Pathogen diversity of the non-native narrow-clawed crayfish (Pontastacus leptodactylus) in a UK water body

Biological invasions are intrinsically linked to introducing associated symbiotic organisms, some of which can be parasitic or pathogenic. The pathogenic risk of an 'invasive parasite' (aka. exotic pathogen) stems from its potential to infect native hosts and induce behavioural change or mortality, with the pathogen potentially presenting a greater risk than the host. Conversely, parasites translocated by invasive hosts may also reduce the impact of their host, indirectly curbing the hosts impact on the invaded ecosystem. In this study, we develop a pathogen profile for the narrow-clawed crayfish, Pontastacus leptodactylus. This is a non-native species in the United Kingdom, and poses a possible risk as a sink for invasive parasites. We use histopathology, metagenomics and metratranscriptomics to outline the symbiotic diversity harboured by a P. leptodactylus population from West Yorkshire, England. We discovered several protozoan and bacterial species that appear to be putatively commensal with this invader, as well as several RNA viruses (Hepelivirales; Picornavirales; Nodaviridae, and others) that may be more pathogenic in nature. Microsporidia and Nudiviridae were absent in our population sample set, as were all metazoan obligate parasites, such as trematodes and acanthocephalans. Using the novel genomic and pathological data available to us, we have explored the evolutionary history of each symbiotic species and provided an initial assessment on the putative risk to native species.