Sexual dimorphism in venom gland morphology in a sexually stinging scorpion

摘要

Males of several scorpion species possess bigger telsons than females. In at least some of these species, males repeatedly sting females during mating. This behaviour ('sexual sting') is likely correlated with a sexual dimorphism in telson and venom gland size. In sync with natural selection theory, females possess bigger venom glands because females need more nutrients for their offspring. Hence, we hypothesize that this sexual dimorphism in venom gland size evolved under sexual selection. We investigated the morphometrics and morphology of male and female telsons and venom glands of the sexually stinging scorpion Euscorpius alpha Caporiacco, 1950 (Euscorpiidae), using light and transmission electron microscopy. Male telsons are significantly bigger and more voluminous than those of females. Varying considerably between sexes, four different kinds of secretory cells are clearly distinguishable.The female secretory epithelium consists mainly of granule-filled cells while that of the males mainly has cells containing dissolvable vesicles. This cell type probably produces transparent venom that has been identified in other scorpions as so-called 'prevenom'. The role this "pre-venom" plays in sexual sting behaviour is addressed.