Tetragnatha kauaiensis genome

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.