Ljudevit Luka Boštjančić

• Freshwater crayfish are an ancient group of decapod crustaceans. They are keystone species of freshwater habitats acting as ecosystem engineers, trophic regulators and biodiversity indicators. At the beginning of the 20th century, a collapse of native Europe freshwater crayfish populations occurred due to the introduction of the invasive oomycete pathogen, Aphanomyces astaci Schikora (1906), causative agent of the crayfish plague disease. Later, numerous introductions of invasive freshwater crayfish species, which are latently infected with their respective Ap. astaci strains, facilitated pathogen host-jumps and accelerated the decline of European freshwater crayfish stocks. However, latent infections have also been observed in European freshwater crayfish populations. In this context, my thesis focuses on elucidating the molecular mechanisms that underly the freshwater crayfish immune response to the pathogen Ap. astaci. I analyse both the susceptible and resistant host´s gene expression patterns to elucidate molecular pathways involved in the host immune response towards Ap. astaci challenge. This led me to the discovery of novel immune response factors involved in the response towards Ap. astaci, such as antimicrobial peptides (AMPs), pattern recognition receptors (PRRs), and transcription factors. My quest to elucidate the dynamics of this host-pathogen interaction has revealed that the disease progression is correlated to the pathogen progression, which occurs in multiple stages. Moreover, I identified and characterised novel transcription factors, namely CCAAT-enhancer-binding protein (C/EBP) and Krüppel homologue 1 (Kr-h1) as candidate genes in the innate immunity. Ultimately, my research highlights the complexity of the freshwater crayfish immunity, displaying how different coevolutionary mechanisms shape our understanding of this host-pathogen interaction. These results can facilitate the innovative genomic approaches in crayfish plague disease management and conservation.