Meeting Abstract

S8.10  Thursday, Jan. 6  Hatching strategies in parasitic monogeneans (platyhelminths) that facilitate host infection WHITTINGTON, I.D.*; KEARN, G.C.; South Australian Museum/University of Adelaide, Australia; University of East Anglia, Norwich, UK ian.whittington@samuseum.sa.gov.au

In parasites, environmental cues have great potential to influence egg hatching and enhance infection success. Monogeneans are parasitic platyhelminths that are among the most host specific of all parasites. Most monogeneans are ectoparasites with direct life cycles tied to water. They infect a single host species, usually a fish, although some are endoparasites of amphibians and aquatic chelonian reptiles. The two other major groups of parasitic platyhelminths, the cestodes (tapeworms) and digeneans (flukes) are endoparasites, infect more than one host species and employ trophic transmission. The eggs of monogeneans have strong shells and mostly release ciliated larvae, which, against all odds, must find, identify and infect a suitable specific host. Some monogeneans spread the risk of finding a new host by greatly extending the hatching period (possible bet-hedging). Other monogeneans respond to hatching cues such as shadows, mechanical disturbance, chemicals and osmotic changes, most of which are generated by the host. Hatching may be rhythmical, larvae emerging at times when the host is most vulnerable to invasion, and this may be combined with responses to other environmental cues. Different monogenean species that infect the same host species may adopt different hatching strategies, indicating that tactics may be more complex than first thought. Some monogeneans enhance host infection by attaching eggs to the host or by retaining eggs on or inside the body of the parasite. The latter may lead ultimately to viviparity, as, for example, in gyrodactylid monogeneans.