PubMed · 8623607
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P Boileau, G Walch. 1995. [Adaptability and modulation in shoulder prosthesis].. https://pubmed.ncbi.nlm.nih.gov/8623607/
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We present the first genome-wide study of recent evolution in Culex pipiens species complex focusing on the genomic extent, functional targets and likely causes of global and local adaptations. We resequenced pooled samples of six populations of C. pipiens and two populations of the outgroup Culex torrentium. We used principal component analysis to systematically study differential natural selection across populations and developed a phylogenetic scanning method to analyse admixture without haplotype data. We found evidence for the prominent role of geographical distribution in shaping population structure and specifying patterns of genomic selection. Multiple adaptive events, involving genes implicated with autogeny, diapause and insecticide resistance were limited to specific populations. We estimate that about 5-20% of the genes (including several histone genes) and almost half of the annotated pathways were undergoing selective sweeps in each population. The high occurrence of sweeps in non-genic regions and in chromatin remodelling genes indicated the adaptive importance of gene expression changes. We hypothesize that global adaptive processes in the C. pipiens complex are potentially associated with South to North range expansion, requiring adjustments in chromatin conformation. Strong local signature of adaptation and emergence of hybrid bridge vectors necessitate genomic assessment of populations before specifying control agents.
Stationary-phase mutation in microbes can produce selected ('adaptive') mutants preferentially. In one system, this occurs via a distinct, recombination-dependent mechanism. Two points of controversy have surrounded these adaptive reversions of an Escherichia coli lac mutation. First, are the mutations directed preferentially to the selected gene in a Lamarckian manner? Second, is the adaptive mutation mechanism specific to the F plasmid replicon carrying lac? We report that lac adaptive mutations are associated with hypermutation in unselected genes, in all replicons in the cell. The associated mutations have a similar sequence spectrum to the adaptive reversions. Thus, the adaptive mutagenesis mechanism is not directed to the lac genes, in a Lamarckian manner, nor to the F' replicon carrying lac. Hypermutation was not found in non-revertants exposed to selection. Therefore, the genome-wide hypermutation underlying adaptive mutation occurs in a differentiated subpopulation. The existence of mutable subpopulations in non-growing cells is important in bacterial evolution and could be relevant to the somatic mutations that give rise to cancers in multicellular organisms.
Both theory and data suggest that malaria parasites divert resources from within-host replication to the production of transmission stages (gametocytes) when conditions deteriorate. Increased investment into transmission stages should therefore follow subcurative treatment with antimalarial drugs, but relevant clinical studies necessarily lack adequate control groups. We therefore carried out controlled experiments to test this hypothesis, using a rodent malaria (Plasmodium chabaudi) model. Infections treated with a subcurative dose of the antimalarial chloroquine showed an earlier peak and a greater rate of gametocyte production relative to untreated controls. These alterations led to correlated changes in infectivity to mosquitoes, with the consequence that chloroquine treatment had no effect on the proportion of mosquitoes infected. Treatment of human malaria commonly does not result in complete parasite clearance. If surviving parasites produce compensatory increases in their rate of gametocyte production similar to those reported here, such treatment may have minimal effect on decreasing, and may actually increase, transmission. Importantly, if increased investment in transmission is a generalized stress response, the effect might be observed following a variety of antimalarial treatments, including other drugs and potential vaccines. Similar parasite life history counter-adaptations to intervention strategies are likely to occur in many disease-causing organisms.