CLAUSSEN, D.L.*; GRISAK, A.G.; BROWN, P.F.; Miami Univ., Oxford, OH; Case Western Reserve Univ., Cleveland, OH; Georgia Southwestern State Univ., Americus: The thermal relations of the freshwater triclad flatworm, Dugesia dorotocephala (Turbellaria: Tricladida)

Although Dugesia dorotocephala is among the most widely distributed and eurythermal triclads within North America, its thermal relations are poorly known. We compared the upper thermal tolerances of planarians acclimated to 15 or 22 °C and the temperatures they selected within a circular gradient. We also compared speeds of planarians tested at 22 °C after up to 10 days of starvation or after acclimation to 15, 22, or 30 °C. We further compared speeds of 22 °C acclimated animals at temperatures from 10 to 30 °C, and we examined the interaction between temperature and water viscosity. The triclads survived temperatures close to 33 °C for up to 12 hr, but had incipient lethal temperatures around 30.5 °C. Warm acclimated animals survived somewhat better at the higher, but not at the lower, test temperatures. The triclads selected temperatures between 12 and 28 °C, with the 15 °C acclimated animals selecting higher mean temperatures than the 22 °C acclimated animals. The latter group showed a normally distributed selection pattern, whereas that of the former group was skewed to the right. Speeds increased during the first two days of fasting but showed no further changes between days 3 and 10. Speeds increased with body size with a scaling exponent of about 0.25. There was a significant effect of temperature, with a Q₁₀ of 2.31 between 10 and 30 °C. Thermal acclimation had a significant effect on locomotion, with 30 °C acclimated animals being markedly slower than 15 or 22 °C acclimated invidivuals. Although there was some indication of a viscosity effect, the results were not statistically significant.