Mite Genome Miniaturization: Assembly of the biological control agent Floracarus perrepae reveals dynamic genome evolution in eriophyoid mites

The eriophyoid mites (Acari: Eriophyoidea) represent an extreme case of genome streamlining, with genomes averaging just 32Mb, among the smallest of all animals. This clade of mites is highly diverse with more than 4000 species. Their morphologies are specialized for feeding on their host plants, including a simplified worm-like body plan with just two pairs of legs and modified mouth parts that can induce the formation of galls or plant deformities during feeding. Their generally strong host affinities make eriophyoid mites appealing for use as biological control agents, although their short generation times and small genomes could facilitate rapid evolution and impact their efficacy in management programs. Here, we sequenced the genome of the biological control mite Floracarus perrepae, producing a highly contiguous genome totalling just 23.1 Mb, among the smallest of all animals. We also assembled another non-eriophyid mite genome from accidental DNA bycatch (69.4Mb). We placed this new genomic resource in a phylogenetic context to reveal that mites have highly dynamic genome evolution, with a significant trend in genome downsizing in the eriophyoids. Our results suggest that this streamlining is associated with non-genic elements such as the suppression or excision of retrotransposons and purging of introns. As new sequencing techniques become available, novel genomic resources for tiny organisms such as F. perrepae will be more readily accessible, facilitating both fundamental genome evolutionary biology and applied sciences such as biological control programs which use eriophyoid mites for the management of invasive species.