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41.
Gradients in stream fish assemblages across a Mediterranean landscape: contributions of environmental factors and spatial structure 总被引:10,自引:0,他引:10
M. FILOMENA MAGALHÃES DIOGO C. BATALHA & MARIA JOÃO COLLARES-PEREIRA 《Freshwater Biology》2002,47(5):1015-1031
1. Despite wide recognition that fish assemblages are influenced by factors operating over a range of spatial scales, little effort has been devoted to quantifying large‐scale variation and the multiscale dependencies of assemblage patterns and processes. This is particularly true for Mediterranean streams, where seasonally predictable drying‐up may lead to a strong association between assemblage attributes and large‐scale factors affecting the distribution of population sources and extinction likelihood. 2. The contribution of large‐scale factors to stream fish assemblage variation was quantified across a Mediterranean landscape, in south‐west Portugal. Fish abundance and species composition were estimated at 166 sites across third‐ to sixth‐order streams, in March–July 1998. Variance partitioning by redundancy analyses was used to analyse assemblage variation against three sets of predictor variables: environmental (catchment position, and geomorphic and hydrological factors), large‐scale spatial trends and neighbourhood effects. 3. Environmental variables and spatial trends accounted for 34.6% of the assemblage variation across the entire region, and for 36.6 and 57.8% within the two largest catchments (Mira and Seixe). Neighbourhood effects were analysed at the catchment scale, increasing the explained variation to 56.1% (Mira) and 70.7% (Seixe). 4. A prevailing environmental gradient was reflected in an increase in the abundance of all species and size‐classes in relation to catchment position, with more fish present in larger streams and in downstream reaches. Variables describing geomorphic and hydrological settings were less important in explaining assemblage variation. 5. Spatial trends always accounted for the smallest fraction of assemblage variation, and they were probably associated with historical barriers to fish dispersal. The strong neighbourhood effects may be related to spatially autocorrelated habitat conditions, but they are also a likely consequence of fish emigration/extinction and colonisation processes. 6. These results emphasise that a substantial proportion of fish assemblage variation in Mediterranean streams may be explained by large‐scale factors, irrespective of microhabitats and local biotic interactions. It is suggested that this pattern results to a large extent from the seasonal drying‐up, with the summer shortage of surface water limiting fish occurrence in headwaters, and consequently the key core areas for fish concentrating in larger streams and tributaries adjacent to large streams because of neighbourhood effects. 相似文献
42.
Knowledge on interspecific pre‐ and post‐zygotic isolation mechanisms provides insights into speciation patterns. Using crosses (F1 and backcrosses) of two closely related flea beetles species, Altica fragariae and A. viridicyanea, specialized on different hosts in sympatry, we measured: (a) the type of reproductive isolation and (b) the inheritance mode of preference and host‐specific performance, using a joint‐scaling test. Each species preferred almost exclusively its host plant, creating strong prezygotic isolation between them, and suggesting that speciation may occur at least partly in sympatry. Reproductive isolation was intrinsic between females of A. fragariae and either A. viridicyanea or F1 males, whereas the other crosses showed ecologically dependent reproductive isolation, suggesting ecological speciation. The genetic basis of preference and performance was at least partially independent, and several loci coded for preference, which limits the possibility of sympatric speciation. Hence, both ecological and intrinsic factors may contribute to speciation between these species. 相似文献
43.
44.
Pravenec M Kren V Krenová D Zídek V Simáková M Musilová A Vorlícek J Lezin ES Kurtz TW 《Physiological research / Academia Scientiarum Bohemoslovaca》2003,52(3):285-289
Total genome scans of genetically segregating populations derived from spontaneously hypertensive rats (SHR) and other rat models of essential hypertension suggested a presence of quantitative trait loci (QTL) regulating blood pressure on multiple chromosomes, including chromosome 5. The objective of the current study was to test directly a hypothesis that chromosome 5 of the SHR carries a blood pressure regulatory QTL. A new congenic strain was derived by replacing a segment of chromosome 5 in the SHR/Ola between the D5Wox20 and D5Rat63 markers with the corresponding chromosome segment from the normotensive Brown Norway (BN/Crl) rat. Arterial pressures were directly monitored in conscious, unrestrained rats by radiotelemetry. The transfer of a segment of chromosome 5 from the BN strain onto the SHR genetic background was associated with a significant decrease of systolic blood pressure, that was accompanied by amelioration of renal hypertrophy. The heart rates were not significantly different in the SHR compared to SHR chromosome 5 congenic strain. The findings of the current study demonstrate that gene(s) with major effects on blood pressure and renal mass exist in the differential segment of chromosome 5 trapped within the new SHR.BN congenic strain. 相似文献
45.
The byssus production of the blue mussel Mytilus edulis L. was studied in the laboratory in the presence of the metabolites of the following animals: a predator (a starfish Asterias rubens L.) and several species competing with the mussel in White Sea fouling communities (a bivalve Hiatella arctica L. and a solitary ascidian Styela rustica L.). The byssus threads and attachment plaques produced by each mussel per day were counted. The number of byssus threads and plaques was smallest in pure sea water and in the presence of metabolites produced by conspecific individuals. 相似文献
46.
Ola Spjuth Tobias Helmus Egon L Willighagen Stefan Kuhn Martin Eklund Johannes Wagener Peter Murray-Rust Christoph Steinbeck Jarl ES Wikberg 《BMC bioinformatics》2007,8(1):59
Background
There is a need for software applications that provide users with a complete and extensible toolkit for chemo- and bioinformatics accessible from a single workbench. Commercial packages are expensive and closed source, hence they do not allow end users to modify algorithms and add custom functionality. Existing open source projects are more focused on providing a framework for integrating existing, separately installed bioinformatics packages, rather than providing user-friendly interfaces. No open source chemoinformatics workbench has previously been published, and no sucessful attempts have been made to integrate chemo- and bioinformatics into a single framework. 相似文献47.
Zea ribosomal repeat evolution and substitution patterns 总被引:2,自引:1,他引:1
Zea and Tripsacum nuclear ribosomal internal transcribed spacer (ITS)
sequences were used to evaluate patterns of concerted evolution, rates of
substitutions, patterns of methylation-induced deamination, and structural
constraints of the ITS. ITS pseudogenes were identified by their
phylogenetic position, differences in nucleotide composition, extensive
deamination at ancestral methylation sites, and substitutions resulting in
low-stability secondary RNA structures. Selection was important in shaping
the kinds of polymorphisms and substitutions observed in the ITS. ITS
substitution rates were significantly different among the Zea taxa.
Deamination of cytosines at methylation sites was a potent mutation source,
but selection appeared to maintain high methylation site density throughout
the ribosomal repeat except for the gene promoter. Nucleotide divergence
statistics identified selectively constrained regions at the 5' ends of the
ITS1 and ITS2.
相似文献
48.
Agnès Lezin Jenny Martial Géraldine Cancel Giovanni Stevanin Alexander Dürr Yves Agid Alexis Brice Didier Smadja Jean-Claude Vernant Georges-Gabriel Buisson Rémy Bellance Hervé Chneiweiss 《Human genetics》1996,97(5):671-676
Autosomal dominant cerebellar ataxias (ADCAs) are a group of neurodegenerative disorders that are clinically and genetically heterogeneous. We report here a genetic linkage study, with five chromosome 12q markers, of three Martinican families with ADCA type I, for which the spinocerebellar ataxia 1 (SCA1) locus was excluded. Linkage to the SCA2 locus was demonstrated with a maximal lod score of 6.64 at = 0.00 with marker D12S354. Recombinational events observed by haplotype reconstruction demonstrated that the SCA2 locus is located in an approximately 7-cM interval flanked by D 12S 105 and D12S79. Using thez
max-l method, multipoint analysis further reduced the candidate interval for SCA2 to a region of 5 cM. Two families shared a common haplotype at loci spanning 7 cM, which suggests a founder effect, whereas a different haplotype segregated with the disease in the third family. Finally, a mean anticipation of 12 ± 14 years was found in parent-child couples, with no parental sex effect, suggesting that the disease might be caused by an expanded and unstable triplet repeat. 相似文献
49.
50.
Concerted transpositions of mobile genetic elements coupled with fitness changes in Drosophila melanogaster 总被引:3,自引:0,他引:3
Pasyukova EG; Belyaeva ES; Kogan GL; Kaidanov LZ; Gvozdev VA 《Molecular biology and evolution》1986,3(4):299-312
In an inbred low-activity (LA) strain of Drosophila melanogaster with a low
level of fitness and a complex of inadaptive characters, in situ
hybridization reveals an invariant pattern of distribution of three
copia-like elements (mdg-1, mdg-3, and copia). Rare, spontaneous, multiple
transpositions of mobile elements in the LA strain were shown to be coupled
with a drastic increase of fitness. A changed pattern of various types of
mobile elements was also observed on selecting the LA strain for higher
fitness. High-fitness strains show transpositions of mobile elements to
definite chromosomal sites ("hot spots"). Concerted changes in the location
of three different mobile elements were found to be coupled with an
increase of fitness. The mdg-1 distribution patterns were also examined in
two low-fitness strains independently selected from the high-fitness ones.
Fitness decrease was accompanied by mdg-1 excision from the hot spots of
their location usually detected in the high-fitness strains. The results
suggest the existence of a system of adaptive transpositions of mobile
elements that takes part in fitness control.
相似文献