Selective Pressure on Internal vs. External Immune Defence in Tribolium castaneum - Experimental Evolution Using a Microsporidian and a Fungal Parasite
University of Giessen
Institute for Phytopathology and Applied Zoology
PhD student:
Gaining a better understanding of immune defence and how it evolves is currently one of the most interesting topics in evolutionary biology. Moreover, the combination of evolutionary immunology with host parasite co-evolution will deepen our understanding even further, as it is taking immunology out of the nut shell and back to its natural conditions. This goes in line with the recent proclamation of the hologenome theory and the importance if microbiota.
However, another until only recently neglected aspect of immune defence is the external immune defence in non-social organisms. External immune defence is an extended defence outside of the body, e.g. by behavioural changes or the secretion of antimicrobial compounds into the environment. Especially in the latter case, individuals not only act to their own benefit, but potentially also to the benefit of their offspring and of other group members. Furthermore, the external immune defence should interact with the internal immune defence to be sufficient.
The Red Flour Beetle, Tribolium castaneum, secrets broadly antimicrobial substances into the flour environment, and therefore possesses such an external immune defence. In previous work it has been shown, that under natural conditions, i.e. a parasite containing environment, this external immune defence is in balance with the internal immune defence. Consequently, in the here proposed project I ask
- whether the external immune defence is under selection by parasites, and if different parasites shift external and the classical internal immune defence in different directions.
- how external and internal immune defences are balanced, and if selection by multiple parasites will result in disruption or stabilization of this balance.
- how the balance between external and internal immune defence might be mediated, and if epigenetic effects impact on this.
This will be addressed by experimental evolution of T. castaneum with a microsporidian (Paranosema whitei) and a fungal (Beauveria bassiana) parasite, in three different concentrations each as well as a combined parasite treatment. During this experiment external (quinone secretion) and internal (Phenoloxidase activity, cuticular darkness, inhibition of bacteria and fungi) immune parameter will be estimated on the phenotypic level. Experimental evolution will be followed by transcriptomic and epigenetic (looking at DNA methylation, histone acetylation/deacetylation, microRNAs) approaches to understand how this is mediated.
Answering these questions will valuable insight into the evolution of immune defence strategies in an ecological context.