Department Aquatic Ecology

Host - parasite interactions in hybridizing Daphnia, the role of variable environments

Hybridization is a common phenomenon in both plant and animal kingdoms. Recent data suggest that hybridization is a creative force forming novel genotypes and allowing rapid adaptation to new or rapidly changing environments. For example, differences in hybrid and parental infection levels could affect the relative success of hybrids in natural populations. In hybrid and other systems, both host susceptibility and parasite infectivity commonly have a genetic basis. However, these traits are often sensitive to environmental variation, resulting in genotype-by-environment interactions, both of which have been often neglected in theoretical models and empirical studies.


In addition to these complexities, the relative fitness of various genotypes and hybrid classes may experience dynamic fluctuations due to co-evolving parasites. As parasites are selected to specialize on common genotypes or taxa, the relative fitness of rare variants may be correspondingly increased. This fitness increase may lead to formerly rare clones or taxa becoming common, and thus susceptible to attach from the evolving parasite. Over time such dynamic fitness fluctuations may result in higher genotypic and taxonomic diversity than expected under a static selection regime.

We are investigating this phenomenon using a long-term, high resolution dataset assembled in Greifensee, Switzerland, starting in 1998. Genetic data, infection status, and some morphological and life history traits have been measured on over 30,000 individual Daphnia, over the course of 12 epidemics of their parasite Caullerya mesnilli. These data are further compared with a long-term data series from monthly routine phyto-, zooplankton and lake chemistry samplings.


Additionally, in collaboration with colleagues in Germany, we have successfully extracted parasite DNA from representative rare and common clones isolated during four epidemics. Via next generation sequencing we are characterizing the genetic background of the parasite, and are thus able to investigate host-parasite interactions in unprecedented detail.