Adaptive evolution of color vision of the Comoran coelacanth (Latimeria chalumnae).
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The coelacanth, a "living fossil," lives near the coast of the Comoros archipelago in the Indian Ocean. Living at a depth of about 200 m, the Comoran coelacanth receives only a narrow range of light, at about 480 nm. To detect the entire range of "color" at this depth, the coelacanth appears to use only two closely related paralogous RH1 and RH2 visual pigments with the optimum light sensitivities (lambdamax) at 478 nm and 485 nm, respectively. The lambdamax values are shifted about 20 nm toward blue compared with those of the corresponding orthologous pigments. Mutagenesis experiments show that each of these coadapted changes is fully explained by two amino acid replacements. (+info)
Physiological changes and digestive capabilities of newly received feedlot cattle.
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Newly arrived feedlot calves undergo numerous stressors that result in 1) transient endocrine responses, 2) altered products of energy and protein metabolism, 3) changes in appetite and growth rate, 4) possible limited compromise of digestive and rumen function, and 5) a challenged immune system. The most consistent endocrine and metabolic responses to marketing, transport, and feedlot adaptation are seen with cortisol and epinephrine. In contrast to earlier work done with indirect in vitro gas production measurements, recent research has shown that the ruminal microbial population is able to effectively digest available substrate immediately following a calfs weaning, trucking, and 24 h of feed and water deprivation. Additionally, a period of feed and water deprivation up to 72 h coupled with 8 h of trucking does not reduce the concentration or total numbers of either the viable cellulolytic or total bacteria present in the rumen of newly weaned or feedlot-adapted calves. However, ruminal volume, DM, total weight of ruminal contents, and total protozoal numbers decrease as duration of feed deprivation increases. To compensate for the reduced DMI that occurs in the first 2 wk after arrival at the feedlot, increased nutrient density is needed to meet an animal's requirements for nutrients. Limited data suggest that newly arrived calves prefer a diet that is similar in moisture and texture to feeds with which they are familiar. Additionally, modification of the stress-associated behavior using trainer animals may improve the feed intake of newly received calves and may reduce calf morbidity. (+info)
Odor coding in a model olfactory organ: the Drosophila maxillary palp.
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Odor coding relies on the activity of different classes of receptor neurons, each with distinct response characteristics. We have examined odor coding in a model olfactory organ, the maxillary palp of Drosophila. This organ contains only 120 olfactory receptor neurons, compartmentalized in sensory hairs called sensilla, and provides an opportunity to characterize all neurons in an entire olfactory organ. Extensive extracellular recordings from single sensilla reveal that the neurons fall into six functional classes. Each of the 60 sensilla houses two neurons, which observe a pairing rule: each sensillum combines neurons of two particular classes, thereby yielding three sensillum types. The sensillum types are intermingled on the surface of the palp, but their distribution is not random. The neurons exhibit diverse response characteristics, providing the basis for an olfactory code. A particular odor can excite one neuron and inhibit another, and a particular neuron can be excited by one odor and inhibited by another. Some excitatory responses continue beyond the end of odor delivery, but responses to most odors terminate abruptly after the end of odor delivery, with some followed by a period of poststimulus quiescence. The specificity of odor response is examined in detail for the neurons of one sensillum, which were found to differ in their relative responses to a homologous series of esters. Adaptation and cross-adaptation are documented, and cross-adaptation experiments demonstrate that the two neurons within one type of sensillum can function independently. The analysis of all neuronal types in this model olfactory organ is discussed in terms of its functional organization and the mechanisms by which it encodes olfactory information. (+info)
Combined use of several preferred retinal loci in patients with macular disorders when reading single words.
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To investigate the use of several preferred retinal loci (PRL) when attempting to read, two patients with bilateral central scotomas were asked to decipher single words, successively projected onto the retina using a scanning laser ophthalmoscope (SLO). Video-recordings of the fundus image, on which the projected targets were superimposed, were analyzed frame by frame. One patient used two PRL in association and the other used three, each PRL having a specific function. Single word reading made it easier than with full texts to correlate the images parts scrutinized and the retinal areas involved. Then, as patients were unable to describe their reading behavior, the examiner monitored refixation movements using the SLO and asked questions to help them to become aware of their reading behavior. Eventually, they could localize their PRL, describe their specific functions, and switch at will between them. (+info)
Cardiovascular consequences of renal anaemia and erythropoietin therapy.
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Cardiovascular disease is the leading cause of increased mortality in patients with renal failure and vigorous attention to cardiovascular risk factors is therefore required to improve patient outcome. The availability of recombinant human Epo has focused the interest on the role of chronic anaemia in the pathogenesis of cardiovascular disease. Severalfold evidence indicates that anaemia can contribute to cardiac volume overload and together with overhydration, fistula flow and the pressure overload secondary to arterial hypertension, it may play a significant role in the development of cardiac hypertrophy. As in the general population left ventricular hypertrophy is a severe adverse risk factor in renal patients. In addition, in the presence of ischaemic heart disease anaemia may further worsen cardiac oxygen supply. This dual effect of anaemia probably explains why epidemiological studies have shown that a 1 g/dl decrease in haemoglobin levels is an independent, statistically significant risk factor for the development of cardiac morbidity and mortality. Follow-up examinations have demonstrated that partial correction of anaemia with recombinant Epo can improve cardiac oxygen supply and partially reverse pathological changes in left ventricular geometry. However, although partial anaemia correction regularly reduces left ventricular volume, the effects on wall thickness are far less significant. Moreover, in patients with advanced cardiac disease it has recently not been possible to demonstrate that a normalization of haemoglobin levels provides further benefit. It is not unlikely therefore that the development of severe anaemia has to be prevented by early implementation of Epo therapy in order to achieve the maximum benefit with respect to the cardiovascular system. (+info)
The effect of microgravity on morphology and gene expression of osteoblasts in vitro.
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The mass and architecture of the skeletal system adapt, to some extent, to their mechanical environment. A site-specific bone loss of 1-2% is observed in astronauts and in-flight animals after 1 month of spaceflight. Biochemical data of astronauts and histomorphometric analysis of rat bones show that the change in bone mass is a result of decreased bone formation in association with normal (or increased) bone resorption. The changes in bone formation appear to be due in part to decreased osteoblast differentiation, matrix maturation, and mineralization. Recent data show that spaceflight alters the mRNA level for several bone-specific proteins in rat bone, suggesting that the characteristics of osteoblasts are altered during spaceflight. A possible underlying mechanism is that osteoblasts themselves are sensitive to altered gravity levels as suggested by several studies investigating the effect of microgravity on osteoblasts in vitro. Changes in cell and nuclear morphology were observed as well as alterations in the expression of growth factors (interleukin-6 and insulin-like growth factor binding proteins) and matrix proteins (collagen type I and osteocalcin). Taken together, this altered cellular function in combination with differences in local or systemic factors may mediate the effects of spaceflight on bone physiology. (+info)
The role of environmental calcium in freshwater survival of the marine teleost, Lagodon rhomboides.
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(1) The marine teleost fish, Lagodon rhomboides, can only tolerate fresh water (5 mM Na) if Ca is also present (10 mM). Transfer to Ca-free fresh water is followed by a substantial increase in radioactive Na efflux with little or no change in the transepithelial potential. Addition of the chelating agent EDTA (2 mM) further increases Na efflux. Fish left in Ca-free fresh water for 2-5 h die with a total body Na less than 50% of that found in animals acclimated to Ca-supplemented fresh water. (2) Rates of Na uptake were measured on either sea-water-acclimated or Ca-supplemented fresh water-acclimated fish transferred to various low Na media. In both cases Na uptake has a high Km, is saturable, inhibited by external NH4, H and amiloride, and is not related to changes in the trans-epithelial potential. (3) It is suggested that L. rhomboides is dependent upon external Ca to decrease diffusional Na loss in low salinities so that a relatively inefficient Na uptake can balance diffusional and urinary Na loss. (+info)
Mutators, population size, adaptive landscape and the adaptation of asexual populations of bacteria.
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Selection of mutator alleles, increasing the mutation rate up to 10, 000-fold, has been observed during in vitro experimental evolution. This spread is ascribed to the hitchhiking of mutator alleles with favorable mutations, as demonstrated by a theoretical model using selective parameters corresponding to such experiments. Observations of unexpectedly high frequencies of mutators in natural isolates suggest that the same phenomenon could occur in the wild. But it remains questionable whether realistic in natura parameter values could also result in selection of mutators. In particular, the main parameters of adaptation, the size of the adapting population and the height and steepness of the adaptive peak characterizing adaptation, are very variable in nature. By simulation approach, we studied the effect of these parameters on the selection of mutators in asexual populations, assuming additive fitness. We show that the larger the population size, the more likely the fixation of mutator alleles. At a large population size, at least four adaptive mutations are needed for mutator fixation; moreover, under stronger selection stronger mutators are selected. We propose a model based on multiple mutations to illustrate how second-order selection can optimize population fitness when few favorable mutations are required for adaptation. (+info)