Reconsideration of the effects of selfing on the viability of Hymenolepis nana.

A single cysticercoid of Hymenolepis nana was orally administered to an SPF-ICR strain mouse which was congenitally free of H. nana. Gravid proglottids of the resulting adult worm (parental generation) were fed to flour beetles, Tribolium confusum. Six or 14 days later, one cysticercoid from the beetles was fed to each mouse. Gravid proglottids were subsequently recovered and fed to beetles as above. This procedure was repeated for more than 20 generations. H. nana can survive repeated selfing and has been maintained for at least 27 generations. No decrease in the proportion of cysticercoids into adults with repeated selfing was observed in our experiments. Our results appear to conflict somewhat with results reported previously. This discrepancy may be due to a difference in mice used as experimental hosts, although some other causal factors, e.g. fluctuation of infective rate or difference in the varieties of H. nana strain used cannot be excluded.