Incompatibility of Protopolystoma xenopodis (Monogenea: Polystomatidae) with an octoploid Xenopus species from southern Rwanda.

Protopolystoma xenopodis is an oviparous monogenean occurring as an adult in the urinary bladder of the clawed toad Xenopus laevis. Oncomiracidia invade the host's kidneys where juveniles develop, subsequently migrating to the definitive site. In central Africa, the tetraploid X. laevis occurs in sympatry with octoploid congeners, including Xenopus wittei, believed to be the hybrid derivatives of X. laevis- and Xenopus fraseri-like parental lineages. Twenty laboratory-raised, naive specimens of an X. wittei-like species from southern Rwanda were each exposed to 30 embryonated P. xenopodis eggs (at 20 degrees C) and screened for parasite egg production until 9 months post-exposure. These toads failed to support the development of gravid parasites (comparable experimental procedures produce at least 35% prevalence of patent infection in the natural host X. laevis). Further X. wittei aff. (n = 26) and X. laevis (n = 17) were exposed to P. xenopodis oncomiracidia and dissected at variable times post-exposure: larvae were able to invade the kidneys of X. wittei aff. and began feeding and morphological development. Severe mortality of juveniles occurred in both natural and unnatural hosts between invasion and 39 days post-exposure. However, while small numbers of parasites persisted in X. laevis, no stages were found in X. wittei aff. beyond 39 days. Present data demonstrate the incompatibility of P. xenopodis with X. wittei aff. and are consistent with a hypothesis that specificity in Protopolystoma-Xenopus systems is determined primarily by the ability of juveniles to complete development in the host's kidneys.