Socio-ecological correlates of neophobia in corvids

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Energetics of syntrophic ethanol oxidation in defined chemostat cocultures

The ethanol-oxidizing, proton-reducing Pelobacter acetylenicus was grown in chemostat cocultures with either Acetobacterium woodii, Methanobacterium bryantii, or Desulfovibrio desulfuricans. Stable steady state conditions with tightly coupled growth were reached at various dilution rates between 0.02 and 0.14 h^-1. Both ethanol and H₂ steady state concentrations increased with growth rate and were lower in cocultures with the sulfate reducer < methanogen < homoacetogen. Due to the higher affinity for H₂, D. desulfuricans outcompeted M. bryantii, and this one A. woodii when inoculated in cocultures with P. acetylenicus. Cocultures with A. woodii had lower H₂ steady state concentrations when bicarbonate reduction was replaced by the energetically more favourable caffeate reduction. Similarly, cocultures with D. desulfuricans had lower H₂ concentrations with nitrate than with sulfate as electron acceptor. The Gibbs free energy (G) available to the H₂-producing P. acetylenicus was independent of growth rate and the H₂-utilizing partner, whereas the G available to the latter increased with growth rate and the energy yielding potential of the H₂ oxidation reaction. The critical Gibbs free energy (G_c), i.e. the minimum energy required for H₂ production and H₂ oxidation, was-5.5 to-8.0 kJ mol^-1 H₂ for P. acetylenicus,-5.1 to-6.3 kJ mol^-1 H₂ for A. woodii,-7.5 to-9.1 kJ mol^-1 H₂ for M. bryantii, and-10.3 to-12.3 kJ mol^-1 H₂ for D. desulfuricans. Obviously, the potentially available energy was used more efficiently by homoacetogens > methanogens > sulfate reducers.     

Ischemic flow threshold for striatal dopamine release in rats

To determine the level of cerebral blood flow reduction which causes striatal dopamine release, extracellular dopamine and cerebral blood flow was simultaneously determined using in vivo brain dialysis and a hydrogen clearance method, respectively, in the striatum of spontaneously hypertensive rats, before and during experimental cerebral ischemia. The ischemic flow threshold for neurotransmitter dopamine release was found to be 20% of the resting value or 8–10 ml/100g/min of cerebral blood flow, being similar to those for energy and membrane failures.     

Background selection by the peppered moth (Biston betularia Linn.): individual differences

The hypothesis that dimorphically coloured, cryptic moths select appropriate rest sites by comparing their body scales to substrate reflectance was tested using typical and melanic morphs of the peppered moth, Biston betularia (L.). Experiments designed to block the individual's inspection of its inherited colour phenotype do not support Kettlewell's contrast/conflict (self-inspection) hypothesis. Instead, tracking of marked moths over successive days revealed individual differences in rest-site selection which were not related to treatments, experience (imprinting), nor closely to a moth's inherited colour pattern. Differences between family broods indicate that some genetic bias in background selection exists. The production of artificially selected lines with consistent but opposing preferences will allow us to investigate the co-evolution of pattern and behaviour.     

The respiratory system as an exercise limiting factor in normal trained subjects

Recently, we have shown that an untrained respiratory system does limit the endurance of submaximal exercise (64% peak oxygen consumption) in normal sedentary subjects. These subjects were able to increase breathing endurance by almost 300% and cycle endurance by 50% after isolated respiratory training. The aim of the present study was to find out if normal, endurance trained subjects would also benefit from respiratory training. Breathing and cycle endurance as well as maximal oxygen consumption (VO2max) and anaerobic threshold were measured in eight subjects. Subsequently, the subjects trained their respiratory muscles for 4 weeks by breathing 85-160 l.min-1 for 30 min daily. Otherwise they continued their habitual endurance training. After respiratory training, the performance tests made at the beginning of the study were repeated. Respiratory training increased breathing endurance from 6.1 (SD 1.8) min to about 40 min. Cycle endurance at the anaerobic threshold [77 (SD 6) %VO2max] was improved from 22.8 (SD 8.3) min to 31.5 (SD 12.6) min while VO2max and the anaerobic threshold remained essentially the same. Therefore, the endurance of respiratory muscles can be improved remarkably even in trained subjects. Respiratory muscle fatigue induced hyperventilation which limited cycle performance at the anaerobic threshold. After respiratory training, minute ventilation for a given exercise intensity was reduced and cycle performance at the anaerobic threshold was prolonged. These results would indicate the respiratory system to be an exercise limiting factor in normal, endurance trained subjects.     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

狗的无氧阈与骨骼肌某些特征在锻炼、脱锻炼动态变化中的关系

本实验在体力锻炼与脱锻炼过程中观察了五条成年雄性杂种狗的无氧阈(AT)、骨骼肌毛细血管密度(cap/mm~2)、毛细血管数与肌纤维数之比(C:F)、肌纤维组成——慢肌纤维百分比(％ST)以及毛细血管弥散距离(弥散距离)的变化。结果表明:锻炼前AT与cap/mm~2、C:F,％ST及弥散距离均分别有显著相关。锻炼后第五周,AT、cap/mm~2、C:F和％ST分别增加了40.9％、12.2％、22.9％和2.4％,弥散距离降低6.3％,其中只有AT的增加有显著意义,锻炼十周后,AT增加68.2％(P<0.001)、cap/mm~2增加37.8％(P<0.05)、C:F增加78.1％(P<0.001),弥散距离降低17.0％(P<0.01)而％ST无显著变化。停止锻炼后第五周,AT等各指标都有降低的趋势,但无显著意义,停止锻炼后第12周,AT、cap/mm~2,C:F,％ST分别降低了18.9％、10.9％、10.5％、2.9％,弥散距离增加5.1％,其中除AT的降低有显著意义外,其余指标的变化均无显著意义。与锻炼前相比,这些指标的变化。除％ST外,仍有显著变化。在锻炼与脱锻炼的过程中,AT与cap/mm~2、C:F、弥散距离在各期或整个过程中均呈显著相关,但与％ST相关不显著。实验结果提示,骨骼肌的毛细血管供应状况是决定无氧阈的重要因素之一。     

狗在运动中的肌糖原消耗与无氧阈的关系

本实验测定了5条狗的无氧阈值,运动耐受时间、衰竭时的血乳酸浓度及运动中的肌糖原消耗量。结果如下:无氧阈值,1.与运动耐受时间呈正相关(r=0.947,P<0.02);2.与运动中肌糖原消耗量呈负相关(r=-0.959,P<0.01);3.与衰竭时的血乳酸浓度呈负相关(r=-0.942,P<0.02)。实验结果提示,无氧阈值是反映机体耐力的可靠指标。而运动中肌糖原消耗少,血乳酸积累程度轻,可能是无氧阈值之所以能够反映机体耐力的物质基础。     

长期低浓度SO2对大豆生长和产量的影响

随着化石燃料消耗量不断增加,由此产生的主要大气污染物之一SO_2的浓度和影响范围也日趋增大。SO_2对植物,特别是对农作物的影响已受到普遍重视。本研究选择我国北方种植面积大、分布广的大豆为供试作物,在野外开顶式熏气装置中进行低浓度SO_2长期暴露试验,观察SO_2对大豆生长发育及产量的影响,以期为制订农田大气环境质量标准提供有一定参考价值的生态学基准。