Recruitment patterns of Daphnia: a key for understanding midsummer declines?

The population dynamics of D. galeata was studied during the period May–July of 5 successive years in Bautzen Reservoir (Germany). Sampling intervals of 3–4 days and knowledge of the egg–age distribution made it possible to calculate recruitment of the population for each sampling interval. In every year, high Daphnia densities and high Secchi depth readings (clear-water stage) were recorded in spring. In two of the 5 years, Daphnia abundance remained on a high level throughout summer, whereas in the remaining 3 years a midsummer decline of Daphnia was observed. Birth rates declined while the abundance increased in spring in every year but the timing of this decline in relation to abundance and the onset of the clear-water stage revealed no obvious pattern, distinguishing between years with or without a midsummer decline. However, cumulative recruitment did reveal a clear pattern: in years without a midsummer decline, cumulative recruitment increased slowly, but continually, starting from a low level in early May. By contrast, in years with a midsummer decline, recruitment increased strongly during one week in May, starting from a relatively high density level (>30 ind. l^–1). This quick increase was followed by extended periods with low recruitment. Consequently, in these years the population was dominated by a strong peak-cohort of about the same age during the clear-water stage. If all members of this cohort, while approaching their maximum life-span, die off during a short time interval, this may have a pronounced effect on the initiation of a midsummer decline. From an extensive literature search, evidence is provided that the findings of this study represent a demographic mechanism which is of general importance for the initiation of a midsummer decline in temperate waters.     

Inactivation of the glycine transporter 1 gene discloses vital role of glial glycine uptake in glycinergic inhibition

The glycine transporter subtype 1 (GlyT1) is widely expressed in astroglial cells throughout the mammalian central nervous system and has been implicated in the regulation of N-methyl-D-aspartate (NMDA) receptor activity. Newborn mice deficient in GlyT1 are anatomically normal but show severe motor and respiratory deficits and die during the first postnatal day. In brainstem slices from GlyT1-deficient mice, in vitro respiratory activity is strikingly reduced but normalized by the glycine receptor (GlyR) antagonist strychnine. Conversely, glycine or the GlyT1 inhibitor sarcosine suppress respiratory activity in slices from wild-type mice. Thus, during early postnatal life, GlyT1 is essential for regulating glycine concentrations at inhibitory GlyRs, and GlyT1 deletion generates symptoms found in human glycine encephalopathy.     

Erste Veredlungsversuche mit Apfelunterlagenklonen ausMalus baccata

Zusammenfassung Die ersten 36 im Institut für gärtnerischen Pflanzenbau zu Berlin-Dahlem ausgelesenen Apfelunterlagenklone aus 4 Sämlingsherkünften vonMalus baccata wurden in 2 Veredlungsjahrgängen auf ihre baumschulmäßige Leistung entsprechend früheren Untersuchungen mitMalus-Typen und Klonen aus Apfelwildlingen geprüft. Ihr Ertrag an pflanzwürdigen zweijährigen Hochbüschen wies beträchtliche Unterschiede auf: bei 4 Klonen war er sehr gut, bei I2 gut, bei 7 mittel, bei 4 gering und bei 9 sehr gering. Auch bei den schlechten Gruppen war die Anzahl einjähriger Veredlungen und in diesem Zustande zurückgebliebener zweijähriger Pflanzen häufig recht hoch. Die Augenannahme verbürgte also noch keine normale Weiterentwicklung des Edeltriebes. Auch die Extreme der Wuchsstärken waren außergewöhnlich hoch. Voni9 vergleichbaren Klonen waren 8 äußerst stark, 6 sehr stark, 3 mittelstark und 2 sehr schwach wachsend, während die Gruppen stark und schwach ganz ausfielen. Die im Durchschnitt recht hohe Wuchsleistungszahl wurde im allgemeinen durch einen besonders starken Stamm und längere Seitenäste verursacht. Die größe der einjährigen Veredlungen zeigte keine unbedingte Übereinstimmung mit den Büschen. Wuchsstärke und Ertrag der einzelnen Klone liefen weniger parallel als bei den Wildlingsauslesen, ebenso ergaben sich in dieser Beziehung auch Unterschiede der Sämlingsherkünfte. Bei den veredelten Sorten traten einigermaßen gleich gerichtete Differenzen in Zahl und Größe der Büsche auf.Mit 5 Textabbildungen.Abgeschlossen Januar 1945.     

Dual oscillator model of the respiratory neuronal network generating quantal slowing of respiratory rhythm

We developed a dual oscillator model to facilitate the understanding of dynamic interactions between the parafacial respiratory group (pFRG) and the preBötzinger complex (preBötC) neurons in the respiratory rhythm generation. Both neuronal groups were modeled as groups of 81 interconnected pacemaker neurons; the bursting cell model described by Butera and others [model 1 in Butera et al. (J Neurophysiol 81:382–397, 1999a)] were used to model the pacemaker neurons. We assumed (1) both pFRG and preBötC networks are rhythm generators, (2) preBötC receives excitatory inputs from pFRG, and pFRG receives inhibitory inputs from preBötC, and (3) persistent Na⁺ current conductance and synaptic current conductances are randomly distributed within each population. Our model could reproduce 1:1 coupling of bursting rhythms between pFRG and preBötC with the characteristic biphasic firing pattern of pFRG neurons, i.e., firings during pre-inspiratory and post-inspiratory phases. Compatible with experimental results, the model predicted the changes in firing pattern of pFRG neurons from biphasic expiratory to monophasic inspiratory, synchronous with preBötC neurons. Quantal slowing, a phenomena of prolonged respiratory period that jumps non-deterministically to integer multiples of the control period, was observed when the excitability of preBötC network decreased while strengths of synaptic connections between the two groups remained unchanged, suggesting that, in contrast to the earlier suggestions (Mellen et al., Neuron 37:821–826, 2003; Wittmeier et al., Proc Natl Acad Sci USA 105(46):18000–18005, 2008), quantal slowing could occur without suppressed or stochastic excitatory synaptic transmission. With a reduced excitability of preBötC network, the breakdown of synchronous bursting of preBötC neurons was predicted by simulation. We suggest that quantal slowing could result from a breakdown of synchronized bursting within the preBötC.     

Energetic costs, underlying resource allocation patterns, and adaptive value of predator-induced life-history shifts

We studied costs and benefits of life history shifts of water fleas (genus Daphnia ) in response to infochemicals from planktivorous fish. We applied a dynamic energy budget model to investigate the resource allocation patterns underlying the observed life history shifts and their adaptive value under size selective predation in one coherent analysis. Using a published data set of life history shifts in response to fish infochemicals we show that Daphnia invests less energy in somatic growth in the fish treatment. This observation complies with theoretical predictions on optimal resource allocation. However, the observed patterns of phenotypic plasticity cannot be explained by changes in resource allocation patterns alone because our model-based analysis of the empirical data clearly identified additional bioenergetic costs in the fish treatments. Consequently, the response to fish kairomone only becomes adaptive if the intensity of size selective predation surpasses a certain critical level. We believe that this is the first study that puts resource allocation, energetic costs, and adaptive value of predator induced life-history shifts – using empirical data – into one theoretical framework.     

Eicosanoid-mediated increase in glucose and lactate output as well as decrease and redistribution of flow by complement-activated rat serum in perfused rat liver

Rat serum, in which the complement system had been activated by incubation with zymosan, increased the glucose and lactate output, and reduced and redistributed the flow in isolated perfused rat liver clearly more than the control serum. Heat inactivation of the rat serum prior to zymosan incubation abolished this difference. Metabolic and hemodynamic alterations caused by the activated serum were dose dependent. They were almost completely inhibited by the cyclooxygenase inhibitor indomethacin and by the thromboxane antagonist 4-[2-(4-chlorobenzesulfonamide)-ethyl]-benzene-acetic acid (BM 13505), but clearly less efficiently by the 5'-lipoxygenase inhibitor nordihydroguaiaretic acid and the leukotriene antagonist N-(3-[3-(4-acetyl-3-hydroxy-2-propyl-phenoxy)-propoxy]-4-chlorine-6-meth yl- phenyl)-1H-tetrazole-5-carboxamide sodium salt (CGP 35949 B). Control serum and to a much larger extent complement-activated serum, caused an overflow of thromboxane B2 and prostaglandin F2 alpha into the hepatic vein. It is concluded that the activated complement system of rat serum can influence liver metabolism and hemodynamics via release from nonparenchymal liver cells of thromboxane and prostaglandins, the latter of which can in turn act on the parenchymal cells.     

Life history of Daphnia galeata in a hypertrophic reservoir and consequences of non-consumptive mortality for the initiation of a midsummer decline

SUMMARY 1. Field and laboratory investigations were combined in a 2‐year study on the initiation of a midsummer decline of Daphnia galeata Sars in a hypertrophic reservoir. Quantitative field samples were taken twice a week, and, adult and juvenile mortality rates were calculated. Patterns of reproduction and survival of daphnids born during spring and early summer under fluctuating food conditions were determined in life‐table experiments. 2. The abundance of Daphnia increased strongly in early May and declined in June 1998 (midsummer decline). In 1999, Daphnia density increased only slowly in spring and remained constantly high throughout the summer. 3. Food conditions (concentrations of POC_{<30 μm}) for daphnids deteriorated in both years in response to increasing Daphnia densities, resulting in a clear‐water phase of about 4 weeks. When Daphnia abundance declined in 1998, POC_{<30 μm} concentrations increased greatly, whereas in 1999 food conditions improved only slightly and Secchi depth remained high. 4. Survival of daphnids in life‐table experiments decreased greatly after food became rare and was strongly reduced in those animals born during the clear‐water phase compared with those born later. In addition, age at first reproduction was retarded during the clear‐water phase, resulting in very low population growth rates. Survivorship patterns in life‐table experiments suggest a strong impact of non‐consumptive mortality on Daphnia population dynamics. 5. Field data of mortality point to differences in mortality patterns between years, probably resulting from different predation impacts of juvenile fish. In both years, however, adult mortality contributed substantially to overall mortality at the end of the clear‐water phase. As bottom‐up effects on D. galeata were very similar in both years, the significance of non‐consumptive mortality on the initiation of midsummer declines appears to depend largely on recruitment patterns before the clear‐water phase. A high impact can be expected when Daphnia populations are dominated by a peak cohort of nearly identical age during the clear‐water phase.