CHRONOBIOLOGY INTERNATIONAL, 13(2), 93-1 01 zyxw (1 996) CIRCADIAN PATTERN OF CERCARIAL EMERGENCE IN zyxw SCHZSTOSOMA MANSONZ (PLATYHELMINTHES: DIGENEA) FROM ISOLATED BZOMPHALARIA GLABRATA Tami Bogea,* Tereza Cristina Favre, Lucia Rotenberg, Helen Soares Silva, and Otavio Sarmento Pieri Laboratbrio de Ecologia e Controle de Moluscos Vetores, Departamento de Biologia, Fundaqgo Oswaldo Cruz, Av. Brasil, 4365, CEP 21045-900, Rio de Janeiro, zyxw RJ, Brad ABSTRACT The present work aimed to compare the acrophases (peak hours) of emergence of zyxwvuts Schisrosoma mansoni cercariae among isolated individuals of the snail Biomphalaria glabrata. Laboratory stocks of melanic B. glabrata from the same biotope as the zyxwvu S. mansoni strain (Belo Horizonte, Minas Ger- ais) were used. Twenty-two snails individually exposed to five miracidia were tested. Chronobiological trials were performed outdoors after an accli- mation period of at least a week. Three groups of snails were tested between November 1989 and April 1991. Cercarial emergence from individual iso- lated snails was quantified every 3 h for 3 consecutive days. In all trials, most cercariae were found to emerge during daytime (94.9%). Time series and chronograms showed recurrent peaks during the daytime. The periodo- gram suggested that 24 h was the period that best fitted cercarial emergence data in 90.9% of the snails. The single cosinor analysis confirmed 24-h rhythms in 95.5% of the snails. Acrophases of cercarial emergence among individual snails occurred between 14:15 and 17:02. They did not differ sig- nificantly. The population cosinor analysis indicated greater homogeneity in the 24-h rhythms of cercarial emergence than in the snail groups of each chronobiological trial. Acrophases of cercarial emergence occurred between 1453 and 15:27 and did not differ significantly among all trials. Data from the three trials were pooled and analyzed using the population cosinor. This statistical method indicated a homogeneity in the 24-h rhythms of cercarial Submitted August 12, 1995; returned for revision October 18, 1995; accepted November 21, 1995. *Author to whom the proofs, correspondence, and/or reprint requests are to be sent. Present address: University of Connecticut, Department of Ecology and Evolutionary Biology, 75 North Eagleville Road, U-43, Storrs, CT, 06269-3043. 93 zyxw 0 1996 International Society for Chronobiology Chronobiol Int Downloaded from informahealthcare.com by University of British Columbia on 07/22/15 For personal use only.