Venom systems are complex traits that have independently emerged multiple times in diverse plant and animal phyla. Within each venomous lineage there typically exists interspecific variation in venom composition where several factors have been proposed as drivers of variation, including phylogeny and diet. Understanding these factors is of broad biological interest and has implications for the development of antivenom therapies and venom-based drug discovery. Because of their high species richness and the presence of several major evolutionary prey shifts, venomous marine cone snails (genus Conus) provide an ideal system to investigate drivers of interspecific venom variation. Here, by analyzing the venom gland expression profiles of ∼3,000 toxin genes from 42 species of cone snail, we elucidate the role of prey-specific selection pressures in shaping venom variation. By analyzing overall venom composition and individual toxin structures, we demonstrate that the shifts from vermivory to piscivory in Conus are complemented by distinct changes in venom composition independent of phylogeny. In vivo injections of venom from piscivorous cone snails in fish further showed a higher potency compared with venom of nonpiscivores demonstrating a selective advantage. Together, our findings provide compelling evidence for the role of prey shifts in directing the venom composition of cone snails and expand our understanding of the mechanisms of venom variation and diversification.

Mollusk-hunting (molluscivorous) cone snails belong to a monophyletic group in Conus, a genus of venomous marine snails. The molluscivorous lineage evolved from ancestral worm-hunting (vermivorous) snails ∼18 million years ago. To enable the shift to a molluscivorous lifestyle, molluscivorous cone snails must solve biological problems encountered when hunting other gastropods, namely: 1) preventing prey escape and 2) overcoming the formidable defense of the prey in the form of the molluscan shell, a problem unique to molluscivorous Conus. Here we show that χ-conotoxins, peptides exclusively expressed in the venoms of molluscivorous Conus, provide solutions to the above problems. Injecting χ-conotoxins into the gastropod mollusk Aplysia californica results in impaired locomotion and uncoordinated hyperactivity. Impaired locomotion impedes escape and a hyperactive snail will likely emerge from its shell, negating the protection the shell provides. Thus, χ-conotoxins are an evolutionary innovation that accompanied the emergence of molluscivory in Conus and provide solutions to problems posed by hunting other snails.

Peptide hormones and neuropeptides form a diverse class of bioactive secreted molecules that control essential processes in animals. Despite breakthroughs in peptide discovery, many signaling peptides remain undiscovered. Recently, we demonstrated the use of somatostatin-mimicking toxins from cone snails to identify the invertebrate ortholog of somatostatin. Here, we show that this toxin-based approach can be systematically applied to discover other unknown secretory peptides that are likely to have signaling function. Using large sequencing datasets, we searched for homologies between cone snail toxins and secreted proteins from the snails’ prey. We identified and confirmed expression of five toxin families that share strong similarities with unknown secretory peptides from mollusks and annelids and in one case also from ecdysozoans. Based on several lines of evidence we propose that these peptides likely act as signaling peptides that serve important physiological functions. Indeed, we confirmed that one of the identified peptides belongs to the family of crustacean hyperglycemic hormone, a peptide not previously observed in Spiralia. We propose that this discovery pipeline can be broadly applied to other systems in which one organism has evolved molecules to manipulate the physiology of another.

Organisms engage in chemical interactions that drive cooperation, conflict, natural selection, and adaptation. Among these, doppelgänger peptides (molecular mimics of the endogenous hormones or neuropeptides of another organism) have evolved in many venomous and poisonous organisms, and some parasites and pathogens. While the discovery of these peptides has been largely anecdotal, a surge in sequence data combined with computational tools suggests they are more prevalent than previously recognized. Beyond their significance in biology, emerging techniques for studying cellular signaling and a renewed interest in peptide-based therapeutics position these molecules as candidates for translational applications. In this review, we explore the role of doppelgänger peptides in chemical ecology, molecular evolution, and medicine, and provide new perspectives to guide future research.

Natural selection can drive the evolution of similar traits through convergent evolution. Short peptides identical to the vertebrate hormone bradykinin (BK) have been reported from the venoms and skin secretions of certain species of wasps (order Hymenoptera) and frogs (order Anura), respectively. In this study, we demonstrate that the genes encoding the BK-like peptides of hymenopteran venoms and anuran skin secretions do not share common ancestry with that of the vertebrate hormone but instead independently evolved multiple times from peptide toxin genes. These peptides serve a defensive function against vertebrate predators and their resemblance to BK was driven by selection for efficacy at the predators’ receptors. Our findings highlight how natural selection can drive repeated convergent evolution of similar molecules across distantly related lineages.

Persistent pain affects one in five people worldwide, often with severely debilitating consequences. Current treatment options, which can be effective for mild or acute pain, are ill-suited for moderate-to-severe persistent pain, resulting in an urgent need for new therapeutics. In recent years, the somatostatin receptor 4 (SSTR ₄ ), which is expressed in sensory neurons of the peripheral nervous system, has emerged as a promising target for pain relief. However, the presence of several closely related receptors with similar ligand-binding surfaces complicates the design of receptor-specific agonists. In this study, we report the discovery of a potent and selective SSTR ₄ peptide, consomatin Fj1, derived from extensive venom gene datasets from marine cone snails. Consomatin Fj1 is a mimetic of the endogenous hormone somatostatin and contains a minimized binding motif that provides stability and drives peptide selectivity. Peripheral administration of synthetic consomatin Fj1 provided analgesia in mouse models of postoperative and neuropathic pain. Using structure-activity studies, we designed and functionally evaluated several Fj1 analogs, resulting in compounds with improved potency and selectivity. Our findings present a novel avenue for addressing persistent pain through the design of venom-inspired SSTR ₄ -selective pain therapeutics. One Sentence Summary: Venom peptides from predatory marine mollusks provide new leads for treating peripheral pain conditions through a non-opioid target.