Effects of different base populations on selection response in Drosophila

Oregon‐R, +3, and crossbred strains of Drosophila melanogaster were tested for their response to selection for abdominal bristle number. Various subsidiary tests, consisting of heritability estimations, testing for lethal second and third chromosomes, and chromosome assays were conducted on the selection replicates, which had undergone 14 generations of selection. Evidence showed that a plateau which occurred very early in the +3 high selection replicates was due to fixation of a few additive genes with large effects, thus accounting for the low phenotypic and additive genetic variance, the slight regression in abdominal bristle number on relaxation of selection, the absence of directional dominance, and the low frequency of recessive lethals.

High frequencies of second and third chromosome lethals were found in the Oregon‐R high and low replicates and in the +3 low replicates. That these lethals were not selected for heterozygote superiority for extreme bristle effect was indicated by the slight regression of these replicates on relaxation of selection, and by the absence of high, fluctuating phenotypic variances.

From chromosome assays it appears that the two parental strains had different arrays of genes affecting high bristle number, with these genes located mostly in chromosome II in the Oregon‐R high line but in chromosome III in the +3 high line. In the Crossbred high line, high bristle factors were located in both the second and third chromosomes. The low bristle factors were located mainly in the second chromosome in all three low selection lines.

It appears that the original cross had combined different genes favouring high bristle number, thus allowing greater response in the Crossbred high selection line. The same did not occur for low selection; the response from the Crossbred low line was similar to that of the parental low lines, suggesting that the gene arrays affecting low bristle number in the two original populations were comparable.     

THE EFFECTS OF EXTENDED WORKING HOURS ON HEALTH AND SOCIAL WELL-BEING—A COMPARATIVE ANALYSIS OF FOUR INDEPENDENT SAMPLES

Using structural equation modeling, it can be shown that long weekly working hours and work on weekends, nights, and in shifts have detrimental effects on psychovegetative health. Employees' reported subjective work-life balance also decreases with increasing number of hours worked/week, days worked on weekends, or at nights, and with working shifts. A decrease in work-life balance in turn increases the risk of psychovegetative impairments (PVIs). Thus, long and unusual working hours increase the risk of psychovegetative health impairments both directly and indirectly, moderated by the subjective work-life balance. In fact, the indirect effects of working time on PVIs via the work-life balance seem to be stronger than the direct effects. Results of a cross-validation study of four independent and representative samples from Germany and the European Union (N?>?50,000) indicate high structural stability of these results and thus an increased validity and range for generalization. (Author correspondence: anna.wirtz@gawo-ev.de)     

Metabolic impact assessment for heterologous protein production in Streptomyces lividans based on genome-scale metabolic network modeling

The metabolic impact exerted on a microorganism due to heterologous protein production is still poorly understood in Streptomyces lividans. In this present paper, based on exometabolomic data, a proposed genome-scale metabolic network model is used to assess this metabolic impact in S. lividans. Constraint-based modeling results obtained in this work revealed that the metabolic impact due to heterologous protein production is widely distributed in the genome of S. lividans, causing both slow substrate assimilation and a shift in active pathways. Exchange fluxes that are critical for model performance have been identified for metabolites of mouse tumor necrosis factor, histidine, valine and lysine, as well as biomass. Our results unravel the interaction of heterologous protein production with intracellular metabolism of S. lividans, thus, a possible basis for further studies in relieving the metabolic burden via metabolic or bioprocess engineering.     

Effects of dopaminergic system activation on feeding behavior and growth performance of the sea bass (Dicentrarchus labrax): A self-feeding approach

Dopamine is synthesized from l-dopa and subsequently processed into norepinephrine and epinephrine. Any excess neurotransmitter can be taken up again by the neurons to be broken down enzymatically into DOPAC. The effect of dopamine on mammalian food intake is controversial. Mice unable to synthesize central dopamine die of starvation. However, studies have also shown that central injection of dopamine inhibits food intake. The effect of dopaminergic system in the fish feeding behavior has been scarcely explored. We report that the inclusion of l-dopa in the diets results in the activation of sea bass central dopaminergic system but also in the significant increase of the hypothalamic serotonin levels. Dietary l-dopa induces a decrease of food intake and feed conversion efficiency that drives a decline of all growth parameters tested. No behavioral effects were observed after l-dopa treatment. l-dopa treatment stimulated central expression of NPY and CRF. It suggests that CRF might mediate l-dopa effects on food intake but also that CRF neurons lie downstream of NPY neurons in the hierarchical forebrain system, thus controlling energy balance. Unexpectedly, dietary administration of haloperidol, a D₂-receptor antagonist, cannot block dopamine effects but also induces a decline of the food intake. This decrease seems to be a side effect of haloperidol treatment since fish exhibited a decreased locomotor activity. We conclude that oral l-dopa inhibits sea bass food intake and growth. Mechanism could also involve an increase of hypothalamic serotoninergic tone.     

噬菌体与宿主菌间的角逐

噬菌体和它们的宿主菌组成了地球上教目最庞大的微生物种群,噬菌体靠寄生宿主菌来扩增繁衍。但在漫长的进化中,噬菌体与宿主菌间不单是捕食关系,它们间还形成了复杂的相互对抗机制,其中抵抗防御机制的抗防御机制也会促使抗．抗防御机制的产生。从生态学角度来看,噬菌体和宿主菌间的共进化保持着动态平衡。本文综述近年来这一领域的研究,为更清楚地了解噬菌体与宿主菌间的关系和应用提供了参考。     

The magnitude of local adaptation under genotype‐dependent dispersal

Dispersal moves individuals from patches where their immediate ancestors were successful to sites where their genotypes are untested. As a result, dispersal generally reduces fitness, a phenomenon known as “migration load.” The strength of migration load depends on the pattern of dispersal and can be dramatically lessened or reversed when individuals move preferentially toward patches conferring higher fitness. Evolutionary ecologists have long modeled nonrandom dispersal, focusing primarily on its effects on population density over space, the maintenance of genetic variation, and reproductive isolation. Here, we build upon previous work by calculating how the extent of local adaptation and the migration load are affected when individuals differ in their dispersal rate in a genotype‐dependent manner that alters their match to their environment. Examining a one‐locus, two‐patch model, we show that local adaptation occurs through a combination of natural selection and adaptive dispersal. For a substantial portion of parameter space, adaptive dispersal can be the predominant force generating local adaptation. Furthermore, genetic load may be largely averted with adaptive dispersal whenever individuals move before selective deaths occur. Thus, to understand the mechanisms driving local adaptation, biologists must account for the extent and nature of nonrandom, genotype‐dependent dispersal, and the potential for adaptation via spatial sorting of genotypes.     

Über bakteriostatische Effekte der Darmschleimhaut von Küken mit und ohne Zulage verschiedener Wachstumsstimulatoren zur Nahrung

The supplementation of conjugated linoleic acids (CLA) to the rations of dairy cows represents an opportunity to reduce the content of milk fat. Therefore, CLA have the potential beneficial effect of reducing energy requirements of the early lactating cow. The present study aimed at the examination of long-term and post-treatment effects of dietary CLA intake on performance, variables of energy metabolism-like plasma levels of non esterified fatty acids (NEFA) and ß-hydroxybutyrate (BHB), and fatty acid profile in milk fat. Forty-six pregnant German Holstein cows were assigned to one of three dietary treatments: (1) 100 g/d of control fat supplement (CON), (2) 50 g/d of control fat supplement and 50 g/d of CLA supplement (CLA-1) and (3) 100 g/d of CLA supplement (CLA-2). The lipid-encapsulated CLA supplement consisted of approximately 10% of trans-10, cis-12 CLA and cis-9, trans-11 CLA each. The experiment started 1 d after calving and continued for about 38 weeks, divided into a supplementation (26 weeks) and a depletion period (12 weeks). Over the first 7 weeks of treatment, 11 and 16% reductions in dry matter intake compared to control were observed for the cows fed CLA-1 and CLA-2 supplements respectively. Consequently, the calculated energy balance for these two CLA groups was lower compared to the control. Plasma levels of NEFA and BHB remained unaffected. Later in lactation the highest CLA supplementation resulted in a reduction of milk fat content of 0.7%. However, no reduction in milk fat yield, and accordingly no milk fat depression (MFD), could be shown. The trans-10, cis-12 CLA in milk fat increased with increasing dietary CLA supplementation in a dose-dependent manner. The proportion of C₁₆ in milk fat was decreased by the highest CLA supplementation. With the exception of an increase in plasma glucose level in the CLA-2 group, no post-treatment effects were observed. Overall, under the conditions of the present study no improvement in the calculated energy balance by CLA supplementation could be shown for the entire evaluation period.     

Effect of niacin supplementation on digestibility,nitrogen utilisation and milk and blood variables in lactating dairy cows fed a diet with a negative rumen nitrogen balance

The aim of the present experiment was to determine if a niacin supplementation of 6 g/d to lactating dairy cow diets can compensate negative effects of a rumen nitrogen balance (RNB) deficit. A total of nine ruminally and duodenally fistulated lactating multiparous German Holstein cows were successively assigned to one of three diets consisting of 10 kg maize silage (dry matter [DM] basis) and7 kg DM concentrate: Diet RNB– (n = 6) with energy and utilisable crude protein at the duodenum (uCP) according to the average requirement of the animals but with a negative RNB (–0.41 g N/MJ metabolisable energy [ME]); Diet RNB0 (n = 7) with energy, uCP and a RNB (0.08 g N/MJ ME) according to the average requirement of the animals and, finally, Diet NA (n = 5), which was the same diet as RNB–, but supplemented with 6 g niacin/d. Samples of milk were taken on two consecutive days, blood samples were taken on one day pre- and post-feeding and faeces and urine were collected completely over five consecutive days. The negative RNB reduced milk and blood urea content and apparent total tract digestibility of DM, organic matter (OM) and neutral detergent fibre (NDF). Also N excretion with urine, the total N excreted with urine and faeces and the N balance were reduced when the RNB was negative. Supplementation of niacin elevated plasma glucose concentration after feeding and the N balance increased. Supplementing the diet with a negative RNB with niacin led to a more efficient use of dietary N thereby avoiding the negative effects of the negative RNB on the digestibility of DM, OM and NDF.     

Untersuchungen zur Frage der Methionintoxizität

The study aimed to examine effects of supplemented conjugated linoleic acids (CLA) to periparturient cows receiving different concentrate proportions ante partum (a.p.) to investigate CLA effects on lipid mobilisation and metabolism. Compared to adapted feeding, a high-concentrate diet a.p. should induce a ketogenic metabolic situation post partum (p.p.) to better understand how CLA works. Sixty-four pregnant German Holstein cows had ad libitum access to partial mixed rations 3 weeks prior to calving until day 60 p.p. Ante partum, cows received control fat (CON) or a CLA supplement at 100 g/d, either in a low-concentrate (CON-20, CLA-20) or high-concentrate diet (CON-60, CLA-60). Post partum, concentrate proportion was adjusted, while fat supplementation continued. After day 32 p.p., half of the animals of CLA-groups changed to CON supplementation (CLA-20-CON, CLA-60-CON). A ketogenic metabolic situation p.p. was not achieved and therefore impacts of CLA could not be examined. Live weight, milk yield and composition, blood parameters remained unaffected by the treatments. Only a slightly reduced milk fat yield (not significant) was recorded for Group CLA-20. The proportion of trans-10,cis-12 (t10,c12) CLA in milk fat was significantly increased in CLA-groups compared to CON-groups. With the exception of a reversible CLA effect on milk fat in Group CLA-20, no post-treatment effects occurred. Dry matter intake (DMI) of Group CLA-60 was highest before calving, resulting in a significantly improved estimated energy balance after calving. Ante partum, net energy intakes were significantly increased in high-concentrate groups. Overall, supplemented CLA preparation did not relieve metabolism and lipid mobilisation of early lactating cows. But feeding CLA in a high-concentrate diet a.p. seems to increase DMI and thereby improve the energy balance of cows immediately after calving.     

Effects of malate supplementation on acid-base balance and productive performance in growing/finishing bull calves fed a high-grain diet

This study investigated the effects of malate supplementation on blood acid-base balance and serum lactate levels in a 137-day feedlot experiment with bull calves. Animals were allotted to one of two experimental groups: (1) A control group (no supplementation), and (2) a group receiving a salt of DL-malic acid. Blood pH, pCO₂, HCO₃ ^?, base excess, serum L-lactate and productivity parameters were evaluated. Our data reveal that under the conditions of the present experiment malate supplementation did not have any significant effect on productivity parameters by comparison with non-supplemented animals. As regards acid-base balance, no significant effects attributable only to malate were observed. In conclusion, the time-course and the overall means of serum L-lactate for both groups in both growing and finishing periods (0.44 ± 0.04 mmol/l and 0.39 ± 0.02 mmol/l, respectively, for control animal; and 0.54 ± 0.03 mmol/l and 0.49 ± 0.01 mmol/l, respectively, for supplemented animals) suggests that malate does not have any beneficial effects in animals fed a diet of similar characteristics to that given in this study.