Biochemical Modulation of Venom by Spiders is Achieved Via Compartmentalized Toxin Production and Storage

Abstract

Animal venoms are complex chemical arsenals containing hundreds or even thousands of diverse small molecules, peptides, and proteins that affect a myriad of molecular targets. Because this biochemical arsenal is metabolically expensive, venom must be used sparingly and therefore one might predict that venom evolution would result in retention of only the most essential toxins for predation and/or defence. However, this presents a strong dichotomy in the functional requirements of venoms that are used for both predation and defence, which results in extensive functional redundancy. Here we show that spiders can overcome this potential metabolic burden by modulating the biochemical composition of their venom. We demonstrate that the venom peptidome of the lethal Australian funnel-web spider Hadronyche infensa changes both qualitatively and quantitatively throughout a series of defensive secretions — secretion of the most potent insecticidal toxins is preceded by secretion of non-insecticidal, presumably defensive, toxins. Using mass spectrometry imaging, we show that modulation of toxin secretion is facilitated by differential storage of toxins in the venom gland. We propose that the establishment of distinct venom-gland zipcodes for toxin production is an adaptation that reduces the metabolic expense of venom production and perhaps also serves to minimize effects from development of toxin resistance during predator-prey co-evolution. Our results highlight the importance of considering behavioral aspects of natural venom secretions in understanding toxin function and evolution.