Lifestyles shape genome size and gene content in fungal pathogens

Fungi have a wide range of lifestyles and hosts. We still know little about the impact of lifestyles on their genome architecture. Here, we combined and annotated 562 fungal genomes from the class Sordariomycetes and examined the coevolution between 12 genomic and two lifestyle traits: pathogenicity and insect association. We found that pathogens tend to evolve a larger number of protein-coding genes, tRNA genes, and have larger non-repetitive genome sizes than non-pathogenic species. In contrast, species with a pathogenic or symbiotic relationship with insects have smaller genome sizes and genes with longer exons; they also have fewer genes if they are vectored by insects, compared to species not associated with insects. Our study demonstrates that pathogen genome size and complexity are the result of an interplay between drift, imposed by symbiosis and small effective population size, which leads to genome contraction, and the adaptive role of gene amplification, which leads to genome expansion. ### Competing Interest Statement The authors have declared no competing interest.