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21.
Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae) 总被引:5,自引:0,他引:5
Campbell CS; Wojciechowski MF; Baldwin BG; Alice LA; Donoghue MJ 《Molecular biology and evolution》1997,14(1):81-90
Individual plants of several Amelanchier taxa contain many polymorphic
nucleotide sites in the internal transcribed spacers (ITS) of nuclear
ribosomal DNA (nrDNA). This polymorphism is unusual because it is not
recent in origin and thus has resisted homogenization by concerted
evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the
result of gene flow between two major North American clades resolved by
phylogenetic analysis of ITS sequences. Western North American species plus
A. humilis and A. sanguinea of eastern North America form one clade (A),
and the remaining eastern North American Amelanchier make up clade B. Five
eastern North American taxa are polymorphic at many of the nucleotide sites
where clades A and B have diverged and are thought to be of hybrid origin,
with A. humilis or A. sanguinea as one parent and various members of clade
B as the other parent. Morphological evidence suggests that A. humilis is
one of the parents of one of the polymorphic taxa, a microspecies that we
refer to informally as A. "erecta." Sequences of 21 cloned copies of the
ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical
to A. humilis sequence or to the clade B consensus sequence, or they are
apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier
"erecta" and another polymorphic taxon are suspected to be relatively old
because both grow several hundred kilometers beyond the range of one of
their parents. ITS sequence polymorphisms have apparently persisted in
these two taxa perhaps because of polyploidy and/or agamospermy (asexual
seed production), which are prevalent in the genus.
相似文献
22.
Kaldonski N Perrot-Minnot MJ Dodet R Martinaud G Cézilly F 《Proceedings. Biological sciences / The Royal Society》2009,276(1654):169-176
Manipulation by parasites is a catchy concept that has been applied to a large range of phenotypic alterations brought about by parasites in their hosts. It has, for instance, been suggested that the carotenoid-based colour of acanthocephalan cystacanths is adaptive through increasing the conspicuousness of infected intermediate hosts and, hence, their vulnerability to appropriate final hosts such as fish predators. We revisited the evidence in favour of adaptive coloration of acanthocephalan parasites in relation to increased trophic transmission using the crustacean amphipod Gammarus pulex and two species of acanthocephalans, Pomphorhynchus laevis and Polymorphus minutus. Both species show carotenoid-based colorations, but rely, respectively, on freshwater fish and aquatic bird species as final hosts. In addition, the two parasites differ in the type of behavioural alteration brought to their common intermediate host. Pomphorhynchus laevis reverses negative phototaxis in G. pulex, whereas P. minutus reverses positive geotaxis. In aquaria, trout showed selective predation for P. laevis-infected gammarids, whereas P. minutus-infected ones did not differ from uninfected controls in their vulnerability to predation. We tested for an effect of parasite coloration on increased trophic transmission by painting a yellow-orange spot on the cuticle of uninfected gammarids and by masking the yellow-orange spot of infected individuals with inconspicuous brown paint. To enhance realism, match of colour between painted mimics and true parasite was carefully checked using a spectrometer. We found no evidence for a role of parasite coloration in the increased vulnerability of gammarids to predation by trout. Painted mimics did not differ from control uninfected gammarids in their vulnerability to predation by trout. In addition, covering the place through which the parasite was visible did not reduce the vulnerability of infected gammarids to predation by trout. We discuss alternative evolutionary explanations for the origin and maintenance of carotenoid-based colorations in acanthocephalan parasites. 相似文献
23.
Ponton F Lefevre T Lebarbenchon C Thomas F Loxdale HD Marché L Renault L Perrot-Minnot MJ Biron DG 《Proceedings. Biological sciences / The Royal Society》2006,273(1603):2869-2877
Phylogenetically unrelated parasites often increase the chances of their transmission by inducing similar phenotypic changes in their hosts. However, it is not known whether these convergent strategies rely on the same biochemical precursors. In this paper, we explored such aspects by studying two gammarid species (Gammarus insensibilis and Gammarus pulex; Crustacea: Amphipoda: Gammaridae) serving as intermediate hosts in the life cycle of two distantly related parasites: the trematode, Microphallus papillorobustus and the acanthocephalan, Polymorphus minutus. Both these parasite species are known to manipulate the behaviour of their amphipod hosts, bringing them towards the water surface, where they are preferentially eaten by aquatic birds (definitive hosts). By studying and comparing the brains of infected G. insensibilis and G. pulex with proteomics tools, we have elucidated some of the proximate causes involved in the parasite-induced alterations of host behaviour for each system. Protein identifications suggest that altered physiological compartments in hosts can be similar (e.g. immunoneural connexions) or different (e.g. vision process), and hence specific to the host-parasite association considered. Moreover, proteins required to alter the same physiological compartment can be specific or conversely common in both systems, illustrating in the latter case a molecular convergence in the proximate mechanisms of manipulation. 相似文献
24.
Marieke?Pingen Ramin?Sarrami-Forooshani Annemarie?MJ?Wensing Petra?van Ham Agata?Drewniak Charles?AB?Boucher Teunis?BH?GeijtenbeekEmail author Monique?NijhuisEmail author 《Retrovirology》2014,11(1):113
Background
Different patterns of drug resistance are observed in treated and therapy naïve HIV-1 infected populations. Especially the NRTI-related M184I/V variants, which are among the most frequently encountered mutations in treated patients, are underrepresented in the antiretroviral naïve population. M184I/V mutations are known to have a profound effect on viral replication and tend to revert over time in the new host. However it is debated whether a diminished transmission efficacy of HIV variants with a reduced replication capacity can also contribute to the observed discrepancy in genotypic patterns.As dendritic cells (DCs) play a pivotal role in HIV-1 transmission, we used a model containing primary human Langerhans cells (LCs) and DCs to compare the transmission efficacy M184 variants (HIV-M184V/I/T) to HIV wild type (HIV-WT). As control, we used HIV harboring the NNRTI mutation K103N (HIV-K103N) which has a minor effect on replication and is found at a similar prevalence in treated and untreated individuals.Results
In comparison to HIV-WT, the HIV-M184 variants were less efficiently transmitted to CCR5+ Jurkat T cells by both LCs and DCs. The transmission rate of HIV-K103N was slightly reduced to HIV-WT in LCs and even higher than HIV-WT in DCs. Replication experiments in CCR5+ Jurkat T cells revealed no apparent differences in replication capacity between the mutant viruses and HIV-WT. However, viral replication in LCs and DCs was in concordance with the transmission results; replication by the HIV-M184 variants was lower than replication by HIV-WT, and the level of replication of HIV-K103N was intermediate for LCs and higher than HIV-WT for DCs.Conclusions
Our data demonstrate that drug resistant M184-variants display a reduced replication capacity in LCs and DCs which directly impairs their transmission efficacy. As such, diminished transmission efficacy may contribute to the lower prevalence of drug resistant variants in therapy naive individuals.25.
Phenotypic alterations induced by parasites in their intermediate hosts often result in enhanced trophic transmission to appropriate final hosts. However, such alterations may also increase the vulnerability of intermediate hosts to predation by non-host species. We studied the influence of both infection with 3 different acanthocephalan parasites (Pomphorhynchus laevis, P. tereticollis, and Polymorphus minutus) and the availability of refuges on the susceptibility of the amphipod Gammarus pulex to predation by 2 non-host predators in microcosms. Only infection with P. laevis increased the vulnerability of amphipods to predation by crayfish, Orconectes limosus. In contrast, in the absence of refuges, the selectivity of water scorpions, Nepa cinerea, for infected prey was significant and did not differ according to parasite species. When a refuge was available for infected prey, however, water scorpion selectivity for infected prey differed between parasite species. Both P. tereticollis- and P. laevis-infected gammarids were more vulnerable than uninfected ones, whereas the reverse was true of P. minutus-infected gammarids. These results suggest that the true consequences of phenotypic changes associated with parasitic infection in terms of increased trophic transmission of parasites deserve further assessment. 相似文献
26.
Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high. 相似文献
27.
Haine ER Brondani E Hume KD Perrot-Minnot MJ Gaillard M Rigaud T 《International journal for parasitology》2004,34(10):1137-1146
We investigated the prevalence, transmission mode and fitness effects of infections by obligatory intracellular, microsporidian parasites in the freshwater amphipod Gammarus roeseli. We found three different microsporidia species in this host, all using transovarial (vertical) transmission. All three coexist at different prevalences in two host populations, but bi-infected individuals were rarely found, suggesting no (or very little) horizontal transmission. It is predicted that vertically-transmitted parasites may exhibit sex-specific virulence in their hosts, or they may have either positive or neutral effects on host fitness. All three species differed in their transmission efficiency and infection intensity and our data suggest that these microsporidia exert sex-specific virulence by feminising male hosts. The patterns of infection we found exhibit convergent evolution with those of another amphipod host, Gammarus duebeni. Interestingly, we found that infected females breed earlier in the reproductive season than uninfected females. This is the first study, to our knowledge, to report a positive effect of microsporidian infection on female host reproduction. 相似文献
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30.
Current phylogenetic tree reconstruction methods assume that there is a
single underlying tree topology for all sites along the sequence. The
presence of mosaic sequences due to recombination violates this assumption
and will cause phylogenetic methods to give misleading results due to the
imposition of a single tree topology on all sites. The detection of mosaic
sequences caused by recombination is therefore an important first step in
phylogenetic analysis. A graphical method for the detection of
recombination, based on the least squares method of phylogenetic
estimation, is presented here. This method locates putative recombination
breakpoints by moving a window along the sequence. The performance of the
method is assessed by simulation and by its application to a real data set.
相似文献