The extraordinary mating system of Zeus bugs (Heteroptera:Veliidae:Phoreticovelia sp.)

Abstract

Wingless female Zeus bugs (genus: Phoreticovelia) produce a secretion from dorsal glands that males feed upon when riding on females. This unique form of sex-role-reversed nuptial feeding may have set the stage for an unusual mating system. Here, we provide natural history details of the mating behaviour for two Zeus bug species. While these species have many mating behaviours in common, the wing morphs within species exhibit entirely different mating strategies. Adult wingless females are ridden permanently by adult wingless males. In the wild, adult sex-ratios among the wingless morph are male-biased; few unmounted adult females exist and many males instead ride immature females who also produce glandular secretions. In contrast, sex-ratios among the winged morph is not male-biased, sexual size dimorphism is less pronounced, females have no dorsal glands and are, consequently, not ridden by males. Field and laboratory observations show that mating is strongly assortative by wing morph. This assortment may allow evolutionary divergence between the two morphs. We discuss the implications of this mating system and suggest that it adds to those studies showing that sexually antagonistic coevolution can be a driver of mating system evolution.