Cost of reproduction in a long-lived bird: incubation effort reduces immune function and future reproduction

Life-history theory predicts that increased current reproductive effort should lead to a fitness cost. This cost of reproduction may be observed as reduced survival or future reproduction, and may be caused by temporal suppression of immune function in stressed or hard-working individuals. In birds, consideration of the costs of incubating eggs has largely been neglected in favour of the costs of brood rearing. We manipulated incubation demand in two breeding seasons (2000 and 2001) in female common eiders (Somateria mollissima) by creating clutches of three and six eggs (natural range 3-6 eggs). The common eider is a long-lived sea-duck where females do not eat during the incubation period. Mass loss increased and immune function (lymphocyte levels and specific antibody response to the non-pathogenic antigens diphtheria and tetanus toxoid) was reduced in females incubating large clutches. The increased incubation effort among females assigned to large incubation demand did not lead to adverse effects on current reproduction or return rate in the next breeding season. However, large incubation demand resulted in long-term fitness costs through reduced fecundity the year after manipulation. Our data show that in eiders, a long-lived species, the cost of high incubation demand is paid in the currency of reduced future fecundity, possibly mediated by reduced immune function.     

Spatial scaling of population synchrony in marine fish depends on their life history

The synchrony of population dynamics in space has important implications for ecological processes, for example affecting the spread of diseases, spatial distributions and risk of extinction. Here, we studied the relationship between spatial scaling in population dynamics and species position along the slow‐fast continuum of life history variation. Specifically, we explored how generation time, growth rate and mortality rate predicted the spatial scaling of abundance and yearly changes in abundance of eight marine fish species. Our results show that population dynamics of species' with ‘slow’ life histories are synchronised over greater distances than those of species with ‘fast’ life histories. These findings provide evidence for a relationship between the position of the species along the life history continuum and population dynamics in space, showing that the spatial distribution of abundance may be related to life history characteristics.     

Hemodynamic Changes During Long Meditation

Changes in heart rate (HR) and blood pressure (BP) in advanced male meditators during 1 hr of meditation were compared with matched control participants resting for 1 hr. Also, changes in HR and BP during 3-hr meditation were analyzed. HR was recorded continuously during meditation (n = 38) and the control rest (n = 21). BP was measured before and after the meditation (n = 44) and the rest (n = 30). During the first hour, HR declined more in the meditators than the controls (p < .01). Within participant variability of HR was significantly lower during meditation than rest (p < .05). In the second hour of meditation, HR declined further (p = .01). BP was unaffected by either meditation or rest. In conclusion, meditation reduced the level of HR and within participant variability of HR more than rest. HR continued to decline during the second hour of meditation.     

Effects of Diverse Environmental Conditions on φLC3 Prophage Stability in Lactococcus lactis

The effects of various growth conditions on spontaneous LC3 prophage induction in Lactococcus lactis subsp. cremoris IMN-C1814 was analyzed with a half fraction of a 4⁴ factorial experimental design. The four factors included in the study were nutrient availability, acidity, osmolarity, and temperature, each applied at four levels. These environmental factors are related to the fermentation processes in the dairy industry, in which bacteriophage attacks on sensitive starter strains are a constant threat to successful fermentation processes. The frequency of spontaneous LC3 induction was determined by quantitative analyses of restored DNA attachment sites (attB) on the bacterial chromosomes in a population of lysogenic cells. Statistical analysis revealed that all four environmental factors tested affected LC3 prophage stability and that the environmental factors were involved in interactions (interactions exist when the effect of one factor depends on the level of another factor). The spontaneous LC3 induction frequency varied from 0.08 to 1.76%. In general, the induction frequency remained at the same rate or decreased when level 1 to 3 of the four environmental factors was applied. At level 4, which generally gave the least favorable growth conditions, the induction frequency was either unchanged, decreased, or increased, depending on the type of stress. It appeared that the spontaneous induction frequency was independent of the growth behavior of the host. It was the environmental growth conditions that were the decisive factor in induction frequency.     

Continuous and discrete extreme climatic events affecting the dynamics of a high-arctic reindeer population

Climate at northern latitudes are currently changing both with regard to the mean and the temporal variability at any given site, increasing the frequency of extreme events such as cold and warm spells. Here we use a conceptually new modelling approach with two different dynamic terms of the climatic effects on a Svalbard reindeer population (the Brøggerhalvøya population) which underwent an extreme icing event (“locked pastures”) with 80% reduction in population size during one winter (1993/94). One term captures the continuous and linear effect depending upon the Arctic Oscillation and another the discrete (rare) “event” process. The introduction of an “event” parameter describing the discrete extreme winter resulted in a more parsimonious model. Such an approach may be useful in strongly age-structured ungulate populations, with young and very old individuals being particularly prone to mortality factors during adverse conditions (resulting in a population structure that differs before and after extreme climatic events). A simulation study demonstrates that our approach is able to properly detect the ecological effects of such extreme climate events.     

Attachment of A-431 cells on immobilized antibodies to the EGF receptor promotes cell spreading and reorganization of the microfilament system

EGF-like sequences, inherent in a number of extracellular matrix proteins, participate in cell adhesion. It is possible that interactions of these sequences with EGF receptors (EGFR) affect actin filament organization. It was shown previously [Khrebtukova et al., 1991: Exp. Cell Res. 194:48-55] that antibodies specific to EGFR induce capping of these receptors and redistribution of cytoskeletal proteins in A-431 cells. Here we report that A-431 cells attach and spread on solid substrata coated with antibodies to EGFR, even in the absence of serum. Thus, EGFR can act as an adhesion protein and promote microfilament reorganization. Binding of the cells to the EGFR-antibody resulted in the formation of a unique cell shape characterized by numerous, actin-based filopodia radiating from the cell body, but without membrane ruffles. There was also a conspicuous circular belt of actin-containing fibers inside the cell margin, and many irregular actin aggregates in the perinuclear area. The morphologies and actin distributions in A-431 cells spread on fibronectin or laminin 2/4 were very different. On fibronectin, cells had polygonal shapes with numerous stress-fibers and thick actin-containing fibers along the cell edges. On laminin-covered substrata, the cells became fusiform and acquired broad leading lamellae with ruffles. In these cells, there were also a few bundles of filaments running the whole length of the cell body, and shorter bundles extending through the leading lamellae towards the membrane ruffles in the cell edge. These effects and those seen with immobilized EGF suggest that different ligand/receptor complexes induce specific reorganizations of the microfilament system.     

Growth of pellets of a basidial fungus pleurotus ostreatus under various cultivation conditions

Studies on the pelletization of fungus Pleurotus ostreatus have established the pellets to differ as to the size, density and chemical composition. Changes in the pellets, taking place during culture growth, are helpful in studying the mode of their development. We have studied various conditions of cultivation, and established the factors enhancing culture growth. Prehomogenization of seeds, velocity of stirrer revolution, partial pressure of dissolved oxygen and that of other factors was established to affect the structure of pellets and parameters of culture growth.     

Local variation in arctic fox abundance on Svalbard,Norway

Arctic fox (Alopex lagopus) numbers vary greatly, with cyclic fluctuations often associated with fluctuations in microtine rodents. However, in areas where small prey mammals are absent, such as Iceland and Svalbard, such cyclic fluctuations are lacking. Annual fluctuations in the density of the arctic fox population on the Brøggerhalvøya peninsula and Kongsfjorden region on Svalbard, Norway, were studied from 1990 to 2001 by using indices of fox abundance. All indices showed similar trends; fox numbers were low in 1990, increased until 1995 whereupon they decreased sharply, before increasing again and levelling off in 2001. Increasing numbers of foxes during the first part of the study paralleled increasing numbers of Svalbard reindeer (Rangifer tarandus platyrhynchus) carcasses in winter and increasing numbers of nesting barnacle geese (Branta leucopsis) in summer. This study shows that the number of arctic foxes varies greatly even in areas without fluctuating microtine rodents.     

Lysophosphatidic Acid Receptor Type 1 (LPA1) Plays a Functional Role in Osteoclast Differentiation and Bone Resorption Activity

Lysophosphatidic acid (LPA) is a natural bioactive lipid that acts through six different G protein-coupled receptors (LPA_1–6) with pleiotropic activities on multiple cell types. We have previously demonstrated that LPA is necessary for successful in vitro osteoclastogenesis of bone marrow cells. Bone cells controlling bone remodeling (i.e. osteoblasts, osteoclasts, and osteocytes) express LPA₁, but delineating the role of this receptor in bone remodeling is still pending. Despite Lpar1^−/− mice displaying a low bone mass phenotype, we demonstrated that bone marrow cell-induced osteoclastogenesis was reduced in Lpar1^−/− mice but not in Lpar2^−/− and Lpar3^−/− animals. Expression of LPA₁ was up-regulated during osteoclastogenesis, and LPA₁ antagonists (Ki16425, Debio0719, and VPC12249) inhibited osteoclast differentiation. Blocking LPA₁ activity with Ki16425 inhibited expression of nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) and dendritic cell-specific transmembrane protein and interfered with the fusion but not the proliferation of osteoclast precursors. Similar to wild type osteoclasts treated with Ki16425, mature Lpar1^−/− osteoclasts had reduced podosome belt and sealing zone resulting in reduced mineralized matrix resorption. Additionally, LPA₁ expression markedly increased in the bone of ovariectomized mice, which was blocked by bisphosphonate treatment. Conversely, systemic treatment with Debio0719 prevented ovariectomy-induced cancellous bone loss. Moreover, intravital multiphoton microscopy revealed that Debio0719 reduced the retention of CX₃CR1-EGFP⁺ osteoclast precursors in bone by increasing their mobility in the bone marrow cavity. Overall, our results demonstrate that LPA₁ is essential for in vitro and in vivo osteoclast activities. Therefore, LPA₁ emerges as a new target for the treatment of diseases associated with excess bone loss.