Host-induced morphological variations in the strigeoid trematode Posthodiplostomum minimum (Trematoda: Diplostomatidae). IV. Organs of reproduction (ovary and testes), vitelline gland, and egg

— a variety of amphibian, reptilian, avian, and mammalian hosts were used in experimental development of Posthodiplostomiim minimum. Results of this study indicate that the organs of reprodviction (testes and ovary) as well as the vitelline gland and egg underwent host-induced morphological variations. Due to the lack of host specificity of P. minimwn as well as the overlap of reported egg and body sizes of species of Posthodiphstomum, it is apparent that several reported species are not valid. Throughout the Uterature, members of the trematode family Diplostomatidae have been classified and divided based upon the size and shape of the anterior and posterior testes, extent of vitelline gland, position of the ovary relative to the testes and the size of the egg (Dubois 1937, 1952, 1964, 1968, 1970). In the above cases, Dubois considered the strong host specificity supposedly demonstrated by strigeoids to be the basis for his extensive taxonomic revisions. In recent years several investigators have shown that strigeoid trematodes are not as physiologically host specific as previously suggested. Ulmer (1961) emphasized the need for additional experimental data relative to host specificity in order to assess the validity of Dubois's use of it as a major criterion for establishing taxonomic relationships. Palmieri (1973, 1975, 1976) clearly demonstrated that Posthodiplostomiim minimum is able to develop to a gravid state in many host species within all vertebrate classes except fishes. It is doubtful, however, that host specificity in a strict sense is of value in differentiating species of Posthodiplostomum. Analysis of data presented in this paper clearly indicates that testes number, size and shape, ovary position, vitelline gland distribution and egg size undergo great morphological variations when experimentally developed in amphibian, reptilian, avian, and mammalian hosts. Similar results dealing with morphological variation have been reported by Watertor (1967), Blankespoor (1971), Kinsella (1971), Campbell (1973), and Palmieri (1973, 1975). Material and Methods The material and method section of this paper has been reported by Palmieri (1976). Results and Discussions OvABY. — Five variables were analyzed in studying the ovary of adult P. minimum, namely: (length, width, cross sectional area, ratio of length to width, and the variation in the position of the ovary relative to anterior and posterior testes). A complete analysis of the above data can be found in Table 1. Variations in ovary position of P. minimum are found in Figures 1-6 and Table 2. The ovary of P. minimum commonly varies in position from anterior to the anterior testis (Figs. 1-2) to lateral (Fig. 3) or posterior (Figs. 4-6) to it. In worms recovered from all four classes of experimentally fed definitive hosts, the ovary was situated most commonlv to the left of the anterior testis 'See Part II of this study. Great Basin Nat. 37:137, 1977. 'Department of Zoology, Iowa State University, Ames, Iowa 50010. Present address. Department of Zoology, Brigham Young University, Provo, Utah 84602.