Defensive Venoms: Is Pain Sufficient for Predator Deterrence?

Abstract

Pain, though unpleasant, is adaptive in calling an animal’s attention to potential tissue damage. A long list of animals representing diverse taxa possess venom-mediated, pain-inducing bites or stings that work by co-opting the pain-sensing pathways of potential enemies. Typically, such venoms include toxins that cause tissue damage or disrupt neuronal activity, rendering painful stings honest indicators of harm. But could pain alone be sufficient for deterring a hungry predator? Some venomologists have argued “no”; predators, in the absence of injury, would “see through” the bluff of a painful but otherwise benign sting or bite. Because most algogenic venoms are also toxic (although not vice versa), it has been difficult to disentangle the relative contributions of each component to predator deterrence. Southern grasshopper mice (Onychomys torridus) are voracious predators of arthropods, feeding on a diversity of scorpion species whose stings vary in painfulness, including painful Arizona bark scorpions (Centruroides sculpturatus) and essentially painless stripe-tailed scorpions (Paravaejovis spinigerus). Moreover, southern grasshopper mice have evolved resistance to the lethal toxins in bark scorpion venom, rendering a sting from these scorpions painful but harmless. Results from a series of laboratory experiments demonstrate that painful stings matter. Grasshopper mice preferred to prey on stripe-tailed scorpions rather than bark scorpions when both species could sting; the preference disappeared when each species had their stingers blocked. A painful sting therefore appears necessary for a scorpion to deter a hungry grasshopper mouse, but it may not always be sufficient: after first attacking and consuming a painless stripe-tailed scorpion, many grasshopper mice went on to attack, kill, and eat a bark scorpion even when the scorpion was capable of stinging. Defensive venoms that result in tissue damage or neurological dysfunction may, thus, be required to condition greater aversion than venoms causing pain alone.

Transcriptomic Analysis of Four Cerianthid (Cnidaria, Ceriantharia) Venoms

“…For instance, if Ceriantharia is sister to the Hexacorallia, that suggests that the expansion of neuropeptide toxins occurred after the divergence of Ceriantharia, possibly through extensive gene duplications [ 52 , 130 , 135 ]. Neurotoxins in sea anemones are important because they are sessile animals, and may be critical to deterring predators [ 136 ]. Because cerianthids can fully contract into their tubes, they have a distinct means of protecting themselves from predators in contrast to sea anemones which cannot fully retract their bodies, which may ease the selective pressure to diversify or maintain defensive toxins.…”

Transcriptomic analysis of four cerianthid (Cnidaria, Ceriantharia) venoms

“…Ceriantharia is sister to the Hexacorallia, that suggests that the expansion of neuropeptide toxins occurred after the divergence of Ceriantharia, possibly through extensive gene duplications [52,126,131]. Neurotoxins in sea anemones are important because they are sessile animals, and may be critical to deterring predators [132]. protein [135], which can be an important mechanism of prey capture at night [136].…”

Phylogenomics of scorpions reveal a co-diversification of scorpion mammalian predators and mammal-specific sodium channel toxins

“…All scorpions are thought to possess insect-specific ion channel toxins, which facilitate prey capture. Within buthids, salient components of the venom cocktail are ion channel toxins that are specific to mammalian targets and are inferred to function as anti-predator deterrents (Niermann et al 2020). Such neurotoxins operate by blocking action potentials at nerve synapses, precipitating symptoms of neurotoxicosis such as intense pain, hypersalivation, muscle spasms, asphyxia, and paralysis.…”