Diverse and complex male polymorphisms in Odontolabis stag beetles (Coleoptera: Lucanidae)

When male animals engage in intrasexual contests then any alternative tactics they use can be associated with dimorphisms in the expression of weapons. Some species have recently been found to exhibit trimorphism in their weaponry, suggesting that the processes leading to their evolution and maintenance of these polymorphisms can be more complex than previously thought. Here, we describe the extraordinary diversity of polymorphism within the genus Odontolabis: there are dimorphic species (O. siva and O. platynota), trimorphic species (O. cuvera, as previously described, and O. sommeri s.stricto) and, uniquely, tetramorphic species, with males of O. sommeri lowei and O. brookeana showing four clearly differentiated male morphs: small “Gammas”, “Alphas” which express large, long mandibles, “Betas” which have long mandibles with different morphology and “Boltcutters”, with short, wide mandibles. Such polymorphisms are usually thought of as being maintained as a status-dependent conditional strategy, but we found only one size threshold: in most cases males develop into Gamma males below a certain size but there is no relationship between morph and body size amongst the larger, ‘weaponised’ morphs. We suggest that the complex polymorphisms in these animals are probably maintained by a combination of a conditional strategy and a genetic polymorphism.