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Recombination operates at the evolutionary scale: reticulate evolution

The presence of hybrid genotypes in T. cruzi natural populations has long been hypothesized.61-64 The potentiality of genetic recombination in this species has been experimentally demonstrated by Gaunt et al.65 These experimental hybrids have been obtained from parental genotypes that are genetically only closely related. They seem to be generated by fusion of diploid parents followed by genomic erosion slowly returning to a diploid state. Natural hybrids seem to be of a different nature. They are predominantly diploid and can be the result of hybridization between distantly related parental genotypes.66 Different scenarios and genealogies have been proposed to explain the generation of the currently observed natural hybrids in T. cruzi}1 This will be detailed further (see: Evolutionary origin of the hybrid near-clades). At this step, a number of important points about recombination in T. cruzi should be underlined: (1) these events are exceptional in this parasite’s natural populations. By definition, frequent genetic exchange would be incompatible with the strong inhibition of genetic recombination evidenced by linkage disequilibrium. (2) Once generated, the hybrid genotypes are stabilized by clonal propagation and behave like genetic clones. They have been recurrently observed unchanged over long periods of time and large geographical areas. (3) These natural hybrid clones are widespread in domestic chagasic cycles and could represent a specific adaptation to these transmission cycles, in which they behave like successful genotypes.

 
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