Hosts, symbionts and parasites - beyond pairwise interactions
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
Probably every living organism has to face off a multitude of different parasites and pathogens. In response to the diversity of these parasites, immune systems have repeatedly diversified. Additionally, many organisms, especially arthropods, rely on symbiotic bacteria that provide additional defences against different parasites and pathogens and, similar to the body’s own immune system, can do so in a specific manner. The main focus of this project was to test whether symbiont are also subject to similar evolutionary processes. More specifically, I focused mainly on whether parasitoids and symbionts drve each other’s diversity, using aphids, their symbionts, and their parasitoids, which represent a well-studied model system for host-parasitoid-symbiont interactions. In a field survey, we investigated patterns of symbiont and parasitoid diversity and indeed found a positive association between them. Albeit these findings are correlational, they are in line with our hypothesis that parasitoids drive symbiont diversity and/or vice versa. Using an experimental evolution approach, we directly showed that parasitoid diversity can be crucial in maintaining symbiont diversity. We tested such a scenario both within a single parasitoid species, using different genotypes and between different species of parasitoid wasps. Surprisingly, results were much clearer when using a single species indicating that the composition of parasitoids may play a crucial role when it comes to driving symbiont diversity and composition. In order to test directly whether symbionts can also drive parasitoid diversity, we conducted a field experiment exposing aphid communities, which differed only in their symbiont composition and diversity, to natural parasitoid communities. Surprisingly, we observed little symbiont induced protection in this experiment and no indication that symbiont diversity enhanced parasitoid diversity. Similarly to differences in the outcome of our experimental evolution experiments, however, the exact parasitoid assemblage may play an important role and further investigations would be necessary to truly rule out that symbiont diversity does influence parasitoid communities. Taken together, our findings strongly suggest that parasites and pathogens can indeed play an important role in driving and maintaining symbiont diversity similarly to the role they play with regards to a host’s own immune system. This has far-reaching ecological and evolutionary consequences and indicates that similar processes such as red queen dynamics are at play that also shapes the interactions between these antagonists. Natural patterns of symbiont and parasitoid diversity are in line with this idea and suggest that these processes do indeed play an important role in shaping and maintaining natural symbiont communities. https://www.eawag.ch/de/news-agenda/newsplattform/news/der-vielfalt-von-symbionten-auf-der-spur/
Publications
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(2019) Diversity begets diversity: Do parasites promote variation in protective symbionts? Current Opinion in Insect Science, 32: 8-14
Hafer, N. & C. Vorburger
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(2020) Parasitoids as Drivers of Symbiont Diversity in an Insect Host. Ecology Letters
Hafer-Hahmann, N. & C. Vorburger
