The Mycobiome of a Successful Freshwater Invader, the Signal Crayfish

Fungi and fungal-like organisms are among the most damaging pathogens for freshwater crayfish and may cause significant losses of both aquacultured and wild crayfish populations. Furthermore, the most devastating effects in wild populations are caused by fungal and fungal-like pathogens transmitted by invasive crayfish species (ICS) to native crayfish populations. Although research is often focused on pathogenic mycobiota, increasing evidence points out that mycobiota in general has an important role in biological invasions, since it can affect a number of interactions between the host and the environment. Also, the characteristics of the novel environment and the dispersal process may in turn affect the composition of invaders' mycobiota, and directly and indirectly affect their fitness and invasion success. Using ITS rRNA amplicon sequencing, we have analyzed the mycobiome of one of the most successful ICS in Europe – the signal crayfish – in the Korana River, Croatia. We explored the mycobiome of four types of crayfish samples (exoskeletal biofilm, hemolymph, hepatopancreas and intestine) and two types of environmental samples (water and sediment), and compared differences in their biodiversity and abundance between upstream and downstream segments of the signal crayfish' invasion range in Korana River. Since a very small number of mycobial features in hemolymph and hepatopancreas samples was recorded, they were excluded from further analyzes. Between the remaining sample groups, intestine showed significantly lower richness of mycobiota compared to exoskeletal biofilm, water and sediment. Beta diversity analyzes showed significant differences between mycobiomes of all four sample groups, confirming their uniqueness. Comparison between upstream and downstream river segments yielded opposite richness patterns of mycobiota for sediment (significantly higher richness downstream) and exoskeletal biofilm (significantly higher richness upstream). Furthermore, beta diversity analyzes also revealed significant differences in composition and abundance of sediment and exoskeletal mycobiota between upstream and downstream river segments, indicating that crayfish exoskeleton harbors a specific mycobiota, which is affected by parameters other than environment itself. Our findings represent the first insight into mycobiome of a successful ICS, and offer a baseline for assessing how mycobiome contributes to an invader’s overall health and its further invasion success.