Altered behaviour leading to selective predation of amphipods infected with acanthocephalans, with special reference to Polymorphus paradoxus / William M. Bethel

The freshwater amphipods, Gammarus lacustris and Hyalella azteca,infected with acanthocephalan and cestode larvae were used to test Holmes and Bethel's (in press) hypothesis that some parasites have adopted the evolutionary strategy of altering the bahaviour of their intermediate hosts so as to increase the vulnerability of the latter to predation by the definitive host. Uninfected G. lacustris and H. azteca are strongly photophobic, negatively phototactic, and found in the bottom ooze and heavily vegetated areas of the lakes. They evade disturbance by diving to the bottom, often burrowing into the sediment or crawling under debris; the primary directive for this response is their negative phototaxis. The behaviour and distribution of gammarids infected with cystacanths of Polymorphus contortus (Acanthocephala:Polymorphidae) and the cysticercoids of Lateriporus mathevossianae, L.skryabini, and L. clerci (Cestoda: Dilepidae) were indistringuishable from those of the uninfected amphi