The genome of a retreat-making caddisfly

The caddisfly Stenopsyche tienmushanensis Hwang was among the first described trichopterans by Chinese researchers. Sixty years after its scientific discovery to humans, the genome sequence of the species is now described for the first time, representing the best caddisfly genome by far. The new genome reveals potential linkage between genomic features (e.g., expansions of P450 and OBP families) and freshwater adaptations (e.g., tolerance to water pollutant, efficient mate finding during adult life stage). An exciting discovery of the new genome is the first description of the full-length H-fibroin gene, which codes for the major protein component of the caddisfly silk, a key adaptation trait to aquatic life.

Luo, S., M. Tang, P. B. Frandsen, R. J. Stewart, and X. Zhou*. 2018. The genome of an underwater architect, the caddisfly Stenopsyche tienmushanensis Hwang (Insecta: Trichoptera). GigaScience. Advanced online. doi:10.1093/gigascience/giy143. PDF

Abstract

Background

Caddisflies (Insecta: Trichoptera) are a highly adapted freshwater group of insects split from a common ancestor with Lepidoptera. They are the most diverse (> 16,000 species) of the strictly aquatic insect orders and are widely employed as bio-indicators in water quality assessment and monitoring. Among the numerous adaptations to aquatic habitats, caddisfly larvae use silk and materials from the environment (stones, sticks, leaf matter and etc.) to build composite structures such as fixed retreats and portable cases. Understanding how caddisflies have adapted to aquatic habitats will help explain the evolution and subsequent diversification of the group

Findings

We sequenced a retreat-builder caddisfly Stenopsyche tienmushanensis Hwang and assembled a high-quality genome from both Illumina and PacBio sequencing. In total, 601.2 M Illumina reads (90.2 Gb), and 16.9 M PacBio subreads (89.0 Gb) were generated. The 451.5 Mb assembled genome has a contig N50 of 1.29 M, a longest contig of 4.76 Mb, and covers 97.65% of the 1,658 insect single-copy genes as assessed by Benchmarking Universal Single-Copy Orthologs (BUSCO). The genome comprises 36.76% repetitive elements. A total of 14,672 predicted protein-coding genes were identified. The genome revealed gene expansions in specific groups of the cytochrome P450 family and olfactory binding proteins, suggesting potential genomic features associated with pollutant tolerance and mate finding. In addition, the complete gene complex of the highly repetitive H-fibroin, the major protein component of caddisfly larval silk, was assembled

Conclusions

We report the draft genome of Stenopsyche tienmushanensis, the highest quality caddisfly genome so far. The genome information will be an important resource for the study of caddisflies, and may shed light on the evolution of aquatic insects