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911.
Dostál P 《The American naturalist》2011,177(5):655-667
The invasion success of introduced plants is frequently explained as a result of competitive interactions with native flora. Although previous theory and experiments have shown that plants are largely equivalent in their competitive effects on each other, competitive nonequivalence is hypothesized to occur in interactions between native and invasive species. Small overlap in resource use with unrelated native species, improved competitiveness, and production of novel allelochemicals are all believed to contribute to the invasiveness of introduced species. I tested all three assumptions in a common-garden experiment by examining the effect of plant origin and relatedness on competition intensity. Competitive interactions were explored within 12 triplets, each consisting of an invasive species, a native congeneric (or confamilial) species, and a native heterogeneric species that are likely to interact in the field. Plants were grown in pots alone or in pairs and in the absence or the presence of activated carbon to control for allelopathy. I found that competition intensity was not influenced by the relatedness or origin of competing neighbors. Although some exotic species may benefit from size advantages and species-specific effects in competitive interactions, none of the three mechanisms investigated is likely to be a principal driver of their invasiveness. 相似文献
912.
913.
Dale A. Casamatta Chelsea D. Villanueva Alyssa D. Garvey Holly S. Stocks Melissa Vaccarino Petr Dvořák Petr Hašler Jeffrey R. Johansen 《Journal of phycology》2020,56(2):425-436
The Nostocales is a monophyletic, heterocytous lineage of cyanobacteria capable of akinete production and division in multiple planes, depending upon family-level clade. While present in a variety of ecosystems, the diversity of the Nostocales has been poorly elucidated. Due to environmentally -induced phenotypic plasticity, morphology alone is often insufficient to determine the true phylogenetic placement of these taxa. In order to bridge this gap, taxonomists now employ the polyphasic approach, combining methods such as morphological analysis, phylogenetic analysis based on DNA sequence and genetic identity based on ribosomal genes, and secondary structure of the 16S-23S ITS and 16S rRNA gene sequences, as well as ecological characterization. Using this combined approach, a new genus and species (Reptodigitus chapmanii gen. et sp. nov.) isolated from the St. Johns River (Jacksonville, Florida, USA) within the Nostocales is herein described. Phylogenetic analyses place this taxon within the Hapalosiphonaceae, sister to the clade containing Fischerella, Hapalosiphon, and Westiellopsis. The 16S-23S ITS secondary folding structure analysis also supports the erection of this new genus. 相似文献
914.
Masha T. van der Sande Helge Bruelheide Wayne Dawson Jürgen Dengler Franz Essl Richard Field Sylvia Haider Mark van Kleunen Holger Kreft Joern Pagel Jan Pergl Oliver Purschke Petr Pyek Patrick Weigelt Marten Winter Fabio Attorre Isabelle Aubin Erwin Bergmeier Milan Chytrý Matteo Dainese Michele De Sanctis Jaime Fagundez Valentin Golub Greg R. Guerin Alvaro G. Gutirrez Ute Jandt Florian Jansen Borja Jimnez‐Alfaro Jens Kattge Elizabeth Kearsley Stefan Klotz Koen Kramer Marco Moretti Ülo Niinemets Robert K. Peet Josep Penuelas Petr Petík Peter B. Reich Brody Sandel Marco Schmidt Maria Sibikova Cyrille Violle Timothy J. S. Whitfeld Thomas Wohlgemuth Tiffany M. Knight 《Global Ecology and Biogeography》2020,29(2):281-294
915.
916.
The North American ecological species
Daphnia
pulicaria
and
Daphnia
pulex
are thought to have diverged from a common ancestor by adaptation to sympatric but ecologically distinct lake and pond habitats respectively. Based on mtDNA relationships, European
D
. pulicaria
is considered a different species only distantly related to its North American counterpart, but both species share a lactate dehydrogenase (Ldh) allele F supposedly involved in lake adaptation in North America, and the same allele is also carried by the related Holarctic
Daphnia
tenebrosa
. The correct inference of the species’ ancestral relationships is therefore critical for understanding the origin of their adaptive divergence. Our species tree inferred from unlinked nuclear loci for
D
. pulicaria
and
D
. pulex
resolved the European and North American
D
. pulicaria
as sister clades, and we argue that the discordant mtDNA gene tree is best explained by capture of
D
. pulex
mtDNA by
D
. pulicaria
in North America. The Ldh gene tree shows that F-class alleles in
D
. pulicaria
and
D
. tenebrosa
are due to common descent (as opposed to introgression), with
D
. tenebrosa
alleles paraphyletic with respect to
D
. pulicaria
alleles. That
D
. tenebrosa
still segregates the ancestral and derived amino acids at the two sites distinguishing the pond and lake alleles suggests that
D
. pulicaria
inherited the derived states from the
D
. tenebrosa
ancestry. Our results suggest that some adaptations restricting the gene flow between
D
. pulicaria
and
D
. pulex
might have evolved in response to selection in ancestral environments rather than in the species’ current sympatric habitats. The Arctic (
D
. tenebrosa
) populations are likely to provide important clues about these issues. 相似文献
917.
918.
We report the distribution and disease level of downy mildew on lettuce (Lactuca sativa) and virulence variation in populations of its causal agent (Bremia lactucae) in the Czech Republic during the period 1999–2011. Disease incidence was not high; among a total of 92 different localities surveyed, 43.4% of them were infected by lettuce downy mildew at least once during the whole period. However, among individual years, differences were found in disease incidence that ranged from 4.8% (2009) to 66.7% (2004). A total of 128 isolates of B. lactucae collected from infected leaf samples in 35 different localities during the surveying period were included in the virulence analysis. Virulence was examined on a set of 19 differential genotypes of Lactuca sativa and Lactuca serriola (EU‐A test set). Isolates exhibited quite a broad variation in virulence to individual Lactuca differential genotypes. Eighteen of 19 virulence factors (v‐factors) tested were present in the samples. The most frequently detected factors were v1–4, v5/8, v6, v7, v10–14, v16, v36 and v38; factor v17 was not found. The most pronounced temporal shift was recorded for factors v36 and v38 whose frequency increased during the studied period. V‐factors 15, 17, 18 and 37 were present in low frequencies in a pathogen population, and their corresponding gene (Dm15) or resistance factors (R17, R18 and R37) may have the best potential for resistance breeding in the Czech Republic. Broad diversity of v‐phenotypes (63 different ones) was identified during the study period. The numbers of v‐factors per v‐phenotype (resp. isolate) varied within a range of 5–15. Within the 128 analysed isolates, only 9 v‐phenotypes were recorded repeatedly (three or more times). Possible reasons of recorded virulence variation are discussed. 相似文献
919.
Josef Urban Kateřina Holušová Ladislav Menšík Jan Čermák Petr Kantor 《Trees - Structure and Function》2013,27(1):97-110
Research related to the allometric relationships of tree height and projected tree crown area to diameter at breast height was conducted to look at the biological suitability and timber production potential of Douglas fir under the conditions present in central Europe. The dependence of allometric relationships on soil nutrient conditions were described in forest stands of Douglas fir and Norway spruce. The studied sites were climatically similar but differed in soil nutrient availability. A significant difference was found in the allometric relationships of Norway spruce trees from the nutrient poor and nutrient rich site. In contrast to the Norway spruce, there was no significant effect of site fertility on allometric relationships for Douglas fir suggesting that its allocation patterns were less sensitive to site nutrient conditions. Stem growth increment, which was measured weekly during two consecutive seasons for both species, was related to the weather conditions and available soil moisture. Stem growth of Douglas fir began about 2 weeks earlier than in the Norway spruce at both sites. At the nutrient rich site, most of the stem growth of both species occurred at the beginning of the season, while growth at the other site was more evenly distributed throughout the season. Data obtained in this study will be useful for modeling stem growth and analysis of water use efficiency of these two tree species. 相似文献
920.
Simon Renny‐Byfield Ales Kovarik Laura J. Kelly Jiri Macas Petr Novak Mark W. Chase Richard A. Nichols Mahesh R. Pancholi Marie‐Angele Grandbastien Andrew R. Leitch 《The Plant journal : for cell and molecular biology》2013,74(5):829-839
Recent advances have highlighted the ubiquity of whole‐genome duplication (polyploidy) in angiosperms, although subsequent genome size change and diploidization (returning to a diploid‐like condition) are poorly understood. An excellent system to assess these processes is provided by Nicotiana section Repandae, which arose via allopolyploidy (approximately 5 million years ago) involving relatives of Nicotiana sylvestris and Nicotiana obtusifolia. Subsequent speciation in Repandae has resulted in allotetraploids with divergent genome sizes, including Nicotiana repanda and Nicotiana nudicaulis studied here, which have an estimated 23.6% genome expansion and 19.2% genome contraction from the early polyploid, respectively. Graph‐based clustering of next‐generation sequence data enabled assessment of the global genome composition of these allotetraploids and their diploid progenitors. Unexpectedly, in both allotetraploids, over 85% of sequence clusters (repetitive DNA families) had a lower abundance than predicted from their diploid relatives; a trend seen particularly in low‐copy repeats. The loss of high‐copy sequences predominantly accounts for the genome downsizing in N. nudicaulis. In contrast, N. repanda shows expansion of clusters already inherited in high copy number (mostly chromovirus‐like Ty3/Gypsy retroelements and some low‐complexity sequences), leading to much of the genome upsizing predicted. We suggest that the differential dynamics of low‐ and high‐copy sequences reveal two genomic processes that occur subsequent to allopolyploidy. The loss of low‐copy sequences, common to both allopolyploids, may reflect genome diploidization, a process that also involves loss of duplicate copies of genes and upstream regulators. In contrast, genome size divergence between allopolyploids is manifested through differential accumulation and/or deletion of high‐copy‐number sequences. 相似文献