Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Ohio State University, 1954. / Includes bibliographical references (leaves 87-98). Available online via OhioLINK's ETD Center

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [380]-391).

The annual testicular cycle of a teleost the lake chub (Couesius plumbeus) from a north temperate latitude (51°N) has been studied by histological and histochemical methods with a planimetric evaluation of the different spermatogenetic stages. The annual cycle is divided into five different stages and the cyclical testicular changes have been correlated with changing environmental conditions. Lobule boundary cells, considered to be homologue of the Leydig cells of higher vertebrates, have been identified, and the changes in their secretory activity have been reported. Temperature is the major environmental factor controlling the testicular cycle. The pituitary gland, through its gonadotropin(s), mediates between environmental changes and developments in the testes. Higher temperatures (16°-22°C) promote spermiogenesis and spermiation, whereas low temperatures (5°-12°C) are more conducive to gonial proliferation and the initial phase of spermatogenesis. Hypophysectomy affects the mitotic ability of the spermatogonia, completely blocks their transformation into spermatocytes and suppresses the secretory activity of the lobule boundary cells. Replacement therapy with fish gonadotropin and mammalian LH restores spermatogenesis to a large extent and maximum response is elicited with whole fish pituitary extract. It is proposed that the fish pituitary gonadotropin is similar to mammalian LH and in this species mammalian FSH is physiologically inactive in the restoration of testicular activity. Since whole fish pituitary produces a maximum response it is suggested that factors such as TSH and STH have a probable synergistic role in the testicular maturation in Couesius plumbeus. Evidence is presented that a weak endogenous rhythm of activity is partly responsible for the timing of various testicular changes. / Science, Faculty of / Zoology, Department of / Graduate

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Thesis (Ph. D.)--Ohio State University, 1974. / Includes vita. Includes bibliographical references (leaves 183-189). Available online via OhioLINK's ETD Center

The modern species concept (Mayr, 1963) stresses the interbreeding within, and the reproductive isolation between, species. However, "interbreeding" is not strictly an intraspecific characteristic since numerous interspecific hybrids have been reported, especially among the temperate freshwater fishes. In this investigation, hybridizing (interbreeding) populations of the peamouth chub, Mylocheilus caurinum (Richardson), and the redside shiner, Richardsonius balteatus (Richardson) from Stave Lake, British Columbia, were studied to determine: (1) if interbreeding between them was resulting in the swamping (lack of reproductive isolation) of their gene pools, and (2) if swamping was absent, what isolating mechanisms were operative? To detect the presence or absence of swamping, two approaches were used. The first measured shifts in means of certain morphological characters for the two species within and outside the area of hybridization. The second determined the frequency of various hybrid generations. If swamping is not occurring, the frequency of hybrid backcross individuals should decrease as backcrossing continues. Both approaches indicated that swamping is absent between Mylocheilus and Richardsonius. In the absence of swamping, isolating mechanisms between the two species were examined. Seasonal, temporal (diel), spatial, and ethological premating isolating mechanisms do not appear to be effective since Mylocheilus, Richardsonius, and their hybrids spawn at the same time and place within Devils Creek, a major spawning area in Stave Lake. Egg and fry survival of crosses involving hybrid individuals were measured under experimental conditions to determine if they serve as post-mating isolating mechanisms. F₁ hybrid males are partially sterile as demonstrated by the poor egg survival of crosses involving them. However, egg survival of hybrid females when backcrossed with Mylocheilus and Richardsonius males was comparable to the parental species' crosses. Thus, fertility is not considered an effective isolating mechanism. The experiments testing the fry survival of the parental species, reciprocal F₁ hybrids, and hybrid backcrosses to Mylocheilus(= B CM) yield a clue to what isolating mechanism prevents swamping. The fry survival of reciprocal F₁ hybrid fry do not differ significantly from Mylocheilus fry. In contrast, the survival of hybrid backcross to Mylocheilus fry is approximately 20 % less than either reciprocal F₁ hybrids or Mylocheilus fry after only 48 days rearing. Additionally, 11. 5% of the surviving BCM fry possess gross abnormalities. Thus, hybrid inferiority is demonstrated experimentally. Circumstantial evidence was also gathered from Stave Lake in 1967 which suggests the inferiority of BCM fry. Relative to Mylocheilus, BCMs were five times more abundant as fingerlings than as adults. Little information was gathered on hybrid backcrosses to Richardsonius. They, appeared scarce as fingerlings as well as adults. / Science, Faculty of / Zoology, Department of / Graduate