Fig. 5

Hypotheses regarding the evolutionary derivation of spider venom glands. a Salivary gland origin hypothesis. We challenge this hypothesis based on the comparison results of module preservation, GO semantic similarity, and DUG similarity analyses (see Fig. 2). b Ancestral silk gland origin hypothesis. Our analyses prefer to support the concept that venom glands are likely derived from silk-producing glands present in early chelicerates. Previous assumptions were that spider silk glands evolved from accessory glands or were derived from the coxal glands [37, 38]. Modern spider silk glands may generate functional convergence with ancestral silk-producing glands, in turn resulting in high transcriptional similarities between spider venom glands and silk glands