Pathogens of Dikerogammarus haemobaphes regulate host activity and survival, but also threaten native amphipod populations in the UK

Dikerogammarus haemobaphes is a non-native amphipod in UK freshwaters. Studies have identified this species as a low-impact invader in the UK, relative to its cousin Dikerogammarus villosus. It has been suggested that regulation by symbionts (such as Microsporidia) could explain this difference in impact. The effect of parasitism on D. haemobaphes is largely unknown. This was explored herein using 2 behavioural assays measuring activity and aggregation. First, D. haemobaphes were screened histologically post-assay, identifying 2 novel viruses (D. haemobaphes bi-facies-like virus [DhbflV], D. haemobaphes bacilliform virus [DhBV]), Cucumispora ornata (Microsporidia), Apicomplexa, and Digenea, which could alter host behaviour. DhBV infection burden increased host activity, and C. ornata infection reduced host activity. Second, native invertebrates were collected from the invasion site at Carlton Brook, UK, and tested for the presence of C. ornata. PCR screening identified that Gammarus pulex and other native invertebrates were positive for C. ornata. The host range of this parasite, and its impact on host survival, was additionally explored using D. haemobaphes, D. villosus, and G. pulex in a laboratory trial. D. haemobaphes and G. pulex became infected by C. ornata, which also lowered survival rate. D. villosus did not become infected. A PCR protocol for DhbflV was also applied to D. haemobaphes after the survival trial, associating this virus with decreased host survival. In conclusion, D. haemobaphes has a complex relationship with parasites in the UK environment. C. ornata likely regulates populations by decreasing host survival and activity, but despite this benefit, the parasite threatens susceptible native wildlife.

Parasites, pathogens and commensals in the "low-impact" non-native amphipod host Gammarus roeselii

Background

Whilst vastly understudied, pathogens of non-native species (NNS) are increasingly recognised as important threats to native wildlife. This study builds upon recent recommendations for improved screening for pathogens in NNS by focusing on populations of Gammarus roeselii in Chojna, north-western Poland. At this location, and in other parts of continental Europe, G. roeselii is considered a well-established and relatively ‘low-impact’ invader, with little understanding about its underlying pathogen profile and even less on potential spill-over of these pathogens to native species.

Results

Using a combination of histological, ultrastructural and phylogenetic approaches, we define a pathogen profile for non-native populations of G. roeselii in Poland. This profile comprised acanthocephalans (Polymorphus minutus Goese, 1782 and Pomphorhynchus sp.), digenean trematodes, commensal rotifers, commensal and parasitic ciliated protists, gregarines, microsporidia, a putative rickettsia-like organism, filamentous bacteria and two viral pathogens, the majority of which are previously unknown to science. To demonstrate potential for such pathogenic risks to be characterised from a taxonomic perspective, one of the pathogens, a novel microsporidian, is described based upon its pathology, developmental cycle and SSU rRNA gene phylogeny. The novel microsporidian Cucumispora roeselii n. sp. displayed closest morphological and phylogenetic similarity to two previously described taxa, Cucumispora dikerogammari (Ovcharenko & Kurandina, 1987), and Cucumispora ornata Bojko, Dunn, Stebbing, Ross, Kerr & Stentiford, 2015.

Conclusions

In addition to our discovery extending the host range for the genus Cucumispora Ovcharenko, Bacela, Wilkinson, Ironside, Rigaud & Wattier, 2010 outside of the amphipod host genus Dikerogammarus Stebbing, we reveal significant potential for the co-transfer of (previously unknown) pathogens alongside this host when invading novel locations. This study highlights the importance of pre-invasion screening of low-impact NNS and, provides a means to document and potentially mitigate the additional risks posed by previously unknown pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2108-6) contains supplementary material, which is available to authorized users.