Meeting Abstract
Pain, though unpleasant, is adaptive in calling an animal’s attention to potential tissue damage. Many animals have evolved specialized sensory structures, including mammalian nociceptors, for detecting and responding to noxious stimuli. Animals representing diverse taxa (platypuses to snakes to scorpions) possess venom-mediated, pain-inducing bites or stings that activate the pain-sensing pathways of potential enemies (predators, competitors). While the fitness benefits of possessing a painful sting seem obvious to anyone who has been stung by a wasp, few studies have demonstrated such benefits. Southern grasshopper mice are voracious predators of scorpions. The mice consume a diversity of species, including intensely painful Arizona (AZ) bark scorpions and nearly painless stripe-tailed scorpions. AZ bark scorpion venom induces pain by activating Nav1.7, the sodium channel that initiates pain signals in sensory neurons. Southern grasshopper mice reduce their sensitivity to venom pain via molecular modifications to a second channel, Nav1.8, which blocks transmission of pain signals to the brain. However, mice are not completely resistant to pain, they respond to stings by grooming briefly. We asked if brief pain influences prey choice. Results from laboratory experiments demonstrate that painful stings do 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. Foraging choices were also mediated by the mice’s condition; lean wild-caught mice preferred stripe-tailed scorpions to bark scorpions, but readily consumed both. Captive-born, well-nourished mice with unrestricted access to mouse chow, in contrast, often chose to stop feeding on scorpions altogether.
