Variation in the Sizes of Eggs and Oncospheres and the Numbers and Distributions of Testes in the Tapeworm, Hymenolepis diminuta

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Abstract
Four "strains" of Hymenolepis diminuta were examined for morphological variation. These included the ARME "strain" (currently maintained at the University of Keele, U.K.), the OSU "strain" (currently maintained at The Ohio University [USA]) and the TOR (or UT) "strain" (currently maintained at the University of Toronto), all of which were derived from the parental RICE "strain," and the ANU "strain" (currently maintained at the Australian National University). Additionally, 2 separate "clonal" populations (populations derived from single cysticercoids) from both the OSU and ANU "strains" were examined. All "strains" and "clones" were maintained under identical conditions using Tenebrio molitor and male Sprague-Dawley rats as the intermediate and definitive hosts, respectively. The lenghts and widths of eggs and larvae (oncospheres) passed in the hosts'' feces, and the numbers and distribution of testes in proglottids were quantified and the data analyzed. Although analyses of the lengths and widths of eggs and larvae demonstrated significant differences among some "strains" and "clones," a discriminate analysis of the data indicated these parameters to be of questionable taxonomic significance. The eggs of all "strains" and "clones" consisted of 2 distinct populations differing in density and size but not infectivity; the relative proportions of eggs in the 2 populations were not determined. Considering all possible numbers and distributions of testes, 17 variations were seen in the strobilae of tapeworms. Analyses of the data demonstrated that the "strains" and "clones" could be differentiated clearly using only the frequencies of the 1p2a (1 poral and 2 aporal testes) or 1p3a distribution, or the frequencies of proglottids containing 3 or 4 testes; all other variations failed to clearly differentiate or group the various "strains" and "clones". The ARME "strain" was significantly less variable than the other 3 "strains," while the other three "strains" did not differ among themselves. By utilizing experiments in which holdfasts were transplanted into successive hosts, multiple strobilae that regenerated from a single holdfast were compared. The frequencies of the numbers and distribution of testes in the proglottids of strobilae that regenerated from a single holdfast were independent (i.e., differed significantly).