Experimental assessment of the fecundity of Eucypris virens (Ostracoda, Crustacea) under natural sex ratios

1. The adaptive significance of the observed variations in sex ratios in non‐marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short‐term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple mating events during the reproductive lifetime of the female. It also emphasizes the need for a minimum number of males, although this minimum number evidently may be rather low, as we found a high number of spermatozoa in the seminal receptacles after a single mating event. 3. The sex ratio in the source population was strongly female biased (1 : 3.4; n = 514), whereas in the hatchling assemblages reared in the laboratory, males and females were found in equal proportions (1 : 1.0; n = 1516), irrespective of the prevailing sex ratio. This clear discrepancy is intriguing, and points to the importance of epigenetic factors for the determination of field sex ratios.     

A Mathematical Model of Photorespiration and Photosynthesis

A comprehensive mathematical model of C₃ leaf carbon metabolism,involving the Calvin cycle and the glycolate and glycerate pathwaysof photorespiration, is formulated in terms of a system of non-lineardifferential equations. A steady state, which is found to beeffectively stable, is derived. The model behaves realisticallywhen tested under varying external carbon dioxide and oxygenconcentrations: photosynthesis is inhibited by higher oxygenlevels, while photorespiration is inhibited by higher carbondioxide levels. Calvin cycle, differential equations, glycolate pathway, mathematical model, photorespiration, photosynthesis     

The Contribution of TRPV4-Mediated Calcium Signaling to Calcium Homeostasis in Endothelial Cells

A large variety of cation transport systems are involved in the regulation of calcium homeostasis in endothelial cells. The focus of the present study is to determine the contribution of nonselective cation channels from the TRP (transient receptor potential) family to cellular calcium homeostasis of porcine aortic endothelial cells (PAEC). One member of the TRPV (vanniloid) subfamily, TRPV4, has previously been shown to be involved in cation transport induced by a large variety of stimulations including osmolarity, temperature, mechanical stress, and phosphorylation. Here, we demonstrate the existence of several TRP proteins, including TRPV4, in PAEC using RT-PCR. To test whether this channel is functional, we performed FURA-2 calcium measurements and whole-cell patch-clamp experiments. We observed the induction of large calcium signals following mechanical stress, altered extracellular temperature, and the selective TRPV4 activator 4-α -PDD. These effects were diminished in the presence of the TRPV4 inhibitor miconazole, suggesting the involvement of this channel in mediating endothelial calcium signals. The large amounts of transported calcium and the short signaling ways suggest a potentially important role of this channel in many physiological processes.     

北极的春季:迁徙鸟类抵达的生物学

一旦鸟类抵达北极区,迁徙鸟类必须调整其生理和行为以适应不可预知的雪盖、天气、食物资源和天敌胁迫。换言之,他们必须抵抗环境干扰(压力)以便尽早迁徙到苔原上的巢区并建立领域。然后,一旦外界环境有利时,它们就立即开始繁殖。这些鸟类的繁殖有一部分是利用低雪盖区域的微生境以及雪融较快的苔原斑块(特别是在柳树Salix sp．附近)。在北极地区,地面温度在日照若干小时后急剧上升,同时无脊椎动物开始活动。风速在地面柳枝和生草丛苔原10cm下几乎减弱为零。这些条件结合在一起提供了理想的避难所,对于早春迁徙到此的雀形目鸟类尤其如此。然而,如果环境调节变得更为恶劣,这些鸟类会离开。因为与南方越冬地相比,春季北极区条件具有潜在的严酷性,所以鸟类对于应激时的肾上腺皮质反应有所调整。雄鸟到达北极地区时对于剧烈应激刺激下的肾上腺酮的分泌有所提高,并且伴随着对于负反馈敏感性的下降和肾上腺皮质层细胞对于促肾上腺皮质激素作用反应的变化。同时,肾上腺酮结合蛋白(CBG)的水平也有所提高,以至于肾上腺酮的作用在恶劣的环境条件下得到缓冲。基因组受体水平的调节,尤其是在脑和肝脏中糖皮质类固醇类似受体与肾上腺酮的低亲合性,以及肾上腺酮的非基因组水平的作用,可能是很重要的。换言之,与抵达生物学有关的激素一行为系统是高度可变的[动物学报50(6)：948-960,2004]。