Thermal Tolerances of an Endemic Hot Spring Snail Physella wrighti Te and Clarke (Mollusca: Physidae)

Abstract

Physella wrighti (Te and Clarke, 1985) is an Endangered freshwater snail endemic to the Liard Hot Springs in northern British Columbia. It inhabits water temperatures from 23.5oC to 36oC and is active year-round. Despite its conservation status, little else is known about this species. To advance our understanding of P. wrighti in its environment, I investigated how water temperature affects aspects of its life history in a lab setting. I first investigated if P. wrighti would be more active in the scotophase versus the photophase at 30oC and observed no differences in activity level. I tested if P. wrighti had a preferred water temperature by allowing snails to explore a gradient of temperatures, and determined that the snails preferred 23oC. I reared snails in 13oC (cold), 23oC (warm), and 33oC (hot) water to examine if water temperature would affect the snail’s period of greatest activity, behaviour, survivability, number of egg masses produced, number of eggs per mass, egg volume, egg mass viability, and incubation period. I found no differences in activity level and no difference in behaviour except snails in hot water left the water more often and crawled farther away. Snails in the hot water experienced complete mortality with an average survival of 7 days; snails in warm and cold water survived an average of 84 and 240 days, respectively. Snails in warm water produced the most egg masses, with an average 348 masses compared to 39 and 5 masses in cold and warm water, respectively. The number of eggs per mass was greatest in the cold water, with an average 11 eggs compared to 5 and 6 eggs in warm and hot water, respectively. I found no difference in egg volume between water temperatures, but mass viability was highest in warm water. The incubation period was shortest in hot water and longest in cold water. These data suggest P. wrighti grows and survives better in water temperatures at the low end of the range observed in its current habitat and may only be tolerating the warmer water. This has implications for the ecology and conservation of this species.