PHYSIOLOGICAL ANALYSES OF HOST-FINDING BEHAVIOR IN TREMATODE CERCARIAE - ADAPTATIONS FOR TRANSMISSION SUCCESS

Physiological analyses of the behaviour of several cercarial species w hich actively find and invade their hosts have revealed very complex s equences of behaviour patterns and responses to very different stimuli from the environment and the host. A result of these physiological st udies is that the behaviour patterns of each of the species investigat ed are surprisingly individual. The behavioural patterns of host-findi ng of those species analysed in some detail reveal profound adaptation s to maximize transmission success. This can be demonstrated for movem ent patterns during swimming, for responses to environmental condition s such as gravity, light and temperature, for responses to stimuli ema nating from the host such as shadows, water turbulence and chemical co mpounds and especially for the responses after contact with the host. The behaviour patterns can be interpreted as adaptations to: (1) dispe rsal by leaving the habitat of the snail intermediate host and distrib ution within the area; (2) long survival by energy saving swimming beh aviour, by avoiding responses to inappropriate stimuli, by selecting f avourable microhabitats and probably by avoiding predation; (3) findin g and invading particular host types by selecting microhabitat's frequ ented by the hosts and responding to sequences of specific stimuli ema nating from the hosts.