Meeting Abstract

S2.10  Sunday, Jan. 4  Life history of gnathiid isopods: a brief overview TANAKA, K.; Japan Agency for Marine-Earth Science and Technology katsuhikot@jamstec.go.jp

Gnathiidae is a family of the order Isopoda including over 180 species worldwide. The larvae are known as common ectoparasites of fishes, particularly in coral reef regions. Adult gnathiids however are morphologically very different from the larvae, show strong sexual dimorphism and are regarded to be non-feeding. The biphasic life cycle of gnathiids including a fish-parasitic larval phase and non-feeding adult phase may be an evolutionary product of inter- and intra-specific interactions which gnathiids and their ancestors have experienced and a good example for considering the diversity and adaptation of parasitic crustaceans. Although our current understanding on the life cycle of gnathiids is still based on information on a limited number of species and/or fragmented descriptions, some general features can be deduced as follows: 1) larval gnathiids are temporary ectoparasites and develop into adults after alternating several times (three times in many cases) between ectoparasitic events and host-independent molting; 2) larvae stay on fish hosts for only a short period (minutes to hours on teleosts) during each ectoparasitic event and then 3) rest and molt in benthic habitats (e.g. mud burrows, sponges) between subsequent ectoparasitic events; 4) adults reproduce in benthic habitats, identical to larval benthic habitat in some species and different in others, and sometimes form harem-like aggregations. Several isopod families such as Cymothoidae are also known as ectoparasites of fishes but the repetition of short ectoparasitic events and the high dependency on benthic habitats are less remarkable in those taxa than in Gnathiidae. I will briefly review the life history of gnathiids, employing the data on two Japanese species, and discuss the possible factors, such as predation, affecting their specialization.