To molt or not to molt: The dilemma of acquiring sexual maturity while losing durability and dispersal ability in deutonymphs of Parasitus fimetorum (Gamasida; Parasitidae)

Abstract

Abstract The dispersal from birthplace is an effective strategy to cope with unpredictable environmental change. In many animals, dispersal is carried out prior to mating and reproduction to avoid inbreeding. However, this also means that the dispersers have to find mate at the new habitat. Parasitus fimetorum (Acari; Parasitidae) is a free-living predatory mite inhabiting animal dung and manures. In such ephemeral habitats, the mites quickly develop from eggs to deutonymphs as an environmentally-tolerant, dispersal stage. After the dispersal to new habitat using dung beetles as phoretic hosts, deutonymphs have to make a decision; to molt to adult with losing the tolerance and migration ability or not to molt and continue migration. Here, using the molting-suppressed deutonymphs which were developed under isolated condition, I investigated whether food conditions (amount of rearing medium bearing nematodes as prey) and the encounter with conspecifics stimulate their molting. Drastic increase of the food resources induced molting of both sexes but the responses to the pairing treatment were different between sexes. Whereas female deutonymphs molted at the encounter with males irrespective of deutonymphs or adults, molting of male deutonymphs was induced only when paired with female deutonymphs (not adult females). Because the adult females are usually non-virgin and already started oviposition, the males seemed to discriminate against them. The decision about molting is understandable as a male mate choice, which is adaptive at the limited mating opportunities in the ephemeral environments.