seed production—has been reversed as the climate has warmed. That reversal has diverse consequences for forest dynamics; including for stand- and biogeographical-level dynamics of forest regeneration. The tree size effects suggest management options to increase forest resilience under changing climates.     

Temporal Association Between Pulmonary Inflammation and Antioxidant Induction Following Hyperoxic Exposure of the Preterm Guinea Pig

The time course and nature of the pulmonary inflammatory and antioxidant responses, both during and after hyperoxic-induced acute lung injury were studied in the preterm guinea pig. Three-day preterm (65 days gestation) guinea pigs were randomly exposed to either 21% O₂ (control) or 95% O₂ (hyperoxia) for 72 hours. All pups were then maintained in ambient conditions for up to a further 11 days, during which time lung damage was monitored. In animals exposed to hyperoxia, evidence of acute lung injury and inflammation was characterized by a marked increase in microvascular permeability and elevated numbers of neutrophils in bronchoalveolar lavage fluid. Protein concentration, elastase-like activity and elastase-inhibitory capacity in lavage fluid were at a maximum at the end of the 72 hours hyperoxic exposure. Four days later, all values had returned to control levels. In contrast, increased numbers of neutrophils, macrophages and lymphocytes were recovered in the lavage fluid during this early recovery period. Coinciding with the influx of inflammatory cells, there was a significant increase in glutathione peroxidase, manganese superoxide dismutase and catalase activities in immature lung. Lung copper/zinc superoxide dismutase activity remained unchanged during both experimental periods. The strong temporal relationship between the influx of inflammatory cells to the lung and the induction of pulmonary antioxidant enzyme defences suggests that a common mechanism underlies both responses. These findings have led us to regard inflammation in the hyperoxic-injured immature lung as a beneficial event and not, as previously suggested, as part of the injurious process.     

Prediction of osteoporotic fractures by postural instability and bone density.

OBJECTIVE--To investigate the utility of risk factors such as bone mineral density, lifestyle, and postural stability in the prediction of osteoporotic fractures. DESIGN--Longitudinal, epidemiological, and population based survey. SETTING--City of Dubbo, New South Wales. SUBJECTS--All residents of Dubbo aged > or = 60 on 1 January 1989. MAIN OUTCOME MEASURE--Incidence of fracture for individual subjects. RESULTS--The overall incidence of atraumatic fractures in men and women was 1.9% and 3.1% per annum respectively. The predominant sites of fracture were hip (18.9%), distal radius (18.5%), ribs and humerus (11.9% in each case), and ankle and foot (9.1% and 6.6% respectively). Major predictors of fractures in men and women were femoral neck bone mineral density, body sway, and quadriceps strength. Age, years since menopause, height, weight, and lifestyle factors were also correlated with bone mineral density and body sway and hence were indirect risk factors for fracture. Discriminant function analysis correctly identified 96% and 93% (sensitivities 88% and 81%) of men and women, respectively, who subsequently developed atraumatic fractures. Predictions based on this model indicated that a woman with a bone mineral density in the lowest quartile in the hip together with high body sway had a 8.4% probability of fracture per annum. This represented an almost 14-fold increase in risk of fracture compared with a woman in the highest bone mineral density quartile with low postural sway. An individual with all three predictors in the "highest risk" quartile had a 13.1% risk of fracture per annum. CONCLUSIONS--Bone mineral density, body sway, and muscle strength are independent and powerful synergistic predictors of fracture incidence.     

RESTRICTED MIGRATION AND THE EVOLUTION OF ALTRUISM

A suggestion that limited migration, i.e., population viscosity, should favor the evolution of altruism has been challenged by recent kin selection models explicitly incorporating restricted migration. It is demonstrated that these models compound two distinct elements of population structure, spatial-genotypic variation and density regulation. These two characteristics are often determined by distinct biological processes. While they may be linked under certain circumstances, this is not invariably true. A simple modification of the migration system employed in these studies decouples migration and population regulation thus favoring inter-group selection. At least in some cases, restricted migration will facilitate the evolution of altruism.