We study host-parasite systems to help our understanding of fast evolutionary change
Host-parasite interactions are associated with high selection pressures: parasites should evolve mechanisms to exploit their host, which leads to counter-adaptations by the host's immune system to reduce damage from the parasite. They are therefore ideal models to study evolution in action. We address this field using both natural populations of hosts and parasites, and with experimental evolution in the lab.
Through our research using the red flour beetle Tribolium castaneum as a model organism, we want to understand how basic characteristics of the immune system are shaped by evolution.
Specificity and memory are the hallmarks of the vertebrate’s immune system. For a long time, invertebrate immune systems were thought to completely lack these phenomena. However, this paradigm is currently being weakened (Kurtz 2005). In the flour beetle, our group has demonstrated that individuals who had been treated with heat-killed bacteria show improved survival when subsequently confronted with live bacteria. This protection was strongest when bacteria were from the same strain, indicating an unexpected degree of specificity (Roth et al 2009). Most astonishingly, protection was even transmitted across generations, leading to enhanced survival of offspring when either the mother or the father was ‘vaccinated’ (Roth et al 2010). We are currently studying the evolutionary ecology of such phenomena as well as the genetic and immunological mechanisms behind them, and therefore use a range of molecular and immunological techniques to address these questions.
With the three spined stickleback (Gasterosteus aculeatus) we are investigating how environmental variation influences population dynamics and host–parasite coevolution.
It is well established, that the evolutionary arms race of host–parasite counter adaptations is imprinted in the host and the parasite genome (genome x genome interaction, GxG). We hypothesise that environmental factors have a strong impact on host–parasite interactions and coevolution (GxGxE). With the three spined sticklebacks we are investigating a host species with a wide dispersal range, from marine and brackish waters, to freshwater lakes, streams, brooks and ditches.
In sticklebacks, the tapeworm Schistocephalus solidus is a fascinating model parasite with an extremely high degree of adaptation to its specific stickleback host. The parasite manipulates not only the stickleback immune system, but also the behaviour of its host making it vulnerable to predation by the parasite's final host, a fish-eating bird.
In our lab, we are investigating S. solidus – G. aculeatus pairs from different locations in Europe (Norway, Germany, Spain), with the aim to analyse environmental effects on host–parasite interactions and coevolution using temperature change as an environmental variable. The infected / uninfected sticklebacks are exposed to different temperature regimes in our digitally controlled aquaria facilities. Immune responses of exposed sticklebacks are investigated by means of flow cytometry and quantitative PCR.
Furthermore, we are interested in the ability of sticklebacks and their parasites, to adapt to ‘new’ environments and to environmental change. Here we investigate situations where there has been a history of anthropogenic impacts, such as the construction of new or altered water bodies, migratory barriers and pollution. We observe that sticklebacks are extremely adaptive and tolerant to environmental change, making them a dominant fish species in some places, but parasites, such as S. solidus can take advantage of the sometimes high abundance of sticklebacks in disturbed water systems.