Effect of Temperature on the Release of Proterometra macrostoma (Trematoda: Digenea) Cercariae from Their Snail Intermediate Host, Pleurocera semicarinata (Gastropoda: Pleuroceridae) at North Elkhorn Creek, Kentucky

Abstract

The effect of temperature on cercarial release has been well documented for several digenean species; however, there have been no prior studies assessing shedding of cercariae from snails infected with the azygiid, Proterometra macrostoma. Snails, Pleurocera semicarinata, were collected at the Lemon's Mill site on North Elkhorn Creek in Scott County, Kentucky during June and July 2016. Snails shedding cercariae (n = 453) were assigned to temperature treatments (10, 13, 15, 18, 20, 25, and 30°C) that were within the range of previously reported seasonal water temperatures at North Elkhorn Creek. Snails were acclimated to experimental temperatures for 3 d. Cercarial counts were then made at 0900 h daily over the next 7 d, and the average 7-d cercarial release was calculated for each snail. The minimum emergence threshold temperature for Pr. macrostoma cercarial release was determined to be approximately 13°C, whereas the minimum development threshold temperature was between 10 and 12°C. Notably, cercarial release increased with temperature up to 25°C, but declined at 30°C. Q10 values calculated from 10°C intervals were greatest at the lowest (13–23°C) temperature interval (Q10 = 16.1), and declined at the higher (15–25 and 20–30°C) intervals (Q10 = 4.3 and Q10 = 1.8, respectively). Snail survivorship within combined replicates ranged from 87.1 to 100% over the 10-d experiment, with the lowest survivorship observed at 30°C. These results are discussed with regard to climate change and global warming.