Production and chronobiology of emergence of the cercariae of Euparyphium albuferensis (Trematoda : Echinostomatidae)

The production and the chronobiology of emergence of the cercariae of Eupar yphium albuferensis from Gyraulus chinensis experimentally infected with a single miracidium were established during 28 consecutive days from the firs t day of cercarial shedding. Moreover, the effect of a sudden change in lig ht-dark cycling was investigated. Although the daily cercarial shedding rat es show great variability, a progressive increase in cercarial production w as observed in the first weeks of the cercarial shedding periods, probably in relation to the demography of intramolluscan larval stages. Under 12:12 Light-dark cycling conditions, E. albuferensis cercariae emerged in the lig ht, and the rhythm was circadian. The sudden change in the light-dark cycle resulted in corresponding alterations in emergence patterns, which shows t hat cercarial emergence was correlated to light-dark alternation. The ecolo gical consequences of daily emergence by mobile cercariae whose target host s are organisms that regularly occur in the same habitat with the molluscan emitting host, such as those of E. albuferensis, are discussed with refere nce to the hypotheses proposed to date, and an alternative hypothesis is pr oposed.