Genetic and phenotypic characterization of immunological niche conformance in cavefish

The immune system reflects an important adaptation to the individual parasitological niche. Since host-parasite interactions strongly influence the evolution of immune systems, different parasitological niches resulted in specific immunological phenotypes of hosts. For example, cave dwelling morphotypes of the Mexican tetra Astyanax mexicanus are exposed to low parasite abundances and diversity. Consequently, these fish invest more into the specific adaptive immune system. In contrast to that, surface populations of the same species show a strong unspecific innate immune investment due to a high parasite abundance and diversity in their stream environment. This raises the question whether an immunological adaptation to a certain parasite abundance and diversity affects the ability of the host to conform also to different parasitological niches. To study this hypothesized immunological niche conformance and potential physiological and genetic underpinnings, we will use A. mexicanus as a model system. At first, we will characterize parasitological niches of various cave and surface populations of A. mexicanus in the field via screening and collecting parasites together with measuring other parameters that might affect the immune phenotype. Then we will challenge individual lab-reared fish from the same populations with parasite-supernatants from different populations that we collected in the field to examine their degree of immunological niche conformance. This will include physiological and genetic methods such as image-based flow cytometry and single-cell RNA sequencing.