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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Photoperiodic stimulation of sexual maturation in prepuberal boars and reproductive efficiency in sows.

Greenberg, Louise Gail. January 1981 (has links)
No description available.
32

Reproductive biology of the Egyptian free-tailed bat, Tadarida Aegyptiaca

Tsita, Johannes Ngoako January 1994 (has links)
The reproductive biology of Tadarida aegyptiaca was studied using specimens collected in the Cape Province of South Africa. The morphology of the reproductive tract of the species was generally similar to that of other molossids, however, the absence of Cowpers glands was unusual. Spermatogenesis began in February and spermatozoa were released to the cauda epididymis during August and September. Follicular development started in March and culminated with the appearance of Graafian follicles in July. Ovulation probably occurred in August and specimens were pregnant by September. Gestation length was estimated to be four to five months and a single young was born in December. The data suggest that T. aegyptiaca is monotocous and monoestrous.
33

The biology of reproduction of the Tete veld rat, Aethomys ineptus and the Namaqua rock mouse, Aethomys namaquensis (Rodentia: Muridae)

Muteka, Sachariah Penda 06 May 2005 (has links)
The distributional range of the Tete veld rat, Aethomys ineptus, extends from the Limpopo Province in the north through to the south of KwaZulu Natal. The Tete veld rat is a seasonal breeder, with the breeding period confmed to the wet summer months of the year in the Gauteng Province of South Africa. The seasonality of reproduction in the Tete veld rat is confirmed by reproductive tract morphometrics, ovarian histology, plasma progesterone, and oestradiol-17β in females, and testicular histology and plasma testosterone concentrations in males. The presence of some spermatogenic activity and spermatozoa in the epididymides, as well as some follicular activity and raised circulating progesterone, and oestradiol-17β concentrations in some females during winter intimates that the Tete veld rat is possibly an opportunistic breeder. Reproduction during winter is presumably restricted by food availability and adverse winter conditions. The Namaqua rock mouse, Aethomys Namaquensis, on the other hand is widely distributed in the southern African subregion. Reproductive tract morphometrics, ovarian histology, plasma progesterone and oestradiol-17β in females, and testicular histology, seminiferous tubule diameters and plasma testosterone concentrations in males confirm that the Namaqua rock mouse is a strictly seasonal breeder. The breeding period starts in October and extends to the end of February. The absence of Graafian follicles, corpora lutea, corpora albicans, corpus hemorrhagicum, lower plasma progesterone and oestradiol concentrations in females, and small seminiferous tubule diameters, and lower testosterone concentrations during winter months suggest that reproduction is completely inhibited during this period of the year. Photoperiodic responsiveness was determined in both the Tete veld rat and the Namaqua rock mouse by exposing the animals to long day (LD) and short day (SD) lengths. Testicular mass expressed against body mass, testicular volume, and seminiferous tubule diameters were significantly larger and plasma testosterone concentrations were significantly higher in males subjected to a long day photoperiod than in males exposed to a short day. These fmdings suggest that both species are photoperiodically responsive and that photoperiod could potentially play a role in reproduction in both the Tete veld rat and the Namaqua rock mouse. In conclusion, the results in this study suggest that the Tete veld rat is a seasonal breeder with the breeding period confined to the rainy summer months in South Africa. The breeding season starts in October and extends to April. Reproduction in the Tete veld rat appears to involve photoperiod. The Namaqua rock mouse is a strictly seasonal breeder with a breeding period occurring between October and the end of February. Breeding during the winter months is completely inhibited. The Namaqua rock mouse may also utilize photoperiod to initiate reproductive events. / Dissertation (MSc)--University of Pretoria, 2006. / Zoology and Entomology / Unrestricted
34

The reproductive physiology of triploid Pacific salmonids

Benfey, Tillmann J. January 1988 (has links)
Triploidy was induced in rainbow trout, Salmo gairdneri Richardson, by heat shock (10 min at 26, 28 or 30°C, applied 1 min after fertilization at 10°C) and in pink salmon, Oncorhynchus gorbuscha Walbaum, and coho salmon, 0. kisutch Walb., by hydrostatic pressure shock (1, 2, 3 or 4 min at 69,000 kPa, applied 15 min after fertilization at 10.5°C). Triploid individuals were identified by the flow cytometric measurement of DNA content of erythrocytes stained with propidium iodide. Gonadosomatic index was reduced to a much greater extent in triploid females than males. Triploid ovaries remained very small, and contained virtually no oocytes. Triploid testes became quite large, but few cells developed beyond the spermatocyte stage. Triploid male rainbow trout had significantly lower spermatocrits than diploids, and their spermatozoa were aneuploid. Growth rates were the same for diploid and triploid rainbow trout, but triploid female pink salmon were smaller than maturing diploid females and diploid and triploid males of the same age. Triploid males of both species developed typical secondary sexual characteristics and had normal endocrine profiles for plasma sex steroids and plasma and pituitary gonadotropin, but their cycle was delayed by about one month. Triploid females developed no secondary sexual characteristics and showed no endocrine signs of maturation, even at the level of the pituitary. Vitellogenin synthesis was induced in immature diploid and triploid coho salmon by the weekly injection of 17β-estradiol. Plasma vitellogenin and pituitary gonadotropin levels were significantly elevated over levels of sham-injected fish, whereas plasma gonadotropin levels were slightly depressed. There was no significant difference between diploids and triploids for any of these results, indicating that normal vitellogenesis is not impaired by triploidy per se. It is concluded that triploids of both sexes are genetically sterile, but that only triploid females do not undergo physiological maturation. Triploid testes develop sufficiently for their steroidogenic cells to become active, which is not the case for triploid ovaries. The occasional cells that pass through the normal meiotic block develop to full maturity in triploid males but not in triploid females, probably due to the absence of the appropriate stimulus to initiate and maintain vitellogenesis. Although triploids of both sexes should make valuable tools for basic research on reproductive physiology, only the females will be useful for practical fish culture to avoid the economically detrimental effects of maturation in fish destined for human consumption. / Science, Faculty of / Zoology, Department of / Graduate
35

Determinants of fitness in an island population of song sparrows

Hochachka, Wesley Michael January 1990 (has links)
Patterns and causes of variation in the reproductive success of Song Sparrows (Melospiza melodia) are investigated in this thesis. The two general patterns looked for were: inter-annual variation in reproductive success, and repeatability of reproductive success of individual parents. The specific problems addressed were: (1) whether intra-seasonal variation in reproductive success was the result of differences in the quality of parents or their territories; (2) whether nutritional condition of nestlings affected their subsequent survival; (3) whether variation in morphology of adult sparrows was influenced by the conditions under which birds grew up; and (4) given the patterns discovered in the first three sections, how trade-offs between present and future reproduction constrain the effort expended by adult sparrows in reproduction. Data used in this thesis came from a long-term (1975-present) descriptive study of the population of Song Sparrows living on Mandarte Island, B.C., Canada. Data on survival, reproductive success, and nestling and adult morphology were all available. The approach taken in the thesis was to search for systematic variation in the data, and from these patterns to make inferences about cause and effect. The following conclusions are made: (1) the intra-seasonal decline in clutch size, observed in populations of many species of birds, was the result of poor birds or birds on poor quality territories both nesting later and laying smaller clutches; (2) nestlings in better nutritional condition had a higher probability of survival while under the care of their parents, than nestlings in poor nutritional condition; (3) the probability of survival of offspring after they left their parents' care was lower for young born later in the year, but this pattern is not caused by variation among parents or their territories (contrary to the cause of seasonal decline in clutch size); (4) morphology of birds as adults was affected by the environment that birds grew up in, with nutritional condition and population density while a nestling both affecting adult morphology; (5) the effort that parents expend on reproduction is constrained by ability to vary reproductive effort with date of nesting and parental age. / Science, Faculty of / Zoology, Department of / Graduate
36

On the structure and development of the bursa ovarica and infundibulum tubae in Elephantulus myurus jamesoni : with special reference to the ovarial bursa in mammals, and to its function

Austoker, Joyce 15 October 2014 (has links)
Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, 1950.
37

Reproduction in Carditamera floridana (Conrad) (Bivalvia: Carditidae)

Unknown Date (has links)
Oviparous reproduction in Carditamera floridana was studied in St. Andrew's Sound, near Mexico Beach, Florida, between May 1992 and February 1994. The oviparous mode of development of Carditamera floridana is unique in the number of juveniles produced, the extent of parental care involved, the subtropical range of the species, and the lack of a distinct vitellogenic mechanism. / Typescript. / "1995." / "Submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Master of Science." / Advisor: William H. Heard, Professor Directing Thesis. / Includes bibliographical references.
38

Reproduction and its seasonal variation in the soupfin shark, Galeorhinus galeus

Theron, Daniel Frederick 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The soupfin shark, Galeorhinus galeus, is a circum-global shark species of great economical importance. Their reproductive biology is reasonably well understood, but intraspecific differences between global populations necessitate the study o f populations separately. For this study, 70 male and 74 female specimens were collected along the southwestern coast of South Africa between 34°8'S; 18°27'E and 34°24S; 21°25'E. Morphological changes were described and serum steroid hormone concentrations evaluated by enzyme-linked immunosorbent assay (ELISA) over an almost-complete reproductive cycle. Males display an annual spermatogenic cycle that starts with a significant peak in testosterone concentrations coinciding with the start o f spermatogenesis around April-May. Testosterone levels decrease to reach a minimum in late-winter after which spermiogenesis commences. The prevalence of spermiogenic cysts in the testis increase to reach a peak between February and April, after which mating occurs until about July. Females (aplacentally viviparous) are suggested to have a triennial cycle, similar to the Brazilian & Australian populations, but different from the Californian & Mediterranean populations. During the first year after parturition there is not much reproductive development. The following year sees increased vitellogenic activity in ovarian follicles and development of the oviducal glands and uteri. Ovulation then occurs towards the end of that year. Mating is suggested to precede ovulation by two to three months necessitating sperm storage by the females in their oviducal glands. A 12-15 month gestation ensues and ends in parturition the following summer. Testosterone and estradiol levels fluctuate together and are involved in the preparation for ovulation and oviducal gland development. Progesterone levels show two distinct peaks during the year, in both immature and mature females, and could not yet be functionally linked to any reproductive activity or condition. This cycle is not very tightly synchronised among the South African females. / AFRIKAANSE OPSOMMING: Die vaalhaai, Galeorhinus galeus, kom wereld-wyd voor en is van groot ekonomiese belang in baie lande. Die spesie se voorplantings biologie is reeds redelik deeglik ondersoek maar intraspesifieke verskille tussen verskillende wereld populasies noodsaak die bestudering van populasies afsondelik. Daar is 70 mannetjies en 74 wyfies versamel vir hierdie studie langs die Suid Afrikaanse suid-wes kus tussen 34°8'S; 18°27'E and 34°24S; 21°25'E. Morfologiese veranderinge is beskryf en serum hormoon konsentrasies is ge-evalueer deur middel van die ELISA tegniek vir 'n amper-volledige voortplanting siklus. Mannetjies vertoon 'n jaarlikse spermatogeniese siklus met 'n piek in testosteroon konsentrasies aan die begin van spermatogenese in April-Mei. Hiema daal testosteroon vlakke tot minimum vlakke in die laat-winter, waama spermiogenese begin. Die proporsie spermiogeniese siste in die testis vermeerder tot maksimum waardes bereik word tussen Februarie en April. Paring vind hiema plaas tot omtrent Julie. Wyfies (aplasentaal vivipaar) het 'n voorgestelde driejaarlikse siklus, soortgelyk aan die Brasiliaanse & Australiese populasies maar anders as die Kalifomiese & Mediterreense populasies. Tydens die eerste jaar na bevalling vind daar nie veel voortplantings ontwikkeling plaas nie. Die daaropvolgende jaar verhoog vitellogeniese aktiwiteit in die ovarium follikels en ontwikkeling van die dopkliere en uteri. Ovulasie vind nader aan die einde van hierdie jaar plaas. Paring vind heel moontlik twee tot drie maande voor ovulasie plaas, wat noodsaak dat die wyfies sperm moet stoor in hulle dopkliere. 'n 12- 15 maande dratyd begin na ovulasie en eindig in geboorte teen die volgende somer. Testosteroon en estradiol konsentrasies fluktueer saam en speel 'n rol tydens voorbereidings vir ovulasie en dopklier ontwikkeling. Progesteroon vlakke piek twee maal gedurende die jaar, in beide onvolwasse en volwasse wyfies, maar dit kon nog nie funksioneel geassosieer word met enige voortplantings aktiwiteit of toestand nie. Die siklus is nie baie nou gesinkroniseer onder die Suid Afrikaanse wyfies nie.
39

Self-cleavage of plant pathogenic RNAs

Forster, Anthony Carlyle. January 1987 (has links) (PDF)
Includes bibliography.
40

Interactions between thyroid hormones and reproductive function in prepubertal and sexually mature merino rams / by Yallampalli Chandrasekhar

Chandrasekhar, Yallampalli January 1985 (has links)
Includes bibliographical references (leaves 191-207) / xiv, 207 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Examines the interactions between thyroid hormones and male reproductive function in mature, prepubertal and post pubertal Merino rams. Hypothyroidism or hyperthyroidism was induced in these rams for 8-10 weeks and their reprodroductive endocrine axis and testis functions were assessed. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1986

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