Host-parasite interactions between Unionicola savadiensis and freshwater mussels reveal infestation patterns and metabolic adaptations in Himalayan streams

This study investigates the complex host-parasite interactions between Unionicola mites and freshwater mussels, focusing on infestation patterns across four mussel species from two river streams. Furthermore, this study explores the metabolic adaptations of a parasitic mite infesting Himalayan freshwater mussels, focusing on producing the macromolecule 13-cis-docosenamide. Lamellidens corrianus emerged as the primary host, with environmental and morphometric factors influencing infestation dynamics. Using combined morphological and molecular taxonomy, the mites were identified as Unionicola (Myanmaratax) savadiensis, and their biochemical adaptations were explored. Metabolomics profiling highlighted the presence of 13-cis-docosenamide in gill-associated mites, indicating a potential host-specific adaptation. This compound is novel to mites and suggests a unique interaction with the host’s chemical environment. GC–MS profiling of mussels stated the presence of the precursor docosenoic acid but not the final compound, supporting the hypothesis that mites synthesize 13-cis-docosenamide from host-derived precursors. The absence of this compound in mites from accidental hosts further highlights the specificity of this metabolic adaptation. Additionally, other isolated compounds were identified as polymer additives, which are known for their toxic and endocrine-disrupting properties, exacerbating ecological threats to mussel populations. This study highlights the dual ecological pressures of parasitism and the dynamics of these organisms, advancing our understanding of freshwater ecosystems and their threats.