Symbiont replacements reset the co-evolutionary relationship between insects and their heritable bacteria

Area of Science:

• Insect-microbe interactions
• Evolutionary genomics
• Symbiosis

Background:

• Auchenorrhynchan insects rely on bacterial symbionts for nutrition, which undergo genome reduction.
• Host insects must support or replace symbionts with reduced cellular functions.
• Mechanisms of host adaptation to symbiont replacement are not fully understood.

Purpose of the Study:

• To comparatively investigate host-support mechanisms in two Auchenorrhyncha species: Homalodisca vitripennis (GWSS) and Macrosteles quadrilineatus (ALF).
• To understand how symbiont replacement influences host genome evolution and co-evolutionary processes.

Main Methods:

• Comparative genomic analysis of host insects and their bacterial symbionts.
• Identification of host genes involved in symbiont support.
• Analysis of gene duplication, horizontal gene transfer, and mitochondrial gene co-option.

Main Results:

• Both GWSS and ALF evolved novel host-support mechanisms, including horizontal gene transfer and gene duplication.
• GWSS, which replaced an ancestral symbiont (Nasuia) with Baumannia, exhibits fewer support systems for essential bacterial processes compared to ALF.
• Host support for Baumannia in GWSS is limited and tailored to the symbiont's expanded capabilities.

Conclusions:

• Symbiont replacement significantly shapes host genome evolution and the co-evolutionary trajectory.
• Hosts develop diverse strategies to integrate and support symbionts, adapting to symbiont genome size and capabilities.
• The study highlights the dynamic interplay between insect hosts and their microbial partners.