The effects of host size and temperature on the emergence ofEchinoparyphium recurvatumcercariae fromLymnaea peregraunder natural light conditions

Abstract

AbstractThe production of cercariae from their snail host is a fundamental component of transmission success in trematodes. The emergence ofEchinoparyphium recurvatum(Trematoda: Echinostomatidae) cercariae fromLymnaea peregrawas studied under natural sunlight conditions, using naturally infected snails of different sizes (10–17 mm) within a temperature range of 10–29°C. There was a single photoperiodic circadian cycle of emergence with one peak, which correlated with the maximum diffuse sunlight irradiation. At 21°C the daily number of emerging cercariae increased with increasing host snail size, but variations in cercarial emergence did occur between both individual snails and different days. There was only limited evidence of cyclic emergence patterns over a 3-week period, probably due to extensive snail mortality, particularly those in the larger size classes. Very few cercariae emerged in all snail size classes at the lowest temperature studied (10°C), but at increasingly higher temperatures elevated numbers of cercariae emerged, reaching an optimum between 17 and 25°C. Above this range emergence was reduced. At all temperatures more cercariae emerged from larger snails. Analysis of emergence using theQ10value, a measure of physiological processes over temperature ranges, showed that between 10 and 21°C ( ≈ 15°C)Q10values exceeded 100 for all snail size classes, indicating a substantially greater emergence than would be expected for normal physiological rates. From 14 to 25°C ( ≈ 20°C) cercarial emergence in most snail size classes showed little change inQ10, although in the smallest size class emergence was still substantially greater than the typicalQ10increase expected over this temperature range. At the highest range of 21–29°C ( ≈ 25°C),Q10was much reduced. The importance of these results for cercarial emergence under global climate change is discussed.