Flowers are the organs for sexual reproduction in angiosperms. Gametogenesis in floral organs leads to formation of sperms and eggs and their fertilization forms a zygote that develops into a new plant. Gametogenesis and embryogenesis involve precisely regulated biological processes controlled by complex networks of genes and pathways. In this study, AtANA1, which was identified as a redox sensitive protein in previous study, was found to be essential for embryogenesis and also plays an important role in both male and female gametogenesis. Without a functional AtANA1, embryo development is arrested after the first cell division of the zygote. The ana1 mutation also causes arrest in different steps of male and female gametogenesis. Aborting pollen and embryos caused by the ana1 mutation exhibit enhanced accumulation of reactive oxygen species and DNA fragmentation, marks of programmed cell death. Presence of aborting ana1 pollen was also found to lead to abortion of wild type pollen in the same anther, raising a possibility that the aborting ana1 pollen might release a death signal. ANA1 could be involved in an oxidative stress signaling pathway, and loss of its function triggers death of gametophytic and embryonic cells. Another important protein involved in Arabidopsis reproductive processes is PUB4, an E3 ubiquitin ligase. The pub4 mutation was previously found to cause abnormal enlargement of tapetal cells and incomplete degeneration of the tapetum layer, resulting in a defect in pollen release and conditional male sterility. In this study, we characterized PUB4’s role in controlling floral meristem determinacy. The pub4 mutation causes formation of ectopic floral organs inside of carpels/siliques. It was found that the pub4 mutation leads to ectopic expression of WUSCHEL, an important regulator which is essential for maintaining shoot apical meristem and floral meristem, which could be responsible for the flower-in-flower phenotype. PUB4 appears to work additively with AGAMOUS (AG) to control appropriate expression of the WUS gene. Three extra large G proteins (XLGs) in Arabidopsis, which interact with PUB4, also play roles in controlling tapetal cell enlargement and degeneration. However, XLGs might not function in floral meristem determinacy.

No description available.

M.Sc. (Zoology) / The alien fish parasite Argulus japonicus Thiele, 1900 has been introduced to the African subcontinent via exotic fish species. This parasite is now found widely distributed throughout the Transvaal and has assumed near epidemic proportions among fish in the Vaal River system. . Aspects of the reproduction of this parasite were studied. Infected fish from the Vaal River system were maintained in the laboratory in order to establish a stock of A. japonicus. These infected fish, together with Cyprinus carpio Linn. ,1785 from fishponds in Lydenburg, were maintained in a 2125 cubic meter culture tank. This culture of A. japonicus was maintained for more than a year from which specimens were used for experimental work and scanning electron microscopy (SEM). The morphology and anatomy of the sexual organs of both the adult male and female parasites were described. A. japonicus males have thoracic appendages which are functional during copulation. A peg is present on the pre-axial margin of the basis of the fourth thoracic limb and a socket occurs on the dorsal post-axial side of the coxa of the third thoracic limb. The conventional concept concerning copulation is that during copulation the above structures are used only as a clasping mechanism. The peg fits firmly into the socket, keeping the limbs of the male in position, while clasping dorsally round the last thoracic limbs of the female...

Graduate

No description available.

Rhabdomys pumilio, in the Eastern Cape of South Africa, does not use short day length as an inhibitory cue for reproductive activity, and, despite previous records indicating that these mice are strictly seasonal in their reproduction, litters have been found during the winters of some years,both in the Eastern Cape and in the Western Cape. This led me to believe that the reproductive activity of Rhabdomys pumilio is more opportunistic and that the cue or cues used to control reproduction are less predictable and, or more variable than the photoperiod cue used by many seasonally reproducing rodents. Two experiments were conducted, investigating the influence of low ambient temperature (15⁰C)and reduced food availability on the reproductive activity of both male and female four striped field mice. Mice were maintained in one of four conditions (food restricted at 15⁰C, food restricted at 26⁰C, ad lib. food at 15⁰C, and ad lib. food at 26⁰C) for 4 (males) and 8 weeks (females)(photoperiod 12L:12D, humidity 40%). Results indicated that the males reduced their reproductive activity slightly when exposed to either low temperature or low food availability and that maximum inhibition of reproduction occurred when mice were exposed to both low temperature and low food availability. However, female reproductive activity was inhibited when exposed to low food availability, irrespective of the temperature. Both sexes of mice showed varying abilities to resist fat loss and, in the males, the size of the fat store had a significant effect on reproduction. This varying ability to resist fat loss could be related to levels of activity and in the females (where activity was quantified), high activity scores were significantly associated with reproductive inhibition. These results support the hypothesis that reproduction in Rhabdomys pumilio is opportunistic and controlled by the availability of energy. I propose that the females will be more sensitive to reproductive inhibition due to their far greater post-fertilization responsibilities, where the reproductive activity of the females is rapidly inhibited by a reduction in food availability, while the males are less readily inhibited by low food availability or low temperature, unless the change in the controlling factors is severe enough, or prolonged, at which stage their reproductive activity will cease. The significance of opportunistic reproduction in the seasonal but unpredictable climate of the study area is discussed.

In honeybees (Apis mellifera L.) the queen monopolises reproduction. However, especially after queen loss, workers can lay eggs, but are unable to mate. They produce haploid male offspring (drones) from unfertilised eggs via arrhenotokous parthenogenesis. In contrast, workers of the honeybee subspecies Apis mellifera capensis Eschscholtz typically produce diploid female offspring from unfertilised eggs thelytokously. After queen loss and without queen-derived brood A. m. capensis colonies can successfully requeen from worker-derived brood. This, however, is a relatively rare event in wild populations. Moreover, workerderived queens were described to be smaller, more worker-like and reproductively inferior. On the other hand, the fixation of the thelytokous trait relies mainly on sufficient numbers of viable drones produced by worker-derived queens. Small numbers of reproductively inferior worker-derived queens in A. m. capensis populations would be clearly counterintuitive. It is therefore necessary to quantify the significance of worker-dependant queen rearing pathways on the individual (queen) and on population level.Reproductive inferiority of worker-derived queens could not be confirmed on the individual (queen) level when comparing parameters indicating potential reproductive success of queen- and worker-derived queens. Queen- and worker-derived queens clearly showed a congruent range of reproductive performance. In queen rearing preference tests, increased acceptance of worker-derived female larvae was exactly counterbalanced by increased mortality, resulting in an equal number of eclosing virgin queens from an equal number of grafts in both test groups. Larval survival and successful eclosion is a prerequisite for a queen’s reproductive success. I found no difference in eclosion success for queen- and worker-derived virgin queens, indicating a similar potential for reproductive success in both queen types. Assessments of the developmental patterns of colonies headed by both queen and worker-derived queens in long-term experiments revealed no significant differences in reproductive success. Colonies headed by queen-derived queens and colonies headed by worker-derived queens could not be separated when comparing the different developmental pathways observed or from differences in worker-force. Reproductive dominance in A. m. capensis appeared tobe determined by a function of relative compositional and absolute quantitative pheromonal patterns, where individuals, which produce compositionally most queen-like blends in highest quantities, occupy top positions. Queen- and worker-derived virgin queens occupied intermediate positions between pseudoqueens and mated queens. However, no significant differences between the pheromonal status of queen- and worker-derived virgin queens were observed, suggesting a similar range of reproductive dominance for both queen types. In behavioural bioassays queen- and worker-derived virgin queens appeared to be similarly attractive to clustering workers and to drones in a drone congregation area, indicating no differences in potential reproductive success for queens from both origins for those parameters. The significant influence of the queen substance 9-ODA on attractiveness to workers and drones was confirmed. Rare requeening events from worker-derived female brood in queenless A.m. capensis do not satisfactorily explain the fixation of the thelytokous trait at a population level. I observed A. m. capensis worker ovipositing into empty artificial queen cell cups in queen-right colonies. The queen was confined behind a queen excluder grid in a separate compartment of the colony, to imitate reduced pheromonal flow, similar to swarming or superseding colonies. Eggs oviposited by workers in artificial queen cell cups were readily accepted for queen rearing and successful eclosion of viable virgin queens was observed. Consequently I suggested an alternative worker-dependant reproductive pathway in A. m. capensis, which was never described before: In swarming or superseding queenright colonies, laying workers may directly compete with the queen for reproductive success by ovipositing (instead of the queen) into natural queen cell cups. At a population level this reproductive tactic may result in large numbers of worker-derived queens of high reproductive quality in natural populations of A. m. capensis.

Seasonality of reproduction in common dolphins (Delphinus delphis), bottlenosed dolphins (Tursiops aduncus), striped dolphins (Stenella coeruleoalba) and humpbacked dolphins (Sousa chinensis) was examined using standard light microscope techniques. In the males four stages of testicular development could be identified. Individuals less than 2.26m in length and 105kg in mass had testes that contained small seminiferous tubules (0.048mm ± O.Olmm in diameter) and were classified either as juveniles (gonocytes present) or inactive (no gonocytes). Adults whose testes contained spermatozoa were said to be in late spermatogenesis while those whose testes contained no spermatids or spermatozoa were referred to as being in early spermatogenesis. In the males of D. delphis, T. aduncus and S. chinensis, late spermatogenesis occurred throughout the year and there was no significant difference in the monthly mean seminiferous tubule diameters (p > 0.05) within species. I conclude therefore that in these three species spermatogenesis is aseasonal. No conclusions about seasonality of spermatogenesis could be made for S. coeruleoalba owing to the small sample size. Large Graafian follicles occurred in the ovaries of all four species in most months of the year. However, the presence of Graafian follicles can not be taken as an indication of timing of reproduction since they may be remnants of follicles that have not yet degenerated. In D. delphis, T. aduncus and S. coeruleoalba luteal bodies (corpora albicans or corpora lutea) occurred in most months of the year. Active corpora lutea will be present in all months, in some members of the population, since gestation is approximately 12 months. The sperm structure of D. delphis was examined by scanning electron microscopy. The sperm of D. delphis is essentially similar to that described for two other species of Cetacea (Physeter catodon and Tursiops aduncus), having an ellipsoidally shaped head and a short mid-piece with nine mitochondria. The sperm dimensions for D. delphis were head length, 4.4pm; head width, 2.0pm and mid-piece length, 2.4pm. An analysis of foetal age in D. delphis showed that the majority of the foetuses were conceived in January with birth occurring the following summer (December), suggesting that reproduction is seasonal. Neonates of T. aduncus were found throughout the year suggesting aseasonal reproduction. Foetal material was not available for S. coeruleoalba and S. chinensis. Seasonality of reproduction in the four species of dolphins studied has been discussed in relation to feeding, migration and worldwide distribution of the species.

Sexuality in seabreams (Sparidae) is considered to be more complex than in any other family of fishes. Early work indicated five reproductive styles within the family: protandry, protogyny, simultaneous hermaphroditism, rudimentary hermaphroditism and gonochorism. More recently two reproductive styles have been suggested: sex change (protandry and protogyny) and secondary gonochorism (rudimentary hermaphrodites). The need for detailed descriptions of sex differentiation, gonad development and spawning behaviour in this family has been identified by a number of workers in this field. The aims of the present study were: i) to provide accurate, detailed descriptions and comparisons of gonadal development in representatives of each reproductive style, ii) to investigate their spawning strategies, and iii) to relate these findings to current theories on hermaphroditism and sex change in fishes. Four species were investigated. Slinger, Chrysoblephus puniceus, the only known protogynous hermaphrodite in Natal. Santer, Cheimerius nufar, described in the literature as a rudimentary hermaphrodite. Riverbream, Acanthopagrus berda suspected to be a protandrous hermaphrodite. Natal stump nose, Rhabdosargus sarba, reported elsewhere as a protandrous hermaphrodite. Detailed histological analysis showed that morphological and cytological development of all gonads proceeded initially in a female direction, irrespective of reproductive style, but that differentiating gonads of protandrous and protogynous hermaphrodites could easily be distinguished from one another. Early gonadal development was similar in R. sarba and A. berda with gonadal primordia differentiating into distinctly bisexual organs. In C. puniceus and C. nufar gonadal primordia differentiated into ovaries with reduced, inert male elements in the tunica albuginea. Sex differentiation occurred relatively late (100-150mm fork length) in all the species investigated. Few cells conforming to primordial germ cells (PGC's) described in other teleosts were identified. These cells only became evident after the appearance of gonial cells and their identity is questioned. Gonial cells appeared to develop within less-electron-dense cysts of cells. Gonial cells in presumptive male and female elements could not be distinguished from one another morphologically, suggesting the bipotentiality of these cells. All R. sarba and A. berda gonads pass through a predominantly male phase and all fish function first as males, indicating protandrous sex change in both species. All C. puniceus and C. nufar gonads develop initially into ovaries. Sex change thus occurs in both species and protogyny in C. puniceus is confirmed. In C. nufar, sex change may occur before or after sexual maturity and its reproductive style remains uncertain. Investigations into the spawning habits of A. berda have shown that this species spawns inside the Kosi estuary at night. Eggs are released during peak ebb tides. Spawning occurs in large aggregations and several to many males compete to spawn with individual females. This spawning strategy does not conform to predictions made from the size advantage model for protandrous species. Chrysoblephus puniceus appears to have preferential spawning sites on down-current outer reef margins. Spawning was not observed in this species, but changes in behaviour, social structure and colour during the spawning season suggest that it may have a mating system similar to several protogynous labrids and scarids, in which territories are temporary. Cheimerius nufar has a similar mating system. Temporary territories are established by large males during the spawning season, which extends from August to November. Mating is by pair-spawning and dominant territorial males obtain a disproportionate number of matings. 'Streaking' appears to represent an alternative mating strategy for males until they attain a sufficient size to establish and defend territories. The mating pattern of C. nufar suggests that it is either a gonochorist which does not conform to current theoretical predictions; or that it is a protogynous hermaphrodite incorrectly diagnosed as a rudimentary hermaphrodite; or that protogyny in the Sparidae is an ancestral condition and C. nufar is in the process of evolutionary change from a protogynous to a gonochoristic form (or visa versa).

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