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Positive selection is a general phenomenon in the evolution of abalone sperm lysin 总被引:36,自引:21,他引:15
Lysin is a 16kDa acrosomal protein used by abalone sperm to create a hole
in the egg vitelline envelope (VE). The interaction of lysin with the VE is
species-selective and is one step in the multistep fertilization process
that restricts heterospecific (cross-species) fertilization. For this
reason, the evolution of lysin could play a role in establishing prezygotic
reproductive isolation between species. Previously, we sequenced sperm
lysin cDNAs from seven California abalone species and showed that positive
Darwinian selection promotes their divergence. In this paper an additional
13 lysin sequences are presented representing species from Japan, Taiwan,
Australia, New Zealand, South Africa, and Europe. The total of 20 sequences
represents the most extensive analysis of a fertilization protein to date.
The phylogenetic analysis divides the sequences into two major clades, one
composed of species from the northern Pacific (California and Japan) and
the other composed of species from other parts of the world. Analysis of
nucleotide substitution demonstrates that positive selection is a general
process in the evolution of this fertilization protein. Analysis of
nucleotide and codon usage bias shows that neither parameter can account
for the robust data supporting positive selection. The selection pressure
responsible for the positive selection on lysin remains unknown.
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Eric Allan Wolfgang W. Weisser Markus Fischer Ernst-Detlef Schulze Alexandra Weigelt Christiane Roscher Jussi Baade Romain L. Barnard Holger Beßler Nina Buchmann Anne Ebeling Nico Eisenhauer Christof Engels Alexander J. F. Fergus Gerd Gleixner Marlén Gubsch Stefan Halle Alexandra M. Klein Ilona Kertscher Annely Kuu Markus Lange Xavier Le Roux Sebastian T. Meyer Varvara D. Migunova Alexandru Milcu Pascal A. Niklaus Yvonne Oelmann Esther Pašalić Jana S. Petermann Franck Poly Tanja Rottstock Alexander C. W. Sabais Christoph Scherber Michael Scherer-Lorenzen Stefan Scheu Sibylle Steinbeiss Guido Schwichtenberg Vicky Temperton Teja Tscharntke Winfried Voigt Wolfgang Wilcke Christian Wirth Bernhard Schmid 《Oecologia》2013,173(1):223-237
In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination. 相似文献
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Electron microscopy of cyanobacterium Pleurocapsa sp. CALU 1126 revealed that multiple fission proceeds by successive binary fissions. The cultivation conditions were determined when the number of baeocytes (products of multiple fission) was comparable with that of macrocytes (products of binary fission), and cell sorting was achieved for the first time. Juvenile baeocytes were shown to differ from macrocytes in: (1) the absence of sheath; (2) the linear-peripheral configuration of their lamellar system; (3) lower content of phycobiliproteins and higher content of carotenoids; (4) the set of PSII polypeptides. Baeocytes can therefore be considered differentiated cells characterized by the uncoupling between energy and biosynthetic metabolism. 相似文献
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Mitochondrial DNA and bindin gene sequence evolution among allopatric species of the sea urchin genus Arbacia 总被引:3,自引:1,他引:2
Sea urchins of the genus Arbacia (order Stirodonta) have discontinuous
allopatric distributions ranging over thousands of kilometers.
Mitochondrial DNA (mtDNA) sequences were used to reconstruct phylogenetic
relationships of four Arbacia species and their geographic populations.
There is little evidence of genetic structuring of populations within
species, except in two cases at range extremes. The mtDNA sequence
differentiation between species suggests that divergence occurred about 4-9
MYA. Gene sequences encoding the sperm protein bindin and its intron were
obtained and compared with the mtDNA phylogeny. Sea urchins among the
well-studied echinoid order Camarodonta, with degrees of mtDNA divergence
similar to those of Arbacia species, are known to have remarkable variation
in bindin. However, in Arbacia, little variation in deduced amino acid
sequences of bindin was found, indicating that purifying selection acts on
the protein. In contrast, bindin intron sequences showed much
differentiation, including numerous insertion/deletions. Fertilization
experiments performed between a divergent pair of Arbacia species from the
Atlantic and Pacific Oceans revealed no evidence of blocks to gamete
recognition. In Arbacia, fertilization specificities may have evolved
relatively slowly as a result of extensive gene flow within species,
greater functional constraint on the bindin polypeptide, or reduced
selective pressure for species recognition in singly occurring species.
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6.
Females of the sea urchin Strongylocentrotus purpuratus differ in the structures of their egg jelly sulfated fucans 总被引:1,自引:0,他引:1
The egg jelly coats of sea urchins contain sulfated fucans which bind to a
sperm surface receptor glycoprotein to initiate the signal transduction
events resulting in the sperm acrosome reaction. The acrosome reaction is
an ion channel regulated exocytosis which is an obligatory event for sperm
binding to, and fusion with, the egg. Approximately 90% of individual
females of the sea urchin Strongylocentrotus purpuratus spawned eggs having
only one of two possible sulfated fucan electrophoretic isotypes, a slow
migrating (sulfated fucan I), or a fast migrating (sulfated fucan II)
isotype. The remaining 10% of females spawned eggs having both sulfated
fucan isotypes. The two sulfated fucan isotypes were purified from egg
jelly coats and their structures determined by NMR spectroscopy and
methylation analysis. Both sulfated fucans are linear polysaccharides
composed of 1-->3-linked alpha-L-fucopyranosyl units. Sulfated fucan I
is entirely sulfated at the O -2 position but with a heterogeneous
sulfation pattern at O -4 position. Sulfated fucan II is composed of a
regular repeating sequence of 3 residues, as follows: [3-alpha-L-Fuc p -
2,4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-
1]n. Both purified sulfated fucans have approximately equal potency in
inducing the sperm acrosome reaction. The significance of two structurally
different sulfated fucans in the egg jelly coat of this species could
relate to the finding that the sperm receptor protein which binds sulfated
fucan contains two carbohydrate recognition modules of the C-type lectin
variety which differ by 50% in their primary structure.
相似文献
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Christoph Scherber Peter N. Mwangi Martin Schmitz Michael Scherer-Lorenzen Holger Beß ler Christof Engels Nico Eisenhauer Varvara D. Migunova Stefan Scheu Wolfgang W. Weisser Ernst-Detlef Schulze Bernhard Schmid 《Journal of Plant Ecology》2010,3(2):99
Aims Species-rich plant communities are hypothesized to be more resistant against plant invasions because they use resources in a more efficient way. However, the relative contributions of aboveground competition and belowground interactions for invasion resistance are still poorly understood.Methods We compared the performance of Knautia arvensis transplants growing in plots differing in plant diversity both under full competition and with shoots of neighbors tied back to determine the relative strength of aboveground competition in suppressing this test invader without the confounding effect of shading. In addition, we assessed the effects of belowground competition and soil-borne pathogens on transplant performance.Important findings Both aboveground competition and plant species richness strongly and independently affected invader performance. Aboveground biomass, height, leaf mass per area and flowering of transplanted individuals of K. arvensis decreased with increasing species richness of the host community. Species-rich and species-poor communities both imposed equally strong aboveground competition on K. arvensis. However, belowground interactions (especially belowground root competition) had strong negative effects on transplant performance. In addition, the presence of grasses in a plant community further reduced the performance of K. arvensis. Our results suggest that belowground competition can render species-rich host communities more suppressive to newly arriving species, thus enhancing community invasion resistance. 相似文献
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