microbiome P. columella
The holobiont concept proposes a unified host-microbiota system, emphasizing their co-evolution, though its definition remains debated. In any case, the microbiota plays critical roles in the training and development of the host's immune system, while the immune system orchestrates the maintenance of key features of host-microbe symbiosis to integrate them to persist. In Pseudosuccinea columella, resistance to its natural parasite Fasciola hepatica appears genetically based and linked to high immunocompetence, even in pathogen-free conditions. Thus, differences in its microbiome, influenced by or influencing such differential host physiology are expected. However, distinguishing core from context-dependent microbiota is challenging due to environmental influences recognized from other model systems. We hypothesized that resistant P. columella exhibit a distinct, stable microbiome signature tied to their genetic/phenotypic identity across ecological contexts. We conducted a three-stage study comparing microbiomes of resistant and susceptible snails, representing different genotypes and phenotypes, across: (i) a field stage to study natural habitats, (ii) field-to-laboratory transitions to control environmental conditions throughout generations, and (iii) experimental parasite exposure. Field data showed site-specific microbiomes shaped by the environment, but resistant and susceptible snails differed even in sympatry. Field-derived lab-reared snails for two-to-four generations exhibited clearer microbiome segregation mostly based on genotypic and phenotypic identity. Indicator species analysis linked resistant snails with taxa like Niveispirillum, Aquicella, Variovorax, Diplorickettsiaceae, the plantyomycetes vadinHA49 and unclassified Babeliales from Dependentiae, that might add for host immune reactiveness. Specifically, PICRUSt2 predicted enrichment in pathways for amino acid, alkaloid, and folate biosynthesis. Experimental F. hepatica exposure disrupted microbiomes of both P. columella phenotypes within the first 4 days of infections, likely associated with immune activation. Despite similar disturbance patterns, phenotype-specific microbiome profiles persisted. In conclusion, resistant P. columella maintain a distinct microbiome signature tied primarily to phenotype, consistently observed across ecological contexts, despite strong environmental shaping.