Evolutionary history of tyrosine-supplementing endosymbionts in pollen-feeding Dasytinae (Coleoptera: Melyridae) beetles

Dasytinae (Coleoptera: Melyridae) beetles carry as-yet functionally uncharacterized bacteriome-localized symbionts. This lack of information is surprising for a beetle family of this size and potential influence on ecosystem services. Hence, we investigated 58 species of Melyridae for the presence of bacterial symbionts by a combination of high-throughput 16S rRNA gene based microbiota profiling, diagnostic PCRs, genome sequencing, and fluorescence in situ hybridization. We reconstructed a molecular phylogeny of the hosts to elucidate the origin and evolutionary dynamics of the association with nutritional symbionts, supporting a single acquisition of bacteriome-localized symbionts in Dasytinae and multiple loss events. In order to gain functional insights, we sequenced the symbiont genomes of 20 host species, revealing tyrosine biosynthesis as a conserved pathway across all investigated Dasytinae symbionts, with additional amino acid and vitamin biosynthetic pathways being ancestrally encoded and retained in genomes of certain symbiont subclades but lost in others. These findings elucidate the function and dynamic evolutionary history of intracellular symbionts in pollen-feeding Dasytinae beetles and highlight the importance of tyrosine supplementation for the ecology and evolution across beetle families with diverse feeding ecologies.