Weapon polymorphism in arthropods: novel cases of multiple weapon morphs within single species (#444)
Animal weapons are typically possessed by males that use these exaggerated traits to fight with other male competitors and increase reproductive success. The expression of weaponry is often highly variable among individuals, and in many species morphs are divided between large (armed) and small (unarmed) males in accordance with one or more developmental thresholds. These thresholds that divide males into discrete morphs are condition-dependent and strongly associated with body size, such that small-bodied males typically lack big weapons and rely on alternative behavioural tactics to gain access to females for copulation. Recently we conducted a behavioural and morphometric study of Pantopsalis cheliferoides , a harvestmen (Arachnida: Opiliones) from New Zealand. Male P. cheliferoides possess extremely exaggerated chelicerae which are highly variable in length among individuals. Across the same body size spectrum, however, some males belong to a distinct second exaggerated morph which possesses short, broad chelicerae, which were also found to be used as weapons. Remarkably, we discovered a similar pattern in an unrelated brentine weevil (Cephalobarus macrocephalus; Coleoptera: Brentidae) highlighting the possibility that multiple weapons forms in other animals may be prevalent. We will address the implications of these findings, especially with regards to our understanding of the evolution and maintenance of developmental thresholds and weapon polymorphism.