Symbiosis and horizontal gene transfer promote herbivory in the megadiverse leaf beetles

Among the key adaptations for herbivory are plant cell wall degrading enzymes (PCWDEs) that break down the fastidious polymers in the cell wall and grant access to the nutritious cell content. While largely absent from the non-herbivorous ancestors of beetles, such PCWDEs were occasionally acquired via horizontal gene transfer (HGT) or by the uptake of digestive symbionts.

However, the macro-evolutionary dynamics of PCWDEs and their impact on evolutionary transitions in herbivorous insects remained poorly understood. Through genomic and transcriptomic analyses of 74 leaf beetle species and 50 symbionts, we show that multiple independent events of microbe-to-beetle horizontal gene transfer and specialized symbioses drove convergent evolutionary innovations in approximately 21,000 and 13,500 leaf beetle species, respectively.