Diversity at the population level
Chytrids are primitive fungi that parasitize on a wide group of organisms, including frogs and phytoplankton. In our study we are interested in the potential for co-evolution to shape the interactions between the chytrid Zygorhizidium planktonicum and its (diatom) host Asterionella formosa. Bi-yearly epidemics of this chytrid are observed in several Dutch lakes (but see below). The prevalence of infection commonly exceeds 90% and every infection kills the host cell, so that the impact of parasitism on the host population is severe. Genetic analysis of the population structure of Asterionella in a number of lakes indicated a high level of genetic diversity, despite the presumed absence of sex. Both parasite driven frequency dependent selection and fluctuating selection in a spatially and temporally variable environment contribute to the large genetic diversity of the diatom. Genotype x Environment interactions for temperature and nutrients, as demonstrated in experiments using isolates of Asterionella and infection experiments with the chytrid fungi support their role in maintaining genetic diversity. Currently we focus on parasite driven microevolution of Asterionella in the field, and on the interaction between disease and environmental stress factors (disease triangle) like pollutants and climate change. Climate change (mild winters without ice-cover) seem to have a large impact on interactions between Asterionella and the chytrid. The opportunities for a Asterionella spring bloom seem reduced, in its turn reducing the likelihood of epidemic level disease.
Gerla, D., Gsell, A.S., Kooij, B.W., Ibelings, B.W., Van Donk, E. & Mooij, W.M (2012). Alternative stable states and population crashes in a resource – susceptible - infected model for planktonic parasites and hosts. Freshwater Biology (online first).
Gsell A.S., L.N. de Senerpont Domis, Przytulska-Bartosiewicz, A., Mooij, M.W., Van Donk, E. & Ibelings, B.W. (2012). Genotype by temperature interactions may help to maintain clonal diversity in Asterionella Formosa (Bacillariophceae). Journal of Phycology (online first).
Gsell, A.S., de Senerpont Domis, L., Verhoeven K., van Donk, E. & Ibelings, B.W. Chytrid epidemics may increase genetic diversity of a diatom spring bloom. ISME-J (in revision).
Ibelings, B.W., Gsell, A.S., Mooij, W.M.,Van Donk, E, Van den Wyngaert, S. De Senerpont Domis, L.N. (2011). Chytrid infections of diatom spring blooms: is climate warming reducing epidemic development, and yet detrimental for the host? Freshwater Biology (Special Issue on Emerging Diseases in Freshwater Ecosystems) 56: 754-766.
Kagami, M., Von Elert, E., Ibelings, B.W., De Bruin, A., E. & Van Donk, E. (2007) The parasitic chytrid, Zygorhidium, facilitates the growth of the cladoceran zooplankter, Daphnia, in cultures of the inedible alga Asterionella. Proceedings of the Royal Society B: 274, 1561-1566.
Van den Wyngeaert, S., Gsell, A.S., Spaak, P. & Ibelings, B.W. (2012). Herbicides in the environment alter infection dynamics in a microbial host-parasite system. Environmental Microbiology (online first).