Foraging forms the cornerstone of an animal’s life-history. An individual's foraging success shapes the demography and health of a population. Understanding key facets of maternal foraging behaviour are crucial to get a holistic picture of both regional and local environmental factors that drive foraging behaviour. This study aimed to measure the maternal foraging behaviour of a marine top predator, the Subantarctic fur seal (Arctocephalus tropicalis), from Marion Island (MI) over a range of spatial and temporal scales. Arctocephalus tropicalis females from MI have one of the longest duration foraging trips for the species. They are most similar to conspecifics at temperate Amsterdam Island, but differ considerably from those at subantarctic Îles Crozet and Macquarie Island. Hitherto, no diving data existed for MI females. I illustrate how their diving behaviour is more similar to individuals from Îles Crozet despite their differences in foraging trip parameters. Together with Îles Crozet, MI females have one of the deepest mean diving depths (34.5 ± 2.2 m , 45.2 ± 4.8 m summer and winter respectively) and longest dive durations (70.2 ± 3 s , 104.3 ± 7.8 s summer and winter respectively) for the species. In summer, females follow the diel vertical migration of their myctophid prey. Counter intuitively, during the winter, females performed short and shallow crepuscular dives, possibly foraging on different prey. Considering that these individuals dive in deep waters, this is most likely related to myctophids occupying lower depths in the water column during winter. At dusk and dawn they are inaccessible to diving fur seals. At-sea data from multiple foraging trips per female illustrated that females have both a colony- and individual preferred foraging direction which varied seasonally. Individuals travelled consistently in the same direction regionally, but locally appear to track prey in a heterogeneous environment. The few trips in the winter to the west of MI suggest that this is a short-term response to varying prey availability rather than a long-term foraging tactic. Six years of observer-based attendance cycle data were used to augment telemetry data. Multi-state mark-recapture models were used to determine the probability of a female being missed when she was present (detection probability). Attendance data were corrected accordingly. Neither El Niño (EN) nor anomalous seasurface temperature (SSTa) influenced any of the attendance cycle parameters, as foraging trip duration is a poor predictor of weak environmental change. Only season and pup sex had a significant impact on female provisioning rates. Foraging trip duration was longer during winter than during summer. Females spent a higher percentage of time on land when they had female pups rather than male pups. Although observational attendance data remain useful it ideally requires concomitant data on pup growth, production and female body condition to elucidate changes in female provisioning rates. Temporally, season had the most influence on female foraging behaviour. Spatially, it appears that a lack of prominent local bathymetrical features overshadows MI's favourable position in the productive Polar Frontal Zone. Arctocephalus tropicalis females from MI work harder at foraging than at any other island population of conspecifics. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Zoology and Entomology / Unrestricted

It is generally thought that in amphibians, thyroid hormones (THs) regulate metamorphosis, while sex steroids (estrogens and androgens) regulate gonadal differentiation. However, inhibition of TH synthesis in frogs alters gonadal differentiation, suggesting instead that these two endocrine axes interact during development. Specifically, THs may be involved in male development, while estrogens may inhibit tadpole metamorphosis. However, we do not currently know the mechanisms that account for these interactions, let alone how such mechanisms may differ between species. To develop and test new hypotheses on the roles of sex steroids and THs, I first examined transcriptional profiles (mRNA) of enzymes and receptors related to sex steroids and THs during embryogenesis and metamorphosis in Silurana tropicalis. Tadpoles were exposed to either an estrogen synthesis inhibitor (fadrozole) or TH (triiodothyronine, T3) during early larval or tadpole development. Acute exposures of S. tropicalis to fadrozole or T3 during early development resulted in increased expression of androgen- and TH-related genes in whole body larvae, while chronic exposure to fadrozole during metamorphosis affected gonadal differentiation but did not affect tadpole development. On the other hand, acute exposure to T3 during metamorphosis increased the expression of androgen-related transcripts both in the brain and gonad. In S. tropicalis, the results suggested that cross-talk is primarily in one direction (i.e., effect of THs on the reproductive axis) with a strong relationship between TH and androgen status. Lastly, I established developmental transcript profiles and investigated T3 regulation of brain and gonad transcripts in Engystomops pustulosus. I then compared these results with S. tropicalis and an earlier study in Lithobates pipiens. While each species developed with similar profiles, they differed in their response to T3. Exposure to T3 resulted in either an increase in androgen-related genes (S. tropicalis) or a decrease in estrogen-related genes (E. pustulosus and L. pipiens). In conclusion, these data demonstrated that cross-talk mechanisms differ among these three evolutionary separate species, but in all cases, T3 appears to affect the balance of sex steroids, stimulating the androgen system and providing potential mechanisms of the masculinising effects of THs. These results will contribute to understanding the mechanisms of hormone interactions and their evolutionary basis in frogs.

Origin of mammalian somatic cells in the developing testes remains unclear. This origin could be explained by established cell culture derived from testes of Xenopus tropicalis juvenile male. The expression profile of the cell culture showed transcription of some pluripotency genes, somatic Sertoli and peritubular myoid cell markers and last but not least, the mesenchymal stem cell markers. Conversely, germ cell genes were downregulated. Immunocytochemical analysis revealed expression of Vimentin, Sox9 and α-smooth muscle actin, indicating that the testicular cell culture is a common mesenchymal progenitor of the Sertoli and peritubular myoid cells and that the cell culture did not arise from spermatogonial stem cells undergoing incomplete reprogramming in vitro. Testing of X. tropicalis cell culture during induction of differentiation in vitro revealed that these cells are probably multipotent with the ability to differentiate into adipocytes, chondroblasts and osteoblasts. The ability to derive multipotent stem cells from the juvenile testes opens new possibilities of using these cells for biotechnology and medicine. Keywords: Testicular somatic cells, Xenopus tropicalis, progenitor, mesenchymal stem cells, induction of differentiation, multipotency

The amphibian decline phenomenon now involves in excess of a third of the roughly 6000 species of amphibians on the planet. The problems that drive the declines are diverse with no end in sight. The Amphibian Conservation Action Plan (ACAP) aims to stem amphibian decline through four recommended actions by researchers and conservation biologists: (1) Expand scientific understanding of amphibian declines and extinctions; (2) continue to document amphibian diversity and ecology and how they are changing; (3) develop and implement long-term conservation programs; (4) prepare emergency response actions for eminent crises. This Dissertation focused on two of those recommendations: expanding scientific understanding of amphibian declines and extinctions and continuing to document amphibian diversity and ecology and how they are changing. The first chapter is a review of the amphibian decline phenomenon. The second, third, and fourth chapters focus on expanding scientific understanding of amphibian diversity and ecology with the description of a formerly unknown species (chapter 2), and ecological papers on two poorly known species (chapters 3 and 4). Chapter five focuses on the first ACAP recommendation in improving scientific understanding of the causes behind amphibian decline. The chapter is an experimental examination of two related species and their developmental reactions to common heavy metal contaminants. The goal of this Dissertation is to contribute toward the general amphibian knowledge base relative to the recommendations of ACAP.

Effluents of industrial wastewaters from oil refineries, paper mills, dyes, ceramic factories, resins, textiles and plastic contain high concentrations of aromatic compounds, which are toxic to organisms. Degradation of these compounds to tolerant limits before releasing them into the environment is an urgent requirement. Candida tropicalis yeast is an important representative of eucaryotic microorganisms that are able to utilize phenol. During the first phase of phenol biodegradation, cytoplasmatic NADPH-dependent phenol hydroxylase of C. tropicatis oxidizes phenol to catechol. Catechol is in the second phase of biodegradative process oxidized to cis,cis-muconic acid by the reaction catalyzed with catechol-1,2-dioxygenase. In this diploma thesis we investigated the effect of the heavy metal ions on NADPH-dependent phenol hydroxylase and catechol-1,2-dioxygenase of C. tropicalis. Phenol hydroxylase was inhibited by Cu2+ and Pb2+ ions. Catechol dioxygenase was inhibited by all substances containing heavy metal ions (Fe2+ , Mn2+ , Cd2+ , Cu2+ and Pb2+ ), which were tested in this work. The most effective inhibition was produced by Pb2+ followed by Mn2+ , Cd2+ Fe2+ and Cu2+ ions. The higher sensitivity of catechol-1,2-dioxygenase to heavy metal ions might follow from the presence of histidine residue...

Sertoli cells (SCs) are somatic cells of testicular tissue that are involved in spermatogenesis and maturation of germ cells. They are currently being extensively studied for their immunomodulatory abilities, and recent studies have shown that they share some properties with mesenchymal stromal cells (MSCs). Detailed characterization of SCs and clarification of their role in testicular tissue is crucial for potential use of SCs as a therapeutic tool in regenerative medicine. Cell culture of Xenopus tropicalis immature Sertoli cells (XtiSCs) and Mus musculus (mSCs) Sertoli cells were established in the Laboratories of Developmental Biology and Immunoregulations, Faculty of Science, Charles University. Previous research has characterized XtiSCs and demonstrated their multipotent potential by in vitro differentiation into a mesodermal line. Following this research, one of the goals of the diploma project was the induction of in vitro differentiation of XtiSC into other cell types, which would verify the differentiation potential of XtiSCs. The mSC expression profile confirmed the somatic origin of this culture as well as the transcription of Sertoli cell gene markers. Differentiation of mSCs along the mesodermal line into osteoblasts, chondrocytes and adipocytes has been successfully induced in vitro....

Sertoli cells represent the only somatic cell type within the seminiferous tubules with direct contact to germ cells. Sertoli cells significantly contribute to the development of the testicular niche in a male embryo. Their role during postnatal life is in the regulation and nutrition of germ cells and the formation of the blood-testis barrier to protect these cells. In our laboratory, we have been successful in establishing a cell line of X. tropicalis immature Sertoli cells (XtiSCs) derived from juvenile testes of X. tropicalis. The objective of this thesis was to induce the differentiation process of XtiSCs into mature Sertoli cells. In vitro experiments using several factors or primary culture from adult male X. tropicalis did not show any mature markers in differentiated XtiSCs. Another experiment using cell culture derived from pubertal mice was partially successful in the induction of the differentiation process. These results indicate that XtiSCs do have some differentiation potential into mature Sertoli cells. Part of this work was to test the ability of testicular cells isolated from juvenile males of X. tropicalis to form de novo organoids. In vitro experiments were successful when these cells were cultured in a three-layer matrigel.

The diploid amphibian Xenopus tropicalis represents a significant model organism for studies of early development, genes function and evolution. Such techniques as gynogenesis, injection of morpholino antisense oligonucleotide into fertilized eggs or transgenesis were established. In the recent ten years, many efforts have been made to complete the sequence information. X. tropicalis genome has been sequenced but the completion of its assembly only on the basis of sequence data has been impossible. Therefore, our first work was focused on one of approaches for a genome completing- genetic mapping. First of all, the genetic map of Xenopus tropicalis was established pursuant linkage and physical positions of markers. Since the map contained gaps, we developed a new method for genetic mapping based on the next generation sequencing of laser microdissected arm. Using Illumina next generation sequencing of fifteen copies of a short arm of chromosome 7, we obtained new insights into its genome by localizing previously unmapped genes and scaffolds as well as recognizing mislocalized portions of the genome assembly. This was the first time laser microdissection and sequencing of specific chromosomal regions has been used for the purpose of genome mapping. These data were also used in the evolution study of...