Meeting Abstract
A goal of venom evolution studies is to identify the causes and consequences of intra- and interspecific variation in venom. Determining the effects of drift and selection is complicated by the difficulty linking phenotype with genotype. While selection is often demonstrated through geographic patterns in venom toxicity and target resistance, identifying the molecular changes that regulate toxicity may be problematic because many venoms have complex compositions. Scorpions in the genus Centruroides are ideal for investigating venom diversity; the venoms exhibit intra- and interspecific variation in lethality and pain-inducing capability, and because both the toxins (proteins) and their targets (sodium and potassium ion channels in nerve and muscle) are encoded by genes, changes in venom toxicity and target resistance can be linked to molecular changes. In the Sonoran desert, Onychomys torridus (grasshopper mice) prey on C. sculpturatus. Mice are resistant to venom pain via molecular changes to a sodium channel that enables the channel to bind a venom protein and block the pain signal the venom is initiating. Thus, the mice have adapted to the defenses of their prey. If reciprocal selection is driving this system, scorpions may have responded by expressing less of the protein that blocks pain signals in the mice, or via changes in the protein’s structure so it no longer binds the mouse’s channel. We compared venom proteins and ion-channel genes from Sonoran desert species to orthologs from Chihuahuan desert species (C. vittatus, O. arenicola) that differ in painfulness and resistance, respectively. While sodium channel genes did not differ between O. torridus and O. arenicola, C. vittatus appear to have lost the venom protein that blocks pain in grasshopper mice, suggesting that C. vittatus have “countered back”.
