A highly lethal class of toxins from the venom of Australian funnel web spiders likely developed as a predator defense, and the toxin's lethality to humans was an evolutionary coincidence, a study suggests. While 35 species of Australian funnel-web spiders have been described, the diversity of the spiders' δ-hexatoxins remains underexplored, with only nine δ-hexatoxins from four species previously characterized. Bryan G. Fry, Volker Herzig, Glenn F. King, and colleagues profiled transcriptomes, or gene expression signatures, from 10 funnel web spider species and identified 22 additional δ-hexatoxins. Most human envenomations occur when male spiders wander from their burrows during the spiders' mating season and when the male spiders are unlikely to feed, suggesting that the venom plays a defensive role. Genetic analysis revealed highly conserved sequences among the δ-hexatoxins, consistent with a role in defense against predators. Additionally, one δ-hexatoxin, δ-HXTX-Ar1a, inhibited inactivation of voltage-gated sodium channels in cockroaches and was toxic to sheep blowflies. The same inactivation inhibition pathway also induced pain in mice. According to the authors, the toxins likely developed from an insecticidal predatory function into a defense mechanism against nonhuman vertebrate predators, with the high human toxicity emerging as an evolutionary coincidence.
Article #20-04516: "Australian funnel-web spiders evolved human-lethal δ-hexatoxins for defense against vertebrate predators ," by Volker Herzig, Kartik Sunagarc, David T. R. Wilsond, Sandy S. Pineda et al.
MEDIA CONTACT: Bryan G. Fry, University of Queensland, Brisbane, AUSTRALIA; e-mail: bgfry@uq.edu.au
###
Proceedings of the National Academy of Sciences