Changes in predator exposure, but not in diet, induce phenotypic plasticity in scorpion venom

Abstract

Animals embedded between trophic levels must simultaneously balance pressures to deter predators and acquire resources. Venomous animals may use venom toxins to mediate both pressures, and thus changes in this balance may alter the composition of venoms. Basic theory suggests that greater exposure to a predator should induce a larger proportion of defensive venom components relative to offensive venom components, while increases in arms races with prey will elicit the reverse. Alternatively, reducing the need for venom expenditure for food acquisition, for example because of an increase in scavenging, may reduce the production of offensive venom components. Here, we investigated changes in scorpion venom composition using a mesocosm experiment where we manipulated scorpions' exposure to a surrogate vertebrate predator and live and dead prey. After six weeks, scorpions exposed to surrogate predators exhibited significantly different venom chemistry compared with naive scorpions. This change included a relative increase in some compounds toxic to vertebrate cells and a relative decrease in some compounds effective against their invertebrate prey. Our findings provide, to our knowledge, the first evidence for adaptive plasticity in venom composition. These changes in venom composition may increase the stability of food webs involving venomous animals.

Reciprocal transplantation of the heterotrophic coral Tubastraea coccinea (Scleractinia: Dendrophylliidae) between distinct habitats did not alter its venom toxin composition

“…Venomous anthozoans often elaborate the same combination and potency of toxins for both predation and defense, potentially where constitutive expression is adequate for both purposes, even during a severe “bleaching” event causing an enhance requirement for heterotrophic metabolism (Hoepner, Abbott, & Burke da Silva, ). Changes in predator exposure, but not diet, elicit a larger venom proportion of defensive toxins than predatory toxins in the scorpion Liocheles waigiensis (Gangur et al, ), and remarkably, carnivorous cone snails are reported to switch between distinct venoms in response to predatory or defensive stimuli (Duterte et al, ). The only known predators of T. coccinea in the tropical Indo‐Pacific are the gastropod Epidendrium billeeanum (Rodríguez‐Villalobos, Ayala‐Bocos, & Hernandez, ) and the nudibranch Phyllida melanobrachia (Okuda, Klein, Kinnel, Li, & Scheuer, ), while generalist predators are yet to be detected within invaded habitats of the southwestern Atlantic (Moreira & Creed, ).…”

Venom Costs and Optimization in Scorpions

“…Recent evidence suggests scorpions can modify their venom composition in response to predator exposure (Gangur et al, 2017). Repeated periodical encounters with a surrogate vertebrate predator (a taxidermied mouse) over a 6 week period led Hormurus waigiensis to appear to produce a higher relative abundance of some vertebrate specific toxins used in defensive situations, and a lower relative abundance of certain toxins specific to their invertebrate prey (Gangur et al, 2017). This study provided the first evidence for adaptive plasticity in venom compositions, and suggested it has evolved as a mechanism to allow for the optimization of venom use (Gangur et al, 2017).…”

“…Repeated periodical encounters with a surrogate vertebrate predator (a taxidermied mouse) over a 6 week period led Hormurus waigiensis to appear to produce a higher relative abundance of some vertebrate specific toxins used in defensive situations, and a lower relative abundance of certain toxins specific to their invertebrate prey (Gangur et al, 2017). This study provided the first evidence for adaptive plasticity in venom compositions, and suggested it has evolved as a mechanism to allow for the optimization of venom use (Gangur et al, 2017). Modification of venom composition in response to environmental pressures could allow scorpions to further optimize venom use in different environments.…”

“…Therefore, ability to plastically change venom composition can allow scorpions to prioritize their resources and minimize the costs of venom use. It is currently unclear what environmental cues (e.g., olfactory) led to the plastic response observed by Gangur et al (2017). Furthermore, it is unclear if the response was targeted specifically at the presence of the mouse, or if it was a uniform response to increased predation pressure.…”

“…Scorpions utilize venom to both capture prey and defend against predators, which can include organisms with very different physiologies and susceptibility to venom components (Gangur et al, 2017;van der Meijden et al, 2017). Over 400 million years of evolution (Dunlop and Selden, 2009) have led scorpions to develop a wide range of mechanisms that help minimize the costs of venom use.…”