Abstract
Wolbachia is a well-known endosymbiotic, strictly cytoplasmic bacterium. It establishes complex cytonuclear relations that are not necessarily deleterious to its host, but that often result in reproductive alterations favoring bacterial transmission. Among these alterations, a common one is the cytoplasmic incompatibility (CI) that reduces the number of descendants in certain crosses between infected and non-infected individuals. This CI induced by Wolbachia appears in the hybrid zone that the grasshoppers Chorthippus parallelus parallelus (Cpp) and C. p. erythropus (Cpe) form in the Pyrenees: a reputed model in evolutionary biology. However, this cytonuclear incompatibility is the result of sophisticated processes of the co-divergence of the genomes of the bacterial strains and the host after generations of selection and coevolution. Here we show how these genome conflicts have resulted in a finely tuned adjustment of the bacterial strain to each pure orthopteroid taxon, and the striking appearance of another, newly identified recombinant Wolbachia strain that only occurs in hybrid grasshoppers. We propose the existence of two superimposed hybrid zones: one organized by the grasshoppers, which overlaps with a second, bacterial hybrid zone. The two hybrid zones counterbalance one another and have evolved together since the origin of the grasshopper's hybrid zone.
Highlights
Wolbachia is a well-known endosymbiotic alphaproteobacterium that is able to modify the reproduction of infected individuals in diverse ways: male feminizing and killing, induced parthenogenesis, cytoplasmic incompatibility (CI), etc
The existence of newly identified genetic markers allows us to characterize with greater precision the genetic diversity, potential recombination phenomena and the geographical distribution of Wolbachia through the Chorthippus parallelus hybrid zone
New data from the Wolbachia MLST system, obtained following Baldo et al (2006b), confirmed the double infection by F and B supergroups and its distribution in C. parallelus. It revealed the great diversity at the supergroup level. These data confirmed the presence of two F bacterial types on both sides of the hybrid zone, as Zabal-Aguirre et al (2010) suggested
Summary
Wolbachia is a well-known endosymbiotic alphaproteobacterium that is able to modify the reproduction (and, in some cases, the behavior) of infected individuals in diverse ways: male feminizing and killing, induced parthenogenesis, cytoplasmic incompatibility (CI), etc. This additional example of cytonuclear dialogue between the endosymbiotic Wolbachia and the Cp genome indicates a close coevolution of the two genomes that we can summarize as specific biogeographical patterns of infection that fit well with the pure Cpp, Cpe or hybrid condition of the grasshoppers (specific bacterial strains preferentially infecting each taxa).
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