Biogenic methane contributes to the food web of a large,shallow lake

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Forager age and foraging state,but not cumulative foraging activity,affect biogenic amine receptor gene expression in the honeybee mushroom bodies

Foraging behavior is crucial for the development of a honeybee colony. Biogenic amines are key mediators of learning and the transition from in-hive tasks to foraging. Foragers vary considerably in their behavior, but whether and how this behavioral diversity depends on biogenic amines is not yet well understood. For example, forager age, cumulative foraging activity or foraging state may all be linked to biogenic amine signaling. Furthermore, expression levels may fluctuate depending on daytime. We tested if these intrinsic and extrinsic factors are linked to biogenic amine signaling by quantifying the expression of octopamine, dopamine and tyramine receptor genes in the mushroom bodies, important tissues for learning and memory. We found that older foragers had a significantly higher expression of Amdop1, Amdop2, AmoctαR1, and AmoctβR1 compared to younger foragers, whereas Amtar1 showed the opposite pattern. Surprisingly, our measures of cumulative foraging activity were not related to the expression of the same receptor genes in the mushroom bodies. Furthermore, we trained foragers to collect sucrose solution at a specific time of day and tested if the foraging state of time-trained foragers affected receptor gene expression. Bees engaged in foraging had a higher expression of Amdop1 and AmoctβR3/4 than inactive foragers. Finally, the expression of Amdop1, Amdop3, AmoctαR1, and Amtar1 also varied with daytime. Our results show that receptor gene expression in forager mushroom bodies is complex and depends on both intrinsic and extrinsic factors.     

Cardiac mechanical efficiency is preserved in primary cardiac hypertrophy despite impaired mechanical function

Increased heart size is a major risk factor for heart failure and premature mortality. Although abnormal heart growth subsequent to hypertension often accompanies disturbances in mechano-energetics and cardiac efficiency, it remains uncertain whether hypertrophy is their primary driver. In this study, we aimed to investigate the direct association between cardiac hypertrophy and cardiac mechano-energetics using isolated left-ventricular trabeculae from a rat model of primary cardiac hypertrophy and its control. We evaluated energy expenditure (heat output) and mechanical performance (force length work production) simultaneously at a range of preloads and afterloads in a microcalorimeter, we determined energy expenditure related to cross-bridge cycling and Ca²⁺ cycling (activation heat), and we quantified energy efficiency. Rats with cardiac hypertrophy exhibited increased cardiomyocyte length and width. Their trabeculae showed mechanical impairment, evidenced by lower force production, extent and kinetics of shortening, and work output. Lower force was associated with lower energy expenditure related to Ca²⁺ cycling and to cross-bridge cycling. However, despite these changes, both mechanical and cross-bridge energy efficiency were unchanged. Our results show that cardiac hypertrophy is associated with impaired contractile performance and with preservation of energy efficiency. These findings provide direction for future investigations targeting metabolic and Ca²⁺ disturbances underlying cardiac mechanical and energetic impairment in primary cardiac hypertrophy.     

Genotype accounts for intraspecific variation in the timing and duration of multiple,sequential life-cycle events in a willow species

Premise

Phenological variation among individuals within populations is common and has a variety of ecological and evolutionary consequences, including forming the basis for population-level responses to environmental change. Although the timing of life-cycle events has genetic underpinnings, whether intraspecific variation in the duration of life-cycle events reflects genetic differences among individuals is poorly understood.

Methods

We used a common garden experiment with 10 genotypes of Salix hookeriana (coastal willow) from northern California, United States to investigate the extent to which genetic variation explains intraspecific variation in the timing and duration of multiple, sequential life-cycle events: flowering, leaf budbreak, leaf expansion, fruiting, and fall leaf coloration. We used seven clones of each genotype, for a total of 70 individual trees.

Results

Genotype affected each sequential life-cycle event independently and explained on average 62% of the variation in the timing and duration of vegetative and reproductive life-cycle events. All events were significantly heritable. A single genotype tended to be “early” or “late” across life-cycle events, but for event durations, there was no consistent response within genotypes.

Conclusions

This research demonstrates that genetic variation can be a major component underlying intraspecific variation in the timing and duration of life-cycle events. It is often assumed that the environment affects durations, but we show that genetic factors also play a role. Because the timing and duration of events are independent of one another, our results suggest that the effects of environmental change on one event will not necessarily cascade to subsequent events.     

Disentangling climate change from air pollution effects on epiphytic bryophytes

At the interface between atmosphere and vegetation, epiphytic floras have been largely used as indicators of air quality. The recovery of epiphytes from high levels of SO₂ pollution has resulted in major range changes, whose interpretation has, however, been challenged by concomitant variation in other pollutants as well as climate change. Here, we combine historical and contemporary information on epiphytic bryophyte species distributions, climatic conditions, and pollution loads since the 1980s in southern Belgium to disentangle the relative impact of climate change and air pollution on temporal shifts in species composition. The relationship between the temporal variation of species composition, climatic conditions, SO₂, NO₂, O₃, and fine particle concentrations, was analyzed by variation partitioning. The temporal shift in species composition was such, that it was, on average, more than twice larger than the change in species composition observed today among communities scattered across the study area. The main driver, contributing to 38% of this temporal shift in species composition, was the variation of air quality. Climate change alone did not contribute to the substantial compositional shifts in epiphytic bryophyte communities in the course of the last 40 years. As a consequence of the substantial drop of N and S loads over the last decades, present-day variations of epiphytic floras were, however, better explained by the spatial variation of climatic conditions than by extant pollution loads. The lack of any signature of recolonization delays of formerly polluted areas in the composition of modern floras suggests that epiphytic bryophytes efficiently disperse at the landscape scale. We suggest that a monitoring of epiphyte communities at 10-year intervals would be desirable to assess the impact of raising pollution sources, and especially pesticides, whose impact on bryophytes remains poorly documented.     

Pushed to the edge: Spatial sorting can slow down invasions

Our ability to understand population spread dynamics is complicated by rapid evolution, which renders simple ecological models insufficient. If dispersal ability evolves, more highly dispersive individuals may arrive at the population edge than less dispersive individuals (spatial sorting), accelerating spread. If individuals at the low-density population edge benefit (escape competition), high dispersers have a selective advantage (spatial selection). These two processes are often described as forming a positive feedback loop; they reinforce each other, leading to faster spread. Although spatial sorting is close to universal, this form of spatial selection is not: low densities can be detrimental for organisms with Allee effects. Here, we present two conceptual models to explore the feedback loops that form between spatial sorting and spatial selection. We show that the presence of an Allee effect can reverse the positive feedback loop between spatial sorting and spatial selection, creating a negative feedback loop that slows population spread.     

Effects of formamidoxime on macromolecular synthesis in regenerating liver and hepatomas

Formamidoxime caused an inhibition of [³H]thymidine incorporation into DNA in regenerating liver and transplanted hepatomas of different growth rates when administered by i.p. injection to rats. A dose level of formamidoxime (500 mg/kg body weight) which caused at least a 75% inhibition of DNA synthesis in these tissues had little or no effect on the incorporation of [³H]orotate into total RNA. After administration of formamidoxime there was no significant effect on amino acid nitrogen concentration in the tissues. The incorporation of ³H-labeled amino acids into acid-soluble material, cytoplasmic proteins and acid-insoluble nuclear proteins were either unaffected or showed only small changes after treatment of rats with the drug. In regenerating rat liver and Morris hepatomas 7787 and 7777, formamidoxime caused an inhibition of incorporation of ³H-labeled amino acids into both lysine-rich and arginine-rich histones. In the host livers of rats bearing the transplanted hepatomas, histone synthesis was less affected. The data indicated that formamidoxime causes inhibitory effects which are similar in nature and extent to those previously shown for the structurally related compound, hydroxyurea, in the regenerating rat liver and demonstrated that these effects can also be observed in liver tumors.     

Developmental regulation of 16S acetylcholinesterase and acetylcholine receptors in a mouse muscle cell line

We have studied the appearance, distribution and regulation of acetylcholinesterase (AChE) and acetylcholine receptors (AChRs) in a mouse skeletal muscle cell line (C2), that was originally isolated and described by Yaffe & Saxel [54]. In culture, cells from this line form spontaneously contracting myotubes, with overshooting action potentials that are TTX-sensitive. After fusion of myoblasts into myotubes, there was a dramatic increase in the amount of both AChE and AChR. Three forms of AChE, distinguished by their sedimentation on sucrose gradients, were synthesized: 4-6S, 10S, and 16S. The 4-6S and 10S forms appeared 1 day after the cells began to fuse, whereas the 16S form appeared only 2 days after fusion began. Maximal levels of the 16S AChE form (25-30% of the total) were obtained by reducing the concentration of horse serum in the fusion medium. Prevention of myoblast fusion by reducing the calcium levels in the medium decreased the total AChE by 70%, and only the 4-6S form was synthesized. Blocking spontaneous contractile activity of the myotubes by tetrodotoxin (TTX) led to a 50% reduction in all three esterase forms. Thus, the 16S, or endplate form of AChE is not specifically regulated by electrical or contractile activity in the C2 cell line. After fusion the number of AChRs increased rapidly for 3-4 days and then stabilized. Receptor clusters, ranging from 10-30 micron in length, appeared 1 day after myoblast fusion began. When cells were grown in medium containing reduced Ca2+, the total number of AChRs was decreased by 20-50%. Reduction of Ca2+ after myotubes and AChR clusters had formed resulted in dispersal of AChR clusters. Inhibition of muscle contractions with TTX did not affect the number of AChRs or their distribution.     

African trypanosomiasis: naturally occurring regulatory T cells favor trypanotolerance by limiting pathology associated with sustained type 1 inflammation

Tolerance to African trypanosomes requires the production of IFN-gamma in the early stage of infection that triggers the development of classically activated macrophages controlling parasite growth. However, once the first peak of parasitemia has been controlled, down-regulation of the type 1 immune response has been described. In this study, we have evaluated whether regulatory T cells (Tregs) contribute to the limitation of the immune response occurring during Trypanosoma congolense infection and hereby influence the outcome of the disease in trypanotolerant C57BL/6 host. Our data show that Foxp3+ Tregs originating from the naturally occurring Treg pool expanded in the spleen and the liver of infected mice. These cells produced IL-10 and limited the production of IFN-gamma by CD4+ and CD8+ effector T cells. Tregs also down-regulated classical activation of macrophages resulting in reduced TNF-alpha production. The Treg-mediated suppression of the type 1 inflammatory immune response did not hamper parasite clearance, but was beneficial for the host survival by limiting the tissue damages, including liver injury. Collectively, these data suggest a cardinal role for naturally occurring Tregs in the development of a trypanotolerant phenotype during African trypanosomiasis.