Mite dilemma: molting to acquire sexual maturity or not molting to ensure durability and dispersal ability in Phorytocarpais fimetorum (Parasitiformes; Gamasida; Parasitidae)

Abstract

Dispersal from birthplace is an effective strategy to cope up 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 must find mates in the new habitat. Phorytocarpais fimetorum (= former name Parasitus fimetorum) is a free-living predatory mite inhabiting animal dung and manure. In such ephemeral habitats, the mites quickly develop from egg to deutonymph as the environmentally tolerant, dispersal stage via larva and protonymph stages. After dispersal to new habitats utilizing dung beetles as phoretic hosts, deutonymphs have to decide whether to molt to adulthood by losing their tolerance and migration ability or not to molt and continue dispersal. Here, using molt-suppressing deutonymphs that were obtained under isolated conditions, I investigated whether food conditions (amount of rearing medium bearing nematodes as prey) and encounters with conspecifics stimulate their molting. A drastic increase in food resources induced molting in both sexes, but the responses to the pairing treatment were different between sexes. Whereas female deutonymphs molted at the encounter with males regardless of whether they were deutonymphs or adults, molting of male deutonymphs was induced only at the pairing with female deutonymphs (not adult females). Because adult females are usually nonvirgin and have already started oviposition, the males seemed to discriminate against them. The decision about molting is understandable as a male mate choice, which is adaptive to the limited mating opportunities in ephemeral environments.