Why Wolbachia-induced cytoplasmic incompatibility is so common

Area of Science:

• Evolutionary biology
• Microbial genetics
• Insect pathology

Background:

• Cytoplasmic incompatibility (CI) is a common reproductive manipulation by Wolbachia bacteria, infecting half of insect species.
• Wolbachia infections can reach high frequencies due to CI, but within-population selection doesn't favor CI-inducing variants.
• Despite this, many Wolbachia infections still cause CI, posing an evolutionary puzzle.

Purpose of the Study:

• To investigate the evolutionary forces maintaining cytoplasmic incompatibility (CI) in Wolbachia infections within insect populations.
• To determine whether within-host selection or interspecific spread (clade selection) better explains the persistence of CI-inducing Wolbachia.
• To model the dynamics of Wolbachia acquisition and loss in host species and the evolution of CI-induction.

Main Methods:

• Developed an epidemiological model to simulate Wolbachia acquisition and loss in host species.
• Analyzed factors influencing Wolbachia frequency and the incidence of CI-inducing variants.
• Examined evidence for recent host-species acquisition, spatial spread, and rapid evolution of CI-inducing loci in Wolbachia.

Main Results:

• Clade selection, or preferential spread to new host species, is a more plausible explanation for CI persistence than within-population selection.
• CI-causing Wolbachia lineages benefit from increased equilibrium frequencies and resilience to changing host conditions.
• Model outputs provide simple expressions for Wolbachia infection incidence and the fraction of infections causing CI.

Conclusions:

• Differential interspecific spread plays a crucial role in maintaining CI in Wolbachia infections.
• The recent acquisition of hosts and rapid evolution of CI loci support the importance of clade selection.
• Understanding these dynamics is key to explaining the widespread prevalence of CI in insect-borne alphaproteobacteria.