Intra-lineage microevolution of Wolbachia leads to the emergence of new cytoplasmic incompatibility patterns

Area of Science:

• * Molecular biology
• * Evolutionary genetics
• * Vector-borne disease research

Background:

• * Culex pipiens mosquitoes are significant global vectors for arboviruses, filarial nematodes, and avian malaria.
• * The endosymbiotic bacteria Wolbachia induce cytoplasmic incompatibility (CI) in these mosquitoes, affecting embryo viability.
• * Wolbachia strains in Culex pipiens (wPip) exhibit complex CI patterns linked to variations in cidA and cidB genes.

Purpose of the Study:

• * To investigate the real-time evolution of cytoplasmic incompatibility (CI) in Culex pipiens mosquitoes.
• * To determine the genetic basis for changes in CI patterns and compatibility types.
• * To validate the toxin-antidote (TA) model for CI in natural Wolbachia-host interactions.

Main Methods:

• * Longitudinal study involving repeated crosses of Culex isofemale lines over 17 years.
• * Genomic analysis of Wolbachia cid genes (cidA and cidB) in different mosquito lines.
• * Comparative sequence analysis of toxin and antidote binding interfaces.

Main Results:

• * Observed the emergence of a novel CI compatibility type in real time.
• * Linked this new type to the loss of specific cidA gene copies in wPip genomes.
• * Demonstrated that loss of certain cidA genes resulted in loss of compatibility, with evidence of recombination driving these changes.

Conclusions:

• * The study provides strong in natura support for the toxin-antidote (TA) model of CI.
• * Recombination, rather than point mutations, appears to be a key driver of rapid CI evolution in wPip.
• * Understanding these genetic mechanisms is crucial for controlling vector populations and disease transmission.