Density-dependent natural selection and trade-offs in life history traits

Theories of density-dependent natural selection state that at extreme population densities evolution produces alternative life histories due to trade-offs. The trade-offs are presumed to arise because those genotypes with highest fitness at high population densities will not also have high fitness at low density and vice-versa. These predictions were tested by taking samples from six populations of Drosophila melanogaster kept at low population densities (r-populations) for nearly 200 generations and placing them in crowded cultures (K-populations). After 25 generations in the crowded cultures, the derived K-populations showed growth rate and productivity that at high densities were elevated relative to the controls, but at low density were depressed.     

Penicillin as epileptogenic agent: its effect on an isolated neuron

Penicillin induces partial depolarization and increased excitability of the neuronal membrane of crayfish stretch receptor. Such effects suggest that the epileptic focus created by the topical application of penicillin to the mammalian cerebral cortex may result from the lowering of the threshold for impluse initiation by excitatory synaptic action within the neuron population.     

Essential role of neutrophils but not mammary alveolar macrophages in a murine model of acute Escherichia coli mastitis

Mastitis, the inflammation of the mammary gland, is an important disease affecting dairy animals worldwide. The disease is caused by mammary pathogenic bacteria and Escherichia coli are frequently implicated. Virulence factors of mammary pathogenic E. coli are only partially known and intramammary challenge with LPS elicits neutrophil recruitment in experimental bovine and murine mastitis models. We have previously shown that neutrophil recruitment in LPS-induced murine mastitis is strictly dependent on mammary alveolar macrophages. However, the relative role of alveolar macrophages and blood neutrophils in E. coli mastitis is not well defined. To this end, we selectively depleted mammary alveolar macrophages or blood neutrophils before intramammary challenge with E. coli strain P4 (ECP4). Mice depleted of alveolar macrophages prior to intramammary challenge recruited neutrophils normally and restricted bacterial growth and interstitial invasion. Importantly however, upon depletion of alveolar macrophages, ECP4 invaded the mammary alveolar epithelial cells and formed intracellular bacterial communities. In contrast, neutrophil depletion prior to intramammary infection with ECP4 was associated with unrestricted bacterial growth, tissue damage, severe sepsis and mortality. This study suggests that neutrophils but not alveolar macrophages provide essential antimicrobial defense against mammary pathogenic E. coli. Furthermore, we show here similar invasion after depletion of alveolar macrophages as in our previous studies showing that LPS/TLR4 signaling on alveolar macrophages abrogates ECP4 invasion of the mammary epithelium. Interestingly, similar ECP4 invasion and formation of intracellular communities were also observed following intramammary infection of either iNOS gene-deficient or IL-1 receptor type 1 gene-deficient mice.     

Dynamics of structural traits in two competing C3 grass species: influence of neighbours and nitrogen

This work analysed the regulatory structural mechanisms involved in the competitive interactions between the annual grass Bromus willdenowii Kunth. (BW = prairie grass) and the perennial C₃ grass Dactylis glomerata L. (DG = orchardgrass) during pasture establishment. Four combinations of species (pure BW, pure DG, DG flanked by BW and BW flanked by DG plants), with and without winter nitrogen fertilization, were factorially arranged in a randomized complete block design. Data were recorded at two organization levels: tillers (three tiller age cohorts) and target plants. Annual neighbours caused a decrease in the number of living leaves in tillers of intermediate age of both species. This structural regulatory mechanism led to a decrease in tiller number per plant and, therefore, restricted the development of horizontal space occupation. Annual neighbours did not cause an increase in tiller size, measured as lamina length or pseudostem height, but decreased root biomass. As a consequence, annual neighbours did not lead the hierarchy in light capture, but limited species radical colonization and competitive ability for soil resources. Winter nitrogen fertilization only affected tiller size in older tillers. These findings emphasize the importance of the cultural decisions, as sowing densities and nitrogen fertilization, to optimize pasture floristic composition.     

Cortisol, adrenocorticotropic hormone, serotonin, adrenaline and noradrenaline serum concentrations in relation to disease and stress in the horse

No detailed comparative data are available on the hormonal parameters of horses suffering from a number of diseases. The aim of our study was to measure concentrations of cortisol, adrenocorticotropic hormone (ACTH), serotonin, adrenaline and noradrenaline in horses with various diseases and following surgery, to assess the response of the HPA axis and adrenal medulla. Blood samples were obtained from six groups of horses comprising a total of 119 animals as follows: laminitis, acute abdominal syndrome (AAS), castration surgery, acute diseases, chronic diseases and healthy controls. Serum hormonal concentrations were determined for each group for comparison. Statistically significant differences between all groups and controls were found for cortisol, ACTH (except for castration), serotonin and adrenaline concentrations but only in horses with laminitis and AAS for noradrenaline. No statistically significant differences were found between males and females. The largest changes in the pituitary-adrenal axis activity occurred mainly in acute diseases, laminitis and in the AAS group.     

Determination of flagellar types by PCR-RFLP analysis of enteropathogenic Escherichia coli (EPEC) and Shiga toxin-producing E. coli (STEC) strains isolated from animals in São Paulo, Brazil

This study evaluated the polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP) analysis of fliC for typing flagella antigen (H) of Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) strains isolated from different animals. The molecular typing of the H type was efficient in the determination of 93 (85%) strains. Two nonmotile (H-) E. coli strains showed a PCR-RFLP electrophoretic profile that did not match known H type patterns. The fliC nucleotide sequence of strains B2N and 4a revealed a nucleotide substitution at the restriction site and a nucleotide insertion that generated a stop codon, respectively. The results of this study showed that PCR-RFLP analysis of fliC is faster, less laborious and as efficient for the determination of H type E. coli isolated from animals, compared to serotyping and that it is useful in determining H type in nonmotile strains and strains expressing non-reactive H antigens. Moreover, the fliC sequence of strain B2N suggests that we could have found a new flagellin antigen type.     

Energy utilization,nitrogen balance and microbial protein supply in cattle fed Pennisetum purpureum and condensed tannins

The aim of the experiment was to assess the effect of condensed tannins (CT) on feed intake, dry matter digestibility, nitrogen balance, supply of microbial protein to the small intestine and energy utilization in cattle fed a basal ration of Pennisetum purpureum grass. Five heifers (Bos taurus × Bos indicus) with an average live weight of 295 ± 19 kg were allotted to five treatments consisting of increasing levels of CT (0, 1, 2, 3 and 4% CT/kg DM) in a 5 × 5 Latin square design. Dry matter intake (DMI) was similar (p > 0.05) between treatments containing 0, 1, 2 and 3% of CT/kg DM and it was reduced (p < 0.05) to 4% CT (5.71 kg DM/day) with respect to that observed with 0% CT (6.65 kg DM/day). Nitrogen balance, purine derivatives excretion in urine, microbial protein synthesis and efficiency of synthesis of microbial nitrogen in the rumen were not affected (p ≥ 0.05) by the increase in the levels of condensed tannins in the ration. Energy loss as CH₄ was on average 2.7% of the gross energy consumed daily. Metabolizable energy intake was 49.06 MJ/day in cattle fed low‐quality tropical grass with a DMI of 6.27 kg/day. It is concluded that concentrations of CT between 2 and 3% of DM of ration reduced energy loss as CH₄ by 31.3% and 47.6%, respectively, without affecting intakes of dry and organic matter; however, digestibilities of dry and organic matter are negatively affected.     

Effect of consumption of molasses/urea blocks on the growth of housed bullocks fedAd libitum withPennisetum purpureum

Summary Ten bullocks in individual pens were providedad libitum with cut chopped pasture grass (Pennisetum purpureum). One group of five animals had access to a molasses/urea block (experimental group) and the other group of five did not (control group). Daily dry matter intakes of 5·04 kg/animal (control group) and 4·83 kg/animal (experimental group) were not significantly different. However the experimental group gained weight at a significantly (P<0·05) faster rate (514 g/animal per day) than the control group (346 g/animal per day). Food conversion efficiency was significantly (P<0·01) better in the experimental group (11·6 kg feed per kg weight gained) than in the control group (16·4 kg feed per kg weight gained). Mean daily intake of the molasses urea blocks was 206 g per animal.

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Efecto consumo de bloques de melaza/urea sobre el crecimiento de bueyes alimentadosAd libitum conPennisetum purpureum

Resumen Se alimentaron 10 bueyes estabulados en corrales individualesad libitum con pasto elefante picado. Cinco de ellos recibieron melaza y urea en forma de bloque, actuando los otros como controles. La ingestión de materia seca no fue significativamente diferente en ambos grupos (4·83 kg/animal vs 5·04 kg/animal, respectivamente). Sin embargo el grupo experimental ganó peso a una tasa más rápida (P<0·05), 514 g/animal día, que los controles 346 g/animal día. La eficiencia en la conversión de alimento fue significativamente mejor (P<0·01) en el grupo experimental (11·6 kg de alimento por kg de peso ganado), que en el grupo control (16·4 kg de alimento por kg de peso ganado). La media de ingestión de melaza/urea fue de 206 g por animal.

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Effect de la consommation de blocs a lecher a base de melasse et d'uree sur la croissance de taurillons en stabulation et nourrisAd libitum avecPennisetum purpureum

Résumé Dix taurillons élevés à l'étable en boxes individuels ont re?uad libitum duPennisetum purpureum coupé sur paturage et fragmenté. Seul un lot de 5 animaux (groupe expérimental) avait accès au bloc à lécher à base de mélasse et d'urée, le groupe témoin en étant écarté. Les consommations quotidiennes de matière sèche n'ont pas été significativement différentes à savoir 5,04 kg/tête pour le groupe témoin et 4,83 kg/tête pour le groupe expérimental. Cependant ce dernier

     

Red muscle development of gilthead sea bream Sparus aurata (L.): structural and ultrastructural morphometry

The transverse red and white muscle area, the superficial red muscle fibres area and their percentages of mitochondria (%mit), myofibrils (%myof) and sarcoplasm (%sarc) were determined in the Mediterranean teleost gilthead sea bream, Sparus aurata (L.). Fish aged from hatching to 78 days were studied. The proportional growth of the red and white muscles was higher for the red muscle in the first half of the larval stage (1-35 days). Then the opposite relationship was observed. The hypertrophic growth of the superficial muscle fibres was continuous except in the first week after hatching. The percentage of mitochondria and percentage of myofibrils showed a significant change just after the half of the larval stage. Whereas the %mit of the superficial muscle fibres was higher than %myof from the first week after hatching to 35 days (average 66.64%), then the %mit decreased significantly and at 73-78 days both parameters were close to an average value of 50%. The meaning of these morphological changes is discussed in relation to the functional role of the red muscle of larvae and the onset of the gills respiration.