Impacts of elevated water temperatures on righting behavior and survival of two freshwater caenogastropod snails
As global temperatures rise, streams and rivers are predicted to be more severely impacted than other ecosystems, due in part to the limited mobility of aquatic invertebrates. Compared to many terrestrial animals, freshwater snails have particularly low potential for migration and thus are not expected to be able to compensate for climate warming with active dispersal. In freshwater animals, several behaviors are affected by elevated temperatures, including burrowing and escape responses, among others. This laboratory study aimed to assess the impacts of elevated temperatures on righting behavior and survival in two species of freshwater caenogastropod snails: fine-ridged elimia (Elimia semicarinata) and Shawnee rocksnails (Lithasia obovata). Righting time (the time to turn the body right-side-up when placed on the dorsal side of the shell) was assessed before beginning the experiment and again after chronic (10 day) exposure to an elevated temperature. There was no significant change in righting time at any temperature for either species, but there was significantly more failure to right within the time limit at elevated temperatures. For fine-ridged elimia, 30% of the snails failed to right in 30°C, compared to 2.5% in the control temperature (20°C). Similarly, 47.8% of Shawnee rocksnails failed to right at 27°C, while 19.4% failed to right in the 20°C group. Mortality was significantly higher at 35°C for fine-ridged elimia and 30°C for Shawnee rocksnails compared to the mortality of each species’ control group. Predicted rates of climate warming and current average temperatures suggest that fine-ridged elimia face more imminent risk of large-scale failure to right within natural populations, but the lower lethal temperature for Shawnee rocksnails suggests relatively high risk as well. These results contribute to the growing body of evidence that freshwater snails will be negatively impacted by climate warming, and may face large losses in the years to come.