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1.
J Daugherty TM Evans T Skillom LE Watson NP Money 《Fungal genetics and biology : FG & B》1998,24(3):354-363
Classical studies on spore release within the Saprolegniaceae (Oomycetes) led to the proposition that different mechanisms of sporangial emptying represent steps in an evolutionary transition series. We have reevaluated this idea in a phylogenetic framework using internal transcribed spacer sequences of four genera. These data were compared with the response to osmotic stress exhibited by each taxon. Saprolegnia emerges as the most basal genus, sister to Achlya, Thraustotheca, and Dictyuchus. Achlya and Thraustotheca are most closely related, while Dictyuchus appears to have evolved along a separate evolutionary lineage. The resulting phylogenetic framework is consistent with the idea that the mechanism of sporangial emptying exhibited by Saprolegnia represents the plesiomorphic condition from which the other mechanisms were derived independently. These alternative mechanisms of spore release may have resulted from a small number of mutations that inhibited axonemal development and altered the temporal and spatial expression of lytic enzymes that degrade the sporangial wall. Copyright 1998 Academic Press. 相似文献
2.
Krasnov BR Stanko M Matthee S Laudisoit A Leirs H Khokhlova IS Korallo-Vinarskaya NP Vinarski MV Morand S 《Oecologia》2011,166(4):1099-1110
We studied the co-occurrence of flea species in infracommunities of 16 rodents from four regions (South Africa, Tanzania,
central Europe and western Siberia) using null models, and predicted that flea co-occurrences will be expressed more strongly
in male than in female hosts. We examined patterns of co-occurrence (measured as the C score) in infracommunities of fleas that are parasitic on male and female hosts by comparing co-occurrence frequencies with
those expected by chance. When a significant degree of nonrandomness in flea co-occurrences was detected, it indicated aggregative
infracommunity structure. In Tanzanian rodents, no significant flea co-occurrences were detected in either male or female
hosts. In a South African rodent, significant flea co-occurrences were not detected in males, but were found in females in
some localities. In Palaearctic rodents, significant nonrandomness was detected either equally for males and females or more
frequently in males than in females. Meta-analyses demonstrated that the frequency of the detection of nonrandomness in flea
co-occurrences was significantly higher in male than in female hosts. The values of the standardized effect size (SES) for
the C score differed significantly among host species, but not between host genders. When the Palaearctic hosts were analyzed separately,
the effects of both host gender and species appeared to be significant, with the SES values for the C score in males being smaller than those in females. The strength of the gender difference in the manifestation of flea community
structure increased with increasing gender difference in flea species richness, and with decreasing gender difference in flea
prevalence for the Palaearctic hosts. We conclude that male hosts are the main drivers of flea infracommunity structure. However,
the manifestation of gender bias in flea community structure varies among host species, and is likely determined by the pattern
of species-specific spatial behavior. 相似文献
3.
Fasinu Pius S Tekwani Babu L Nanayakkara NP Dhammika Avula Bharathi Herath HMT Bandara Wang Yan-Hong Adelli Vijender R Elsohly Mahmoud A Khan Shabana I Khan Ikhlas A Pybus Brandon S Marcsisin Sean R Reichard Gregory A McChesney James D Walker Larry A 《Malaria journal》2014,13(1):1-12
Given the threat of resistance of human malaria parasites, including to artemisinin derivatives, new agents are needed. Chloroquine (CQ) has been the most widely used anti-malarial, and new analogs (CQAns) presenting alkynes and side chain variations with high antiplasmodial activity were evaluated. Six diaminealkyne and diaminedialkyne CQAns were evaluated against CQ-resistant (CQ-R) (W2) and CQ-sensitive (CQ-S) (3D7) Plasmodium falciparum parasites in culture. Drug cytotoxicity to a human hepatoma cell line (HepG2) evaluated, allowed to calculate the drug selectivity index (SI), a ratio of drug toxicity to activity in vitro. The CQAns were re-evaluated against CQ-resistant and -sensitive P. berghei parasites in mice using the suppressive test. Docking studies with the CQAns and the human (Hss LDH) or plasmodial lactate dehydrogenase (Pf LDH) enzymes, and, a β-haematin formation assay were performed using a lipid as a catalyst to promote crystallization in vitro. All tested CQAns were highly active against CQ-R P. falciparum parasites, exhibiting half-maximal inhibitory concentration (IC50) values below 1 μΜ. CQAn33 and CQAn37 had the highest SIs. Docking studies revealed the best conformation of CQAn33 inside the binding pocket of Pf LDH; specificity between the residues involved in H-bonds of the Pf LDH with CQAn37. CQAn33 and CQAn37 were also shown to be weak inhibitors of Pf LDH. CQAn33 and CQAn37 inhibited β-haematin formation with either a similar or a 2-fold higher IC50 value, respectively, compared with CQ. CQAn37 was active in mice with P. berghei, reducing parasitaemia by 100%. CQAn33, -39 and -45 also inhibited CQ-resistant P. berghei parasites in mice, whereas high doses of CQ were inactive. The presence of an alkyne group and the size of the side chain affected anti-P. falciparum activity in vitro. Docking studies suggested a mechanism of action other than Pf LDH inhibition. The β-haematin assay suggested the presence of an additional mechanism of action of CQAn33 and CQAn37. Tests with CQAn34, CQAn37, CQAn39 and CQAn45 confirmed previous results against P. berghei malaria in mice, and CQAn33, 39 and 45 were active against CQ-resistant parasites, but CQAn28 and CQAn34 were not. The result likely reflects structure-activity relationships related to the resistant phenotype. 相似文献
4.
Boris R. Krasnov Maxim V. Vinarski Natalia P. Korallo-Vinarskaya David Mouillot Robert Poulin 《Oecologia》2009,160(1):175-185
Within a community, the abundance of any given species depends in large part on a network of direct and indirect, positive
and negative interactions with other species, including shared enemies. In communities where experimental manipulations are
often impossible (e.g., parasite communities), census data can be used to evaluate the strength or frequency of positive and
negative associations among species. In ectoparasite communities, competitive associations can arise because of limited space
or food, but facilitative associations can also exist if one species suppresses host immune defenses. In addition, positive
associations among parasites could arise merely due to shared preferences for the same host, without any interaction going
on. We used census data from 28 regional surveys of gamasid mites parasitic on small mammals throughout the Palaearctic, to
assess how the abundance of individual mite species is influenced by the abundance and diversity of other mite species on
the same host. After controlling for several confounding variables, the abundance of individual mite species was generally
positively correlated with the combined abundances of all other mite species in the community. This trend was confirmed by
meta-analysis of the results obtained for separate mite species. In contrast, there were generally no consistent relationships
between the abundance of individual mite species and either the species richness or taxonomic diversity of the community in
which they occur. These patterns were independent of mite feeding mode. Our results indicate either that synergistic facilitative
interactions among mites increase the host’s susceptibility to further attacks (e.g., via immunosuppression) and lead to different
species all having increased abundance on the same host, or that certain characteristics make some host species preferred
habitats for many parasite species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
Boris R. Krasnov David Mouillot Irina S. Khokhlova Natalia P. Korallo-Vinarskaya 《International journal for parasitology》2010,40(7):807-817
Different host species harbour parasite faunas that are anywhere from very similar to very different in species composition. A priori, the similarity in the parasite faunas of any two host species should decrease with increases in either the phylogenetic distance, the distinctness of the environments occupied or the geographical distance between these hosts. We tested these predictions using extensive data on the faunas of fleas (Insecta: Siphonaptera) and gamasid mites (Acari: Parasitiformes) parasitic on rodents across the Palaearctic. For each pair of host species, we computed the similarity in parasite faunas based on both species composition as well as the phylogenetic and/or taxonomic distinctness of parasite species. Phylogenetic distances between hosts were based on patristic distances through a rodent phylogeny, geographic distances were computed from geographic range data, and environmental dissimilarity was measured from the average climatic and vegetation scores of each host range. Using multiple regressions on distance matrices to assess the separate explanatory power of each of the three dependent variables, environmental dissimilarity between the ranges of host species emerged as the best predictor of dissimilarity between parasite faunas, especially for fleas; in the case of mites, phylogenetic distance between host species was also important. A closer look at the data indicates that the flea and mite faunas of two hosts inhabiting different environments are always different, whilst hosts living in similar environments can have either very similar or dissimilar parasite faunas. Additional tests showed that dissimilarity in flea or mite faunas between host geographic ranges was best explained by dissimilarity in vegetation, followed by dissimilarity in climatic conditions. Thus, external environmental factors may play greater roles than commonly thought in the evolution of host-parasite associations. 相似文献
6.
Elizabeth?M.?WarburtonEmail author Luther?van der?Mescht Michal?Stanko Maxim?V.?Vinarski Natalia?P.?Korallo-Vinarskaya Irina?S.?Khokhlova Boris?R.?Krasnov 《Oecologia》2017,184(2):507-520
Beta-diversity of biological communities can be decomposed into (a) dissimilarity of communities among units of finer scale within units of broader scale and (b) dissimilarity of communities among units of broader scale. We investigated compositional, phylogenetic/taxonomic and functional beta-diversity of compound communities of fleas and gamasid mites parasitic on small Palearctic mammals in a nested hierarchy at two spatial scales: (a) continental scale (across the Palearctic) and (b) regional scale (across sites within Slovakia). At each scale, we analyzed beta-diversity among smaller units within larger units and among larger units with partitioning based on either geography or ecology. We asked (a) whether compositional, phylogenetic/taxonomic and functional dissimilarities of flea and mite assemblages are scale dependent; (b) how geographical (partitioning of sites according to geographic position) or ecological (partitioning of sites according to habitat type) characteristics affect phylogenetic/taxonomic and functional components of dissimilarity of ectoparasite assemblages and (c) whether assemblages of fleas and gamasid mites differ in their degree of dissimilarity, all else being equal. We found that compositional, phylogenetic/taxonomic, or functional beta-diversity was greater on a continental rather than a regional scale. Compositional and phylogenetic/taxonomic components of beta-diversity were greater among larger units than among smaller units within larger units, whereas functional beta-diversity did not exhibit any consistent trend regarding site partitioning. Geographic partitioning resulted in higher values of beta-diversity of ectoparasites than ecological partitioning. Compositional and phylogenetic components of beta-diversity were higher in fleas than mites but the opposite was true for functional beta-diversity in some, but not all, traits. 相似文献
7.
Maxim V. Vinarski Natalia P. Korallo-Vinarskaya Georgy I. Shenbrot Elizabeth M. Warburton Elena N. Surkova Irina S. Khokhlova Boris R. Krasnov 《Ecological Entomology》2020,45(2):321-332
1. This study tested the relationships between the probability of pairwise species co-occurrence and pairwise dissimilarity in their traits in infracommunities (across assemblages harboured by conspecific individual hosts within a locality), component communities (across assemblages harboured by host species within a locality), and compound communities (across assemblages in different localities) of fleas and gamasid mites parasitic on small mammals in Western Siberia. 2. A significant, albeit weak, tendency was found for flea communities harboured by conspecific host individuals, host species, and host communities to be composed of similar species. No relationship between the probability of co-occurrence and trait dissimilarity was detected for mite communities at any hierarchical scale. 3. For fleas, this study explained the link between positive co-occurrence and trait dissimilarity by a process resembling environmental filtering realised mainly via host traits for infracommunities and component communities and via off-host environment for compound communities, thus suggesting that the identical shape of the relationships between co-occurrence and trait dissimilarity at different scales was driven by different mechanisms. 4. The explanation of the lack of this relationship in mites included: (i) the paucity of the subset of mite traits used in this study and its potential inadequacy for the question at hand; and (ii) possible masking of the effect induced by one trait on co-occurrence owing to the lack of this effect induced by another trait(s). 5. Caution is recommended regarding the compilation of a dataset involving multiple traits, its analysis, and the interpretation of the results. 相似文献
8.
Natalia P. Korallo-Vinarskaya Boris R. Krasnov Maxim V. Vinarski Georgy I. Shenbrot David Mouillot Robert Poulin 《Evolutionary ecology》2009,23(3):329-345
There is substantial variability among populations of the same species in basic features such as abundance or niche breadth,
and it is unclear to what extent these are true species traits as opposed to the product of local environmental factors. In
parasites, abundance and niche breadth, i.e. host specificity, show repeatability among different populations of the same
species, but may also be influenced by external forces, depending on the parasite taxa studied. We tested whether the abundance
and host specificity of gamasid mites parasitic on small mammals from 26 different geographic regions of the Palaearctic,
are species-specific or instead determined by host identity and/or parameters of the biotic and abiotic environment. Values
of abundance and host specificity (measured as the number of host species used) were significantly more similar among populations
of the same mite species than among different mite species; despite also showing consistency within particular host species
or regions independently of mite species identity, both abundance and the number of host species used appear to be true mite
species traits. In contrast, the taxonomic distinctness of host species used by a mite showed little repeatability among populations
of the same mite species, and appears mostly determined by the local pool of available host species. Within given mite species,
all three variables (abundance, number of host species used, and their taxonomic distinctness) covaried to some extent with
one or more environmental factors (e.g., nature of the local host assemblage, temperature, precipitation) across geographical
regions, but there was no universal pattern among results from different mite species. These results are similar to those
obtained earlier on other taxa, e.g. fleas, and suggest that there are general laws acting on spatial patterns of parasite
abundance and host specificity. 相似文献
9.
Krasnov Boris R. Vinarski Maxim V. Korallo-Vinarskaya Natalia P. Khokhlova Irina S. 《Oecologia》2020,192(4):1057-1071
Oecologia - We studied compositional turnover in communities of fleas and mites harboured by small mammals using zeta diversity metric (similarity between multiple communities) and asked whether... 相似文献
10.
KH Richau RL Kudahettige P Pujic NP Kudahettige A Sellstedt 《Journal of biosciences》2013,38(4):703-712
The actinorhizal bacterium Frankia expresses nitrogenase and can therefore convert molecular nitrogen into ammonia and the by-product hydrogen. However, nitrogenase is inhibited by oxygen. Consequently, Frankia and its actinorhizal hosts have developed various mechanisms for excluding oxygen from their nitrogen-containing compartments. These include the expression of oxygen-scavenging uptake hydrogenases, the formation of hopanoid-rich vesicles, enclosed by multi-layered hopanoid structures, the lignification of hyphal cell walls, and the production of haemoglobins in the symbiotic nodule. In this work, we analysed the expression and structure of the so-called uptake hydrogenase (Hup), which catalyses the in vivo dissociation of hydrogen to recycle the energy locked up in this ‘waste’ product. Two uptake hydrogenase syntons have been identified in Frankia: synton 1 is expressed under free-living conditions while synton 2 is expressed during symbiosis. We used qPCR to determine synton 1 hup gene expression in two Frankia strains under aerobic and anaerobic conditions. We also predicted the 3D structures of the Hup protein subunits based on multiple sequence alignments and remote homology modelling. Finally, we performed BLAST searches of genome and protein databases to identify genes that may contribute to the protection of nitrogenase against oxygen in the two Frankia strains. Our results show that in Frankia strain ACN14a, the expression patterns of the large (HupL1) and small (HupS1) uptake hydrogenase subunits depend on the abundance of oxygen in the external environment. Structural models of the membrane-bound hydrogenase subunits of ACN14a showed that both subunits resemble the structures of known [NiFe] hydrogenases (Volbeda et al. 1995), but contain fewer cysteine residues than the uptake hydrogenase of the Frankia DC12 and Eu1c strains. Moreover, we show that all of the investigated Frankia strains have two squalene hopane cyclase genes (shc1 and shc2). The only exceptions were CcI3 and the symbiont of Datisca glomerata, which possess shc1 but not shc2. Four truncated haemoglobin genes were identified in Frankia ACN14a and Eu1f, three in CcI3, two in EANpec1 and one in the Datisca glomerata symbiont (Dg). 相似文献