Thermal preferences of wintering snails Planorbarius corneus (L.) exposed to lipopolysaccharide and zymosan.

Fever is regarded as a physiological response to infection both in endothermic and ectothermic animals. In ectotherms, fevers are achieved only behaviorally, and has been described in many vertebrates' and few invertebrates' groups. In snails only symptoms of reverse fever as a response to trematode invasion were found. Present work reports on the effects of two different pyrogens - lipopolysaccharide extracted from Escherichia coli (LPS), and zymosan - from Saccharomyces cerevisiae on the thermal behavior of wintering (studied during a winter season) specimens of the Planorbarius corneus (L.). Using the thermal gradient protocol we demonstrate that the individuals of this snail species responded with behavioral fevers to dosages of pyrogens. LPS injection to the surface of the snail's foot at a dose of 10 µg/g resulted in a significant increase in preferred temperature at 5h after injection. Similarly zymosan at a dose of 0.5 and 1.0 µg/g - caused fever at 8h and 9h respectively. Average temperature chosen by feverish animals after latency period reached 28.7±0.41 °C (LPS), 28.1±0.43 °C (zymosan 1.0 µg/g) or 25.5±0.33 °C (zymosan 0.5 µg/g). We conclude, therefore, that snails are capable of reacting with fever to selected pathogen associated factors, and P. corneus can be used as a model to study a behavioral fever phenomenon in invertebrate animals.