THE TEMPERATURE THRESHOLD FOR DEVELOPMENT OF ELAPHOSTRONGYLUS-RANGIFERI IN THE INTERMEDIATE HOST - AN ADAPTATION TO WINTER SURVIVAL

To test the hypothesis that the relatively high developmental temperat ure threshold of the parasitic nematode Elaphostrongylus rangiferi in the intermediate snail host is an adaptation to minimize larval mortal ity during winter, an experiment was set up in which snails of the spe cies Arianta arbustorum were experimentally infected with the parasite . The snails were divided into 3 groups known to contain Ist, 2nd or 3 rd-stage larvae, and incubated at 3 degrees C for an experimental peri od of 18 weeks. First-stage larvae showed a significantly higher survi val rate within snails than 2nd or 3rd-stage larvae. We also found tha t snails carrying 1st-stage larvae survived better than snails with ot her larval stages. It is concluded that if the nematode has started de velopment before the hibernation, this has a real and significant effe ct on the risk of dying. The high developmental threshold is therefore likely to be an adaptation to reduce the chance of hibernating as dev eloping larvae during long periods of low temperatures.