Host specificity among species of Haematoloechus (Digenea: Haematoloechidae)

Comparative, experimental examinations of the host specificites of five species of the frog lung fluke genus Haematoloechus Looss, 1899 were conducted. Patterns of molluscan host utilization were examined for Haematoloechus breviplexus Stafford, 1902, Haematoloechus complexus (Seely, 1906), Haematoloechus longiplexus Stafford, 1902, Haematoloechus medioplexus Stafford, 1902, and Haematoloechus varioplexus Stafford, 1902. Haematoloechus breviplexus infections did not develop in the three gastropod species exposed to this parasite. Gyraulus parvus was the only snail species susceptible to infection with H. longiplexus and H. varioplexus and, along with Promentus exacuous, also was a suitable host for H. medioplexus. Haematoloechus complexus parasitized three species of physid snails but was unable to establish in seven other gastropod species. Within the second intermediate arthropod host H. complexus was demonstrated to be a generalist, parasitizing representatives of four insect orders and four crustacean species. Haematoloechus medioplexus and H. varioplexus were shown to be second intermediate host specialists, with metacercariae developing only in dragonflies, and H. longiplexus was demonstrated to be intermediate in specificity, developing metacercariae in both dragonflies and damselflies. These patterns of host specificity were demonstrated to be the result of species-specific repertoires of cercarial behavior. Haematoloechus complexus and H. longiplexus are active host invaders, with the more limited host range of H. longiplexus being attributable to site-specific penetration behavior. Haematoloechus medioplexus and H. varioplexus cercariae are passive host invaders that must be drawn into the rectal gill of their dragonfly hosts. These differences in host specificity appear to influence parasite population structure within the definitive host. At the level of the definitive host Rana catesbeiana proved refractory to infection with H. complexus, a result corroborated by field evidence. Both Rana pipiens and Rana blairi were susceptible to infection with H. longiplexus, but this parasite was rarely found in these frogs from nature. The nature of host specificity varies within a species across life cycle stages. This is the result of the action of the different selective pressures that operate on different life cycle stages