Genomics of Caddisfly (Insecta: Trichoptera) Species Associated With Terrestrial Habitats

Limnephilidae is a species-rich and ecologically diverse family within the tube case making clade of caddisflies (Trichoptera). Species occur across a wide range of habitats, from cold headwater streams to stagnant pools to terrestrial environments. Here, we sequenced, assembled, and annotated whole genomes from two species that are associated with terrestrial environments: Enoicyla pusilla (Burmeister, 1839), distributed in the West Palearctic, and Philocasca rivularis (Wiggins, 1968), distributed in the Nearctic. Comprising three species, Enoicyla is the only genus of Trichoptera in Europe that exhibits a completely terrestrial life-cycle. As one of four species of Philocasca, larvae of P. rivularis also exhibit terrestrial behavior during wet months, dispersing across the forest floor up to several meters away from the stream channel. In both species, we investigated genomic features, for example, genome size and dynamics of transposable elements across Limnephilidae. We also explored potential molecular adaptations of silk to terrestrial versus aquatic environments. Characterization of the major silk gene, h-fibroin, of both species, as well as elemental analysis of silk of Philocasca rivularis, did not reveal molecular differences compared with silk of aquatic caddisfly species, potentially owing to the humid environments that both species inhabit. The new genomes form key resources for future genomic research on insect evolution, particularly related to habitat diversification and aquatic-terrestrial transitions.