Variations in Infections of Diplostomum flexicaudum (Cort and Brooks, 1928) in Snail Intermediate Hosts of Different Sizes

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Abstract
Infections with this strigeoid trematode were studied in host spp. that varied greatly in size, viz., Fossaria abrussa, Stagnicola emarginata, Stagnicola palustris, and Lymnaea stagnalis. They were also compared in juveniles and adults of F. abrussa and S. emarginata. In the smaller snail hosts fewer daughter sporocysts were produced by the mother sporocysts, and they were smaller in size. Even in the smallest hosts all the daughter sporocysts that escaped from the mothers developed normally and produced cercariae. Infections were no more injurious in the smallest snails than in the largest ones. It is suggested that in the smallest snails the mother sporocysts of D. flexicaudum are in some way prevented from producing more daughter sporocysts than can develop normally. In large adults of L. stagnalls the numbers of daughter sporocysts produced by the mothers are many times the numbers in the smallest juveniles of F. abrussa and S. emarginata and they grow to a much greater size. This adapting of infection size to host size is probably a general phenomenon in the digenetic trematodes, permitting a given sp. to utilize hosts of very different sizes and to develop normally in very small juveniles as well as in adults of a host spp.

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