Generalist and specialist strategies in macrochelid mites (Acari: Mesostigmata) phoretically associated with dung beetles (Coleoptera: Scarabaeidae)

Abstract

Macrochelid mites have phoretic associations with coprophilous arthropods, thereby promoting dispersal and colonization of new substrates. Contrasting strategies were observed. Opportunistic mites like Macrocheles perglaber exploit a large range of carriers, whereas specialists like M. saceri occur only on roller dung beetles (genus Scarabaeus). The opportunistic species live inside dung pats, whereas specialists live in the pedotrophic nests of Scarabaeus beetles. These modes of life are expected to have consequences for host choice. We performed olfactometer tests and morphology comparisons to assess the adaptations of opportunists and specialists to their carrier hosts. The opportunist M. perglaber was shown to discriminate between various qualities of dung. Opportunists are thought to use this ability when their carrier buries a new dung pat and they have to decide whether to leave their carrier to live in a good-quality dung pat or to stay until the carrier finds another dung pat of good quality. The specialist M. saceri did not discriminate between qualities of dung; specialists always stay on the body of their host, whatever the dung quality. These life-style features are thought to describe essential differences between generalist and specialist macrochelids. Also morphometric parameters differed among three specialist and three generalist species. Relative to the generalists, specialists had a larger body and longer PI legs (= first leg pair); both characters are hypothesized to be an advantage in active searching for carrier hosts. Availability of carrier hosts is more likely limiting to specialists than to generalists. Small size has the advantage of reaching more prey living inside the dense dung material