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Biased distribution of trematode metacercariae in the nephric system of Rana tadpoles

Published online by Cambridge University Press:  16 November 2000

Greg W. Thiemann
Affiliation:
Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4J1 Canada. E-mail: greg.thiemann@ns.sympatico.ca
Richard J. Wassersug
Affiliation:
Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia, B3H 4H7 Canada. E-mail: tadpole@is.dal.ca
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Abstract

Echinostoma sp. use larval anurans as intermediate hosts. The cercariae enter the tadpoles via the cloacal opening and form metacercarial cysts in the kidneys, pronephroi, and Wolffian ducts. To examine the distribution of Echinostoma metacercariae in Rana sylvatica and Rana clamitans tadpoles, 200 individuals of each species were exposed to free-swimming cercariae. There was a significant left:right bias in the distribution of metacercariae within both R. sylvatica and R. clamitans tadpole hosts, with trematodes preferentially encysting in nephric structures on the right side. In R. sylvatica and R. clamitans, respectively, 56.7% and 96.8% of the metacercariae were on the tadpoles' right side. Asymmetry in the distribution of parasites followed the direction of the asymmetry in tadpole kidney size, but was much greater. Trematodes preferentially encysted in the head kidneys of R. clamitans, which regress at metamorphosis. The right head kidney was the most commonly infected structure in R. clamitans tadpoles, containing 72.7% of all cysts in that species. Despite the preference of trematodes to encyst in the head kidney, there was no correlation between the number of cysts in the right kidney and the number in the right head kidney. This suggests that limited space in the head kidney does not influence metacercarial formation in the kidney proper. The high frequency of unilateral encystment in both anurans, and in the head kidneys of R. clamitans, may be the result of a co-evolved relationship that ultimately benefits both the host and parasite by ensuring host survival.

Type
Short Communication
Copyright
© 2000 The Zoological Society of London

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