TOXIN EVOLUTION IN SCORPION VENOM: EVIDENCE FOR TOXIN DIVERGENCE UNDER STRONG NEGATIVE SELECTION IN LEIURUS QUINQUESTRIATUS SUBSPECIES

The Buthid scorpion Leiurus quinquestriatus is divided into two sub-species whose region of contact occurs at the Suez Isthmus. L.q. quinquestriatus, found in the North Africa is distinguished from L.q. hebraeus by minor differences in morphology. Despite the very high similarity in body plan, out of the 24 toxins isolated from this species none is common to both sub-species, suggesting a degree of molecular divergence not apparent at the morphological level. We show, by comparison with two sets of reference proteins from humans and Old-World monkeys, that divergence of toxins with common structures and functions in these two sub-species has occurred under conditions of strong negative selection. Potential selection pressures responsible for toxin divergence are discussed, including the role of conflicting interests during courtship.