Curriculum Vitae
2007-present: PhD at Aquatic Ecology
Project title: Environmental modulation of host and parasite population dynamics. Supervised by Dr B. Ibelings and Prof E. van Donk
2004-2006: Master of Science in Epidemiology at the Swiss Tropical Institute, Basel,
Project title: Demographic, spatial and behavioural heterogeneities in an urban domestic dog population relevant to the planning of rabies control in Iringa, Tanzania. Supervised by Prof J. Zinsstag, in collaboration with Dr S. Cleaveland and Dr D. Knobel, Centre for Tropical Veterinary Medicine, Edinburgh, UK.
2001-2004: Bachelor of Science in Biology at the University of Basel
major: Animal and Plant Biology, minor: Medical Biology
1997-2000: Undergraduate studies at the University of Basel:
major: German literature and philology, minor: English literature and philology
Work experience:
2003-2004: Assistance to the department of public relations of the University of Basel
Maintenance of the institutional database, handling enquiries, generation of location maps
2000-2001: Volunteer Researcher at the Meerkat Research Project in South Africa, supervised by
Prof. T. Clutton-Brock (University of Cambridge, UK), and
Prof. E. Cameron (Mammal Research Institute, University of Pretoria, ZA)
Grant received:
Commission for Research Partnerships in Developing Countries (KFPE) for MSc project:
Echanges Universitaire: http://www.kfpe.ch/projects/echangesuniv/gsell.php
Projects
Small they may seem, but chytrid fungi are well able to wreak havoc on their hapless hosts. Chytrids are microscopic fungi belonging to the division Chytridiomycota and many of them are obligate parasites of bloom forming diatoms, chlorophytes and blue-green algae. Within this project I’m working with the Zygorhizidium planktonicum (parasite) - Asterionella formosa (host) model system which has been has been studied intermittently over the last 30 years, both in the laboratory and in natural populations in Lake Maarsseveen (NL). The host population shows high genotypic diversity and typically blooms twice a year, in early spring and again in early fall. These blooms are host to the chytrid parasite which is able to become epidemic at specific light and temperature conditions. During such epidemics, the parasite can infect close to 100% of the host population and thus may act as a strong selective agent on the host population by negative frequency dependent selection of host genotypes. In this case, parasitism may work to maintain genotypic diversity in the host population and being a rare genotype may pay off for the host. But this parasite mediated selection on host genotypes may be confounded by concurrent environmental variation such as seasonal temperature changes. Such environmental variation may also play a role in the maintenance host genotypic diversity, especially so if fitness responses differ between the genotypes and change in magnitude along an environmental gradient so that no genotype can outperform all others across all environments (genotype by environment interaction (GxE)).
Description of the host:
Asterionella formosa is a cosmopolitan pennate freshwater diatom. It forms star shaped colonies of typically eight cells, although colony sizes can vary from one cell up to more than twenty. The cells are attached to each other by extracellular matter at one end of the pin, form spiralling chains and are about 60-80µm long and 2-4µm wide. As is typical for diatoms, each cell is encased in a silicate shell, roughly speaking formed like a shoebox with an epitheca and a hypotheca. As the diatom reproduces, each theca forms the epitheca of the daughter cell. Thus with each division, one offspring becomes smaller and wider. Becoming smaller changes the surface to volume ratio and has implications for nutrient uptake, sinking behaviour and palatability for grazers. In order to regain their original size, diatoms have to reproduce sexually, however this has not yet been observed in A. formosa. However, there may also be other ways to rejuvenate.
Asterionella formosa colony
Description of the parasite:
Z. planktonicum is an obligate parasite of the freshwater diatoms Asterionella formosa and Synedra aquus. As all chytrids it is characterised by a motile life stage for its zoospores possess one posterior flagellum. This allows them to actively search for new hosts probably by following chemical clues. Once a zoospore has found a suitable host cell, it attaches to the host surface, develops hyphen like rhizoids and penetrates the Asterionella cell through the girdle zone. Once firmly attached it grows to a sporangium and by mitosis produces up to 25 asexually formed zoospores. When the zoospores are ripe, the sporangium dehisces and releases them. Z. planktonicum also has a sexual reproduction cycle whereby one compatible sporangium forms a conjugal tube to another one and transfers its contents to the recipient sporangium. After plasmogamy, deposition of a thicker wall is initiated and the two nuclei fuse. The zygote then enters a stage of dormancy. After germination of the thick walled resting spore, new haploid zoospores are produced by meiosis and mitosis and released by dehiscence.
Asterionella formosa colony with Zygorhizidium planktonicum sporangium
Zygorhizidium planktonicum sporangia in phase contrast
Zygorhizidium planktonicum sporangia stained with calcofluor
white under fluorescence
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