Spiders (Araneae) have a diverse spectrum of morphologies, behaviours and physiologies. Initial attempts to understand the genomic-basis of this diversity are hindered by their large, heterozygous and AT-rich genomes with high repeat content resulting in highly fragmented, poor-quality assemblies. As a result, spider genomes’ key attributes, including gene family evolution, repeat content, and gene function, remain poorly understood. Here, we used Illumina and Dovetail Chicago technologies to sequence the genome of the long jawed spider Tetragnatha kauaiensis, producing an  assembly distributed along 3,925 scaffolds with a N50 of ~2 Mb. Using comparative genomics tools together with other available spider genomes, we explore genome evolution across available spider assemblies. Our findings suggest that genome size variation in spiders is linked to the different representation and number of transposable elements. Using statistical tools to uncover gene-family level evolution, we find expansions associated with the sensory perception of taste, immunity and metabolism. In addition, we report strikingly different histories of chemosensory, venom and silk gene families, with the first two evolving much earlier,  affected by the ancestral whole genome duplication in Arachnopulmonata  (~450 million years ago) and exhibiting higher numbers. Silk genes, on the other hand, are represented in lower numbers, but have a history of putative recent duplications. Together, our findings reveal that spider genomes are highly variable and that genomic novelty may have been driven by the burst of an ancient whole genome duplication, followed by gene family and transposable element expansion.

See Cerca et al 2022.