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491.
Frank E. Anderson Adria Pilsits Vladimir Laptikhovsky Eduardo Balguerías Chingis Nigmatulin Uwe Piatkowski Alp Salman 《Journal of experimental marine biology and ecology》2008,364(2):99-109
Alloteuthis is a group of small, slender loliginid squids of minor fisheries importance. There are three nominal Alloteuthis species—A. media (Linnaeus), A. subulata (Lamarck) and A. africana Adam. Two of these species (A. media and A. subulata) have largely overlapping ranges in the Mediterranean and northeastern Atlantic, while A. africana is found along the west coast of Africa. Despite the low level of species diversity, Alloteuthis taxonomy and systematics are confused, and assignment of specimens to species can be difficult. To clarify Alloteuthis systematics, we gathered morphometric data and DNA sequence data from two mitochondrial loci and a nuclear locus from Alloteuthis specimens collected from several localities. Analyses of the morphometric data suggest that head width is the main variable allowing separation of A. africana from the other two species, and central club sucker size separates A. media from A. subulata. One easily diagnosable character often used to distinguish Alloteuthis species—relative fin length—appears to be of little taxonomic value. Only three specimens assignable to A. subulata both morphologically and genetically were found, all from the Adriatic; possible reasons for this apparent rarity are discussed. Gene tree parsimony and coalescent-based methods were used to estimate species relationships from the molecular data, and both supported a sister-species relationship between A. media and A. subulata. Analyses of molecular variation (AMOVA's) revealed significant genetic differentiation between Atlantic and Mediterranean A. media. This study highlights the importance of 1) sampling multiple individuals, locations and loci for species-level phylogenetic studies, 2) using morphometric analyses to reveal taxonomically meaningful morphological characters and 3) accounting for the stochastic nature of the coalescent process when estimating species phylogenies for closely related taxa. 相似文献
492.
493.
Cynthia Akkermans Paul Venema Salman S. Rogers Atze Jan van der Goot Remko M. Boom Erik van der Linden 《Food biophysics》2006,1(3):144-150
We have studied the effect of shear flow on the formation of amyloid fibrils of the whey protein β-lactoglobulin. β-Lactoglobulin aggregates into long, thin, and semiflexible fibrils upon heating at low pH and low ionic strength. Solutions with a protein concentration of 0.5% (w/w) were used, and the formation of fibrils was quantified with flow-induced birefringence, a proportional measure of the length concentration of the fibrils. From the decay of the birefringence after cessation of the flow, a length distribution could be fitted. Pulsed and continuous shear treatment of the samples resulted in a comparable enhancement of the fibrillar growth as compared to the fibrillar growth under quiescent conditions. This indicates that the onset of shear flow is the key parameter for the enhancement of fibrillar growth and not the continuous shear flow itself. This behavior is comparable to a nucleation-like process, during which preaggregates of the fibrils are induced during the onset of the flow and orthokinetic coagulation is absent. However, a difference was present in the length distribution between the pulsed and continuously sheared samples, which can be explained by the homogenizing effect of shear flow. 相似文献
494.
Fusion of mycoplasmas: the formation of cell hybrids 总被引:2,自引:0,他引:2
Borrelia burgdorferi grew more slowly in iron-depleted than in iron-sufficient media. The addition of increasing concentrations of iron stimulated borrelial growth and resulted in the intracellular accumulation of this element. Compared with iron-starved borrelia, iron-enriched organisms showed enhanced sensitivity to hydrogen peroxide. Intracellular iron-content did not, however, influence susceptibility to killing by human polymorphonuclear leucocytes [corrected]. 相似文献