Baseline histopathological survey of a recently invading island population of ‘killer shrimp’, Dikerogammarus villosus

Abstract

Dikerogammarus villosus, an invasive amphipod, has recently been detected in UK freshwaters. To assess the potential for pathogen introduction with the invader, a year-long histopathology survey of the D. villosus population inhabiting the initial site of detection (Grafham Water, Cambridgeshire, UK) was conducted. Additional samples were collected from 2 other subsequently identified populations within the UK (Cardiff Bay and Norfolk Broads), and from established populations in France (River Rhine) and Poland (River Vistula). The data revealed a range of pathogens and commensals. Several pathogens occurring within continental populations were not present within the UK populations. Microsporidian parasites and a novel viral pathogen were amongst those not observed in the UK. The absence of these pathogens at UK sites may therefore impart significant survival advantages to D. villosus over native fauna, thereby increasing its success as an invader. The contrast in pathogen profile between UK and continental-invasive populations of D. villosus provides preliminary evidence for so-called 'enemy release' in UK populations of D. villosus and is suggestive of single-point introductions, rather than continual incursion events as previously observed throughout its continental invasive range. This baseline survey provides important data on the pathogen and commensal profile of a high-impact, invasive species early in its invasion history of the UK. It can be utilised to assess potential for temporal pathogen acquisition by non-native invasive aquatic species and to investigate competitive advantages placed upon this invader due to absence of important pathogens experienced within its native range.

Enemy release and genetic founder effects in invasive killer shrimp populations of Great Britain

“…This is particularly important, given fears that D. villosus will, in future, be carried across the Irish Sea to Ireland and the Isle of Man, and across the Atlantic to North America (Dick et al 2002;Casellato et al 2007). Recent histological analysis detected no evidence of infection with microsporidian parasites in two of the four known British populations of D. villosus (Cardiff Bay and Barton Broad) (Bojko et al 2013). A single microsporidian infection was discovered in a very large sample of D. villosus (N = 1,937) from a third British population (Grafham Water) but this parasite bore little resemblance to microsporidia known from the native range of D. villosus, suggesting that it may have been acquired locally (Bojko et al 2013).…”

“…Recent histological analysis detected no evidence of infection with microsporidian parasites in two of the four known British populations of D. villosus (Cardiff Bay and Barton Broad) (Bojko et al 2013). A single microsporidian infection was discovered in a very large sample of D. villosus (N = 1,937) from a third British population (Grafham Water) but this parasite bore little resemblance to microsporidia known from the native range of D. villosus, suggesting that it may have been acquired locally (Bojko et al 2013). Microsporidian infections of amphipods can involve low numbers of parasites and such light infections may be overlooked during histological analysis.…”

“…Unusually, the colonisation history of this Ponto-Caspian species in Europe is well-documented (Wattier et al 2007). D. villosus is now wellestablished in major European river basins including the Danube, Vistula, Elbe, Oder, Rhine, Rhone, Seine and Loire, and has recently colonised Great Britain, occurring at four separate sites in southern England and Wales (Bojko et al 2013;MacNeil et al 2010).…”

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

“…Often, the pathogens of invasive hosts are little known or cryptic, requiring dedicated screening efforts to elucidate underlying parasites and pathogens that may be vectored to new habitats by non-native species (NNS) [2, 3]. …”

Enhanced fecundity and parasite release in the first amphipod invader on the Iberian Peninsula

“…Similarly, histopathology (Bojko et al, 2013) and PCRbased (Arundell et al, 2015) studies of UK populations of the invasive amphipod Dikerogammarus villosus showed a distinct lack of pathogens and parasites when compared in invasive range across central (Etxabe et al, 2015) populations of D. villosus is suggestive of single-point introductions, rather than continual incursion events as previously observed throughout its continental invasive (Bojko et al, 2013). In contrast, Dikerogammarus haemobaphes, presents UK populations with high prevalence of parasites, such as the Microsporidia Dictyocoela berillonum and Cucumispora ornate (Bojko et al, 2015) or the Nematoda Hysterothylacium deardorffoverstreetorum (Etxabe et al, 2015).…”