External immune defence and its integration into the classical immune system
(Collaboration with Simon Tragust, University of Halle, and Heike Feldhaar, University of Bayreuth, Germany)
In recent years, evidence has accumulated that antimicrobials not only act internally but are also deployed to the environment of an individual. Given that these antimicrobials form a defence against microbes, they should be considered part of the immune system. In addition to antimicrobials, any trait affecting the pathosphere and microbial composition in an organism’s environment forms part of an external immune defence. Antimicrobials can be self-produced, symbiont derived, or environment derived. A genetic basis and heritable variation for self-produced antimicrobials can be assumed but needs to be shown. Therefore, to understand the evolution of the external immune defence involving the environment and symbiont-derived antimicrobials, investigations have to focus on the traits leading to the acquisition of symbionts or the collection of antimicrobials and their variation.
External immune defences might include not only the use of antimicrobials but also behavioural adaptations, such as sanitary behaviours. Both are intimately linked because behavioural adaptations are required to apply and distribute secreted compounds. By identifying antimicrobials and behaviours as traits of the external immune defence, we use a tractable experimental framework in which costs and benefits for each individual can be assessed. Thereby, we also integrate the idea of social immunity where immune services are aimed at related group members as well as non-immunological defences into our definition of external immune defence. External immune defences defining an individual’s microbial environment can be viewed as the mechanisms leading to an extended immune phenotype. link to paper