Invasion and evolutionary history of a generalist fish parasite.

Abstract

The introduction of non-native species can lead to the introduction of non-native parasites to their introduced range which can pose significant risk to native biodiversity. The cyprinid fish species, Pseudorasbora parva, is a well-studied example of accidental introduction to a new range; it has been accidentally introduced from China to Europe. Pseudorasbora parva has been hypothesized to have also introduced the generalist fish pathogen Sphaerothecum destruens to Europe which has been identified as a potential threat to European fish biodiversity. Due to the management implications associated with the parasite’s status (native or non-native), this work aimed at determining the S. destruens origin and distribution across its native and non-native P. parva populations, whilst also developing eDNA detection methods in order to assess the efficacy of P. parva eradication as a viable control measure for S. destruens. Due to the unique taxonomical position of S. destruens in tree of life, its mitochondrial DNA evolutionary history was also investigated to better decipher its phylogenetic position. Sphaerothecum destruens presence was confirmed in 90 % of the P. parva sampled populations from China, with a maximum prevalence of 10 %. Furthermore, the phylogenetic and demographic analysis of both the host and the parasite support the hypothesis that S. destruens has been introduced to Europe through the accidental introduction of its reservoir host P. parva. The non-native status of S. destruens in Europe has important management implications for the parasite. Furthermore, S. destruens was detected in 50 % of the P. parva samples from 7 populations in the UK and identified new potential hosts for S. destruens in the wild including chub Squalius cephalus, dace leuciscus, roach Rutilus rutilus and brown trout Salmo trutta. The environmental DNA method detected S. destruens in water samples from a P. parva eradicated site 2 years after its eradication which emphasizes that preventive measures against pathogen expansion should be implemented. The phylogenetic tree based on mitochondrial derived protein sequences revealed an interesting position for S. destruens as a sister group to Filasterea and Choanoflagellate and Metazoa group and it has the most derived mitochondrial genome among Choanozoa.