Genomics and CT imaging reveal diversity in silk genes and gland morphology of webspinners

Webspinners (Insecta: Embioptera) are an unusual insect order that are known for their subsocial behavior and prolific silk-production. Due to their unique foreleg silk glands, and spider-like ability to produce silk throughout their entire life cycle, webspinners are hypothesized to have evolved silk independently from other arthropod lineages. To date, there are no high-quality contig-level genome assemblies available for the order, preventing the study of their silk gene origination and diversification. Here, we assembled PacBio HiFi contig-level genomes and characterized the silk genes present in two webspinner species, Aposthonia ceylonica and Oligotoma nigra. The genomes reveal multiple full-length copies of the primary Embioptera silk gene, e-fibroin, that have undergone both ancestral and recent gene duplications within the group. For both species, all e-fibroin paralogs show the presence of complex repeat units consisting of multiple exons and introns that are remarkably homogenized across each gene. We also used µCT-scanning of the internal silk glands to provide details concerning the localization of silk production in foreleg tarsi, and interspecific morphology.