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Evolutionary Status (evolutionary + status)
Selected AbstractsGenetic structure and gene flow in French populations of two Ostrinia taxa: host races or sibling species?MOLECULAR ECOLOGY, Issue 20 2007T. MALAUSA Abstract Most models of ecological speciation concern phytophagous insects in which speciation is thought to be driven by host shifts and subsequent adaptations of populations. Despite the ever-increasing number of studies, the current evolutionary status of most models remains incompletely resolved, as estimates of gene flow between taxa remain extremely rare. We studied the population genetics of two taxa of the Ostrinia genus , one feeding mainly on maize and the other on mugwort and hop , occurring in sympatry throughout France. The actual level of divergence of these taxa was unknown because the genetic structure of populations had been investigated over a limited geographical area and the magnitude of gene flow between populations had not been estimated. We used 11 microsatellite markers to investigate the genetic structure of populations throughout France and the extent of gene flow between the two Ostrinia taxa at several sites at which they are sympatric. We observed clear genetic differentiation between most populations collected on the typical respective hosts of each taxon. However, populations displaying intermediate allelic frequencies were found on hop plants in southern France. Individual assignments revealed that this result could be accounted for by the presence of both taxa on the same host. Gene flow, estimated by determining the proportion of hybrids detected, was low: probably < 1% per generation, regardless of site. This indicates that the two Ostrinia taxa have reached a high level of genetic divergence and should be considered sibling species rather than host races. [source] A photometric,spectroscopic analysis and the evolutionary status of the Algol-type binary U Coronae BorealisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003S. K. Yerli ABSTRACT The prime purposes of this study are to obtain reliable orbital parameters for the Algol-type binary U Coronae Borealis (U CrB) and to explain the evolutionary status of this system. All observations of the primary star's radial velocity are consistent with the value K1= 58.6 ± 2.0 km s,1. Measurements of the radial velocity of the secondary component give K2 = 185.2 ± 5.0 km s,1. Using the photometrically determined inclination of 78.7 ± 0.3, the masses of the two stars are therefore deduced to be 4.74 ± 0.28 and 1.46 ± 0.06 M, for the primary and secondary components, respectively. Using all available observations, we discuss the origin and evolution of the close binary system U CrB. We derive the restrictions concerning masses and period from a general network of calculations of medium mass close binary evolution. Detailed models are calculated within the derived ranges, giving the most likely initial system parameters as and Pi= 1.4 d. It turns out that the interactive evolution up to the present stage has been non-conservative. During its evolution, U CrB has lost about 14 per cent of its initial total mass (,M, 1 M,) and around 18 per cent of its initial total angular momentum. We also examine the possibility of probing dynamo action in the mass-losing component of U CrB. We point out that, in order to maintain the evolution of U CrB in its later stages, which is presumably driven by stellar ,magnetic braking', an efficient mechanism for producing large-scale surface magnetic fields in the donor star is required. We suggest that observed X-ray activity in U CrB may be a good indicator of its evolutionary status and the internal structure of the mass-losing component. [source] Testing of the dwarf galaxy content and the evolutionary status of nearby groups of galaxiesASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009J. Vennik Abstract We carried out visual and parametric searches for dwarf galaxies in five loose groups of galaxies. Follow-up spectroscopy with the HET has shown a 50% success rate of morphological selection. The evolutionary status of the studied groups differs: while the NGC 6962 group has a partially relaxed core, surrounded by an infall region, the NGC 5005/5033 group and the IC 65 group, which consist only of late-type galaxies, are probably still assembling (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Evidence for weak magnetic fields in early-type emission starsASTRONOMISCHE NACHRICHTEN, Issue 10 2007S. Hubrig Abstract We report the results of our study of magnetic fields in a sample of 15 Be stars using spectropolarimetric data obtained at the European Southern Observatory with the multi-mode instrument FORS 1 installed at the 8m Kueyen telescope. We detect weak photospheric magnetic fields in four stars, HD56014, HD148184, HD155806, and HD181615. We note that for HD181615 the evolutionary status is not obvious due to the fact that it is a binary system currently observed in the initial rapid phase of mass exchange between the two components. Further, we notify the possible presence of distinct circular polarisation features in the circumstellar components of Ca II H&K in three stars, HD58011, HD117357, and HD181615, hinting at a probable presence of magnetic fields in the circumstellar mass loss disks of these stars. We emphasize the need for future spectropolarimetric observations of Be stars with detected magnetic fields to study the temporal evolution of their magnetic fields and the correlation of magnetic field properties with dynamical phenomena taking place in the gaseous circumstellar disks of these stars. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||