Comparison of the gene expression patterns between the spider venom glands and other tissues

The evolution of venom has long fascinated biologists, especially the complex venom systems that have evolved independently in more than 100 metazoan lineages to facilitate prey capture and defense. The origin and evolution of these functionally novel organs remain poorly understood. Previous reviews highlighted that the spider venom system is derived from salivary glands or evolved from the silk-producing glands present in early chelicerates. To test two alternative hypotheses, we integrated the genomes and RNA-seq datasets from various lineages of spiders, scorpions, ticks, mites, centipedes and insects.