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排序方式: 共有189条查询结果,搜索用时 15 毫秒
1.
STEFAN MAJORAN 《Zoologica scripta》1987,16(4):277-287
A common structural pattern (as observed under the SEM) in the main body of sectioned sclerites of the family Alcyoniidae, and octocorals in general, is the arrangement of acicular crystals in concentric layers. The crystals roughly follow the direction of the spicule axis, however, the sectioned tubercles of large Sinularia spicules have the acicular crystals oriented in the direction of the tubercles (i.e. perpendicular to the spicule axis), contrary to the sectioned tubercles of Sarcophyton and Lobophytum spicules. They reveal some rod-like structures, furcating the acute processes at the top of the tubercles. Sectioned small, club-like Sinularia sclerites show numerous tiny acicular crystals, oriented with their long axes at a fairly constant degree of inclination around a central axis. SEM studies of sectioned Cladiella sclerites show a granulate structure organized in concentric layers, but lacking acicular crystals. The Silurian Atractosella cataractaca show important characters in common with Recent alcyoniid species. 相似文献
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Population differentiation in Crepis tectorum (Asteraceae): patterns of correlation among characters
STEFAN ANDERSSON 《Biological journal of the Linnean Society. Linnean Society of London》1993,49(2):185-194
This study examines the relationship among traits distinguishing populations of C. tectorum and the extent to which existing trait associations reflect underlying (genetic) tradeoffs. Highly consistent trait associations were found in a comparison of 52 populations representing the western part of the geographical range of the species. In addition to a tight integration of traits reflecting plant stature and inflorescence development, there were consistent links between vegetative and reproductive traits; populations characterized by individuals with large leaves and tall stems with terminal branches usually had larger heads, flowers and fruits (achenes) than those whose individuals had small leaves and a short stem branched from the base. There was a weak negative relationship between the extent of leaf dissection and plant stature; short and compact plants had more deeply lobed leaves than tall plants with terminal branches. Few of these associations were present among families representing a single population of C. tectorum , but there was remarkable similarity between the correlations at the between-population level and those obtained in two segregating F2 progenies of crosses between contrasting populations. Hence, provided that the F2 correlations have a strong genetic basis, it appears that the course of population divergence has been constrained by the underlying correlation structure, although some trait associations may also be a result of selection operating in a correlated fashion on functionally related traits, perhaps leading to linkage disequilibrium of parental traits in the first segregating generation of a cross between ecologically differentiated populations. 相似文献
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HONOR C. PRENTICE STEFAN ANDERSSON EVA MÅNSBY 《Botanical journal of the Linnean Society. Linnean Society of London》2011,166(2):127-148
The perennial herbs Silene vulgaris and S. uniflora are closely related, partially sympatric and interfertile, yet morphologically distinct. We used nuclear (allozyme) and plastid (polymerase chain reaction–restriction fragment length polymorphism) DNA markers to investigate whether these species have a shared history of postglacial colonization and hybridization in Europe, as inferred from large‐scale patterns of geographic variation. The majority of plastid haplotypes and allozyme alleles were widespread and patchily distributed within both species and there was no geographic structure in the distributions of shared allozymes or haplotypes. The mosaic variation is consistent with a scenario in which repeated episodes of interspecific hybridization pre‐dated the largely allopatric range expansion of the two species during the postglacial period. Our overall results are not consistent with a scenario of extensive hybridization and introgression during the postglacial range expansion of the species or within their current areas of sympatry, but we found some evidence for local, postglacial evolution and hybridization in the Baltic region. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 127–148. 相似文献
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MARC DE HERT DAN COHEN JULIO BOBES MARCELO CETKOVICH‐BAKMAS STEFAN LEUCHT DAVID M. NDETEI JOHN W. NEWCOMER RICHARD UWAKWE ITSUO ASAI HANS‐JURGEN MÖLLER SHIV GAUTAM JOHAN DETRAUX CHRISTOPH U. CORRELL 《World psychiatry》2011,10(2):138-151
Physical disorders are, compared to the general population, more prevalent
in people with severe mental illness (SMI). Although this excess morbidity
and mortality is largely due to modifiable lifestyle risk factors, the screening
and assessment of physical health aspects remains poor, even in developed
countries. Moreover, specific patient, provider, treatment and system factors
act as barriers to the recognition and to the management of physical diseases
in people with SMI. Psychiatrists can play a pivotal role in the improvement
of the physical health of these patients by expanding their task from clinical
psychiatric care to the monitoring and treatment of crucial physical parameters.
At a system level, actions are not easy to realize, especially for developing
countries. However, at an individual level, even simple and very basic monitoring
and treatment actions, undertaken by the treating clinician, can already improve
the problem of suboptimal medical care in this population. Adhering to monitoring
and treatment guidelines will result in a substantial enhancement of physical
health outcomes. Furthermore, psychiatrists can help educate and motivate
people with SMI to address their suboptimal lifestyle, including smoking,
unhealthy diet and lack of exercise. The adoption of the recommendations presented
in this paper across health care systems throughout the world will contribute
to a significant improvement in the medical and related psychiatric health
outcomes of patients with SMI. 相似文献
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PHILIPPE HELSEN ROBERT A. BROWNE DAVID J. ANDERSON PETER VERDYCK STEFAN VAN DONGEN 《Biological journal of the Linnean Society. Linnean Society of London》2009,96(2):451-461
Due to the pronounced morphological variation and geographical distribution of Galápagos' Opuntia cacti, numerous hypotheses have been advanced regarding their radiation, diversification, and classification. The currently accepted classification is based on morphology and recognizes six species and fourteen varieties, but the plasticity of many of the characteristics renders any morphological taxonomy problematic. Our analysis of previously published morphological data agrees only partially with the current classification. We present the first molecular phylogeny of these plants. Multiple DNA sequences indicate little genetic distinction among the currently identified species, despite restricted gene flow and limited long distance dispersal within the archipelago. No clear relationship exists between morphological and genetic differences. These results suggest that both molecular and morphological data should be used in conservation planning. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 451–461. 相似文献
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Knowledge of statistical power is essential for sampling design and data evaluation when testing for genetic differentiation. Yet, such information is typically missing in studies of conservation and evolutionary genetics, most likely because of complex interactions between the many factors that affect power. powsim is a 32‐bit Windows/DOS simulation‐based computer program that estimates power (and α error) for chi‐square and Fisher's exact tests when evaluating the hypothesis of genetic homogeneity. Optional combinations include the number of samples, sample sizes, number of loci and alleles, allele frequencies, and degree of differentiation (quantified as FST). powsim is available at http://www.zoologi.su.se/~ryman . 相似文献