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141.
G. C. Grigg L. A. Beard T. Moulton M. T. Queirol Melo L. E. Taplin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(6):445-452
The broad-snouted caiman Caiman latirostris, of South America mostly frequents freshwater but occurs also in estuaries. Nothing of substance is known of its osmoregulatory
physiology but, in the light of accumulating evidence that alligatorids lack specialised adaptations for life in hyperosmotic
waters, we anticipated its physiology would be more similar to that of Alligator mississippiensis than the euryhaline Crocodylus porosus, which has both lingual salt glands and a more complex renal:cloacal system. This proved to be the case. Caiman captured
in estuaries of the Ilha do Cardoso in southern Brazil were effective hypo-osmotic osmoregulators in salinities of 0–24 ppt
(seawater = 35 ppt). Plasma osmolarity, sodium and chloride were similar to those in other crocodilians and not influenced
by salinity. Plasma urea was low and did not vary with salinity. We found no evidence of lingual or other salt glands. Urinary
electrolyte concentrations varied considerably with salinity and in ways reminiscent of A. mississippiensis but very different from C. porosus.
Ca. latirostris dehydrated in seawater more rapidly than C. porosus and had substantially higher integumental permeability to water. Caiman did not drink seawater but rehydrated rapidly when
returned to freshwater (FW). We found small caiman (<500 g) only in very low salinities (<3 ppt) and larger caiman closer
to the sea. We postulate that medium to large Ca. latirostris can take advantage of the feeding opportunities presented by the estuarine mangal despite lacking the physiological specialisations
of crocodylids. Two individuals which we re-sighted by chance had travelled at least 600 m in 2–3 days, showing that every
caiman we captured or saw was within easy reach of FW. Most likely their habitation of the estuary and its mangal is achieved
through a combination of low surface area:volume ratio, relatively impermeable skin, and periodic access to FW.
Accepted: 11 May 1998 相似文献
142.
Loss of phylogenetic information in chorion gene families of Bombyx mori gene conversion 总被引:1,自引:0,他引:1
Regier JC; Weigmann BM; Leclerc RF; Friedlander TP 《Molecular biology and evolution》1994,11(1):72-87
The silkmoth chorion has provided a stimulating model for the study of
evolution and developmental regulation of gene families. Previous attempts
at inferring relationships among chorion sequences have been based on
pairwise comparisons of overall similarity, a potentially problematic
approach. To remedy this, we identified the alignable regions of low
sequence variability and then analyzed this restricted database by
parsimony and neighbor-joining methods. At the deepest level, the chorion
sequence tree is split into two branches, called "alpha" and "beta." Within
each branch, early- and late-expressing genes each constitute monophyletic
groups, while the situation with middle-expressing genes remains uncertain.
The HcB gene family appears to be the most basal beta-branch group, but
this conclusion is qualified because the effect of gene conversion on
branching order is unknown. Previous studies by Eickbush and colleagues
have strongly suggested that ErA, HcA, and HcB families undergo gene
conversion within a gene family, whereas the ErB family does not. The
occurrence of conversion correlates with a particular tree structure;
namely, branch lengths are much greater at the base of the family than at
higher internodes and terminal branches. These observations raise the
possibility that chorion gene families are defined by gene conversion
events (reticulate evolution) rather than by descent with modification
(synapomorphy).
相似文献
143.
144.
G. W. Grigg 《Molecular & general genetics : MGG》1970,106(3):228-238
Summary Caffeine (4 and 8 mM) increased the rate of spontaneous DNA breakdown which occurred during normal growth of a culture of E. coli Bs-11, but neither affected breakdown in the EXR strain Bs-2 nor the parental strain B. It slightly impaired the rate of DNA breakdown which follows UV-irradiation of E. coli B, but did not depress the final fraction degraded. On the other hand even 12 mM caffeine had no detectable effect on the (excessive) rate of DNA breakdown of U. V.-irradiated cultures of the EXR strain Bs-2. The effects of X-irradiation on DNA breakdown in E. coli B and a number of its U. V.-sensitive and resistant mutants are described. Caffeine had no detectable effect on the kinetics of X ray-induced DNA breakdown of E. coli B. 相似文献
145.
Biophysical studies of mechanoreceptors 总被引:4,自引:0,他引:4
Mechanoreception can be viewed as a series of sequential mechanical and ionic processes that take place in mechanosensitive end organs and in the terminals of the nerves that innervate them. Stimuli act on a transducer after being transmitted through some material having a combination of elastic and viscoelastic properties. Channels that open under membrane loading have recently been described in muscle cells and are presented as a model for transduction. When open these channels are cation specific. Ions passing through transducer channels depolarize a spike-initiating zone on the cell. These currents may also activate other conductances in the cell, so that the total generator current may have many components. In many mechanoreceptors, action potential initiation results in activation of an electrogenic Na+ pump at the spike-initiation zone, which modifies the threshold for subsequent action potentials. Action potentials initiated in the many branches of a single sensory axon interact at the branching point of the axon. The rules governing this interaction are complex. The above factors, together or separately, are responsible for the dynamic responses and adaptation observed in mechanoreceptors. 相似文献
146.
147.
Water quality and algal populations in the Vaal River Barrage Reservoir have been monitored extensively for many decades, because of its importance as a water source for the most densely populated area in South Africa. Although Aulacoseira granulata (Ehrenberg) Simonsen is frequently found and at it times dominates algal assemblages in the Barrage, Aulacoseira ambigua (F.Meister) Tuji & D.M.Williams has never before been recorded at this locality. During a countrywide proficiency-testing scheme for algae counting, coordinated by Rand Water, spiral-shaped diatom colonies with distinctly curved cells were detected during May 2015. Upon investigation, it was found that the spiral colonies were Aulacoseira ambigua f. japonica, its presence in the fresh waters of South Africa being recorded for the first time. Since their first appearance during May 2015, colonies of Aulacoseira ambigua f. japonica have been constantly present in the surface waters of the Barrage. Their presence at this site can be linked to increasing eutrophication in the Vaal River, because the spiral form is known to prefer eutrophic conditions. Centric diatoms rarely form spiral colonies and there is some confusion in the literature as to the identity of this particular form, therefore in this paper we discuss this taxon, its nomenclature and ecological significance. 相似文献
148.
Matthew J. Grigg Bridget E. Barber Jutta Marfurt Mallika Imwong Timothy William Elspeth Bird Kim A. Piera Ammar Aziz Usa Boonyuen Christopher J. Drakeley Jonathan Cox Nicholas J. White Qin Cheng Tsin W. Yeo Sarah Auburn Nicholas M. Anstey 《PloS one》2016,11(3)
Background
Malaria caused by zoonotic Plasmodium knowlesi is an emerging threat in Eastern Malaysia. Despite demonstrated vector competency, it is unknown whether human-to-human (H-H) transmission is occurring naturally. We sought evidence of drug selection pressure from the antimalarial sulfadoxine-pyrimethamine (SP) as a potential marker of H-H transmission.Methods
The P. knowlesi dihdyrofolate-reductase (pkdhfr) gene was sequenced from 449 P. knowlesi malaria cases from Sabah (Malaysian Borneo) and genotypes evaluated for association with clinical and epidemiological factors. Homology modelling using the pvdhfr template was used to assess the effect of pkdhfr mutations on the pyrimethamine binding pocket.Results
Fourteen non-synonymous mutations were detected, with the most common being at codon T91P (10.2%) and R34L (10.0%), resulting in 21 different genotypes, including the wild-type, 14 single mutants, and six double mutants. One third of the P. knowlesi infections were with pkdhfr mutants; 145 (32%) patients had single mutants and 14 (3%) had double-mutants. In contrast, among the 47 P. falciparum isolates sequenced, three pfdhfr genotypes were found, with the double mutant 108N+59R being fixed and the triple mutants 108N+59R+51I and 108N+59R+164L occurring with frequencies of 4% and 8%, respectively. Two non-random spatio-temporal clusters were identified with pkdhfr genotypes. There was no association between pkdhfr mutations and hyperparasitaemia or malaria severity, both hypothesized to be indicators of H-H transmission. The orthologous loci associated with resistance in P. falciparum were not mutated in pkdhfr. Subsequent homology modelling of pkdhfr revealed gene loci 13, 53, 120, and 173 as being critical for pyrimethamine binding, however, there were no mutations at these sites among the 449 P. knowlesi isolates.Conclusion
Although moderate diversity was observed in pkdhfr in Sabah, there was no evidence this reflected selective antifolate drug pressure in humans. 相似文献149.
150.
A finite element based method has been developed for measuring strains in soft tissue. An array of markers is placed on the tissue surface and treated as nodes of a four node isoparametric element. The displacements of the marker centroids are directly measured using a high sensitivity television camera. Finite element method mathematics are then used to calculate the plane strain tensor at any point inside the element. The method has been implemented using non-rectangular elements that are approximately 2 mm on each side. 相似文献