Differential infection of exotic and native freshwater amphipods by a parasitic water mold in the St. Lawrence River

Abstract

A parasitic water mold (oomycete) of unknown origin was discovered infecting live native and exotic freshwater gammarid amphipods (Gammarus fasciatus and Echinogammarus ischnus, respectively) in the upper St. Lawrence River. Infections were associated with rapid die-offs of natural populations of amphipods, especially the exotic E. ischnus. Analysis of sequences of three different segments of the rRNA gene cluster indicated that the parasite was in the Saprolegniaceae family, and is related to other crustacean-associated Saprolegniaceae. Specific primers were designed based on the SSU rRNA gene and utilized for semi-quantitative analysis of parasite presence in live and dead amphipods. In laboratory experiments, infection prevalence was higher in E. ischnus individuals than in native amphipods. In addition, dead E. ischnus individuals exhibited more intense infections than G. fasciatus individuals. In contrast to the Great Lakes where E. ischnus has replaced G. fasciatus at many locations, the native species remains abundant in the St. Lawrence River more than a decade after invasion by E. ischnus in the late 1990s. We hypothesize that the parasite is facilitating the co-existence of the two amphipod species by reducing the abundance of E. ischnus in environments in which it might otherwise be dominant.

Aquatic invasive species: challenges for the future

“…Although less studied, parasitism also reduces invasion success. For example, an oomycete parasite reduced the abundance of an invasive amphipod and allowed coexistence with another native species of amphipod in a Canadian river (Kestrup et al, 2009). Most of these studies support the role of biotic resistance in reducing, and sometimes excluding, invasive species in their novel habitats.…”

The ecology and phylogeny of oomycete infections in Asplanchna rotifers

“…Attempts at cultivating a different oomycete parasite (isolated from infected amphipods) were successful, indicating that the Asplanchna ‐associated species is recalcitrant to cultivation methods that have worked for other zooplankton (Wolinska et al. , 2008) and crustacean (Kestrup et al. , in press) hosts.…”

“…In addition, peptone yeast‐extract glucose seawater agar (PYGSA) and glucose yeast‐extract seawater agar (GYSA) were modified for freshwater organisms and culturing was attempted, according to Hatai & Lawhavinit (1988). As a positive control for our infection protocols, we used the same techniques to grow an oomycete parasite isolated from infected amphipods (Kestrup et al. , in press).…”

Environmental tolerance of three gammarid species with and without invasion record under current and future global warming scenarios

“…() reported the same problem suspecting that the population might be infected by parasite or some disease, reducing the immune system of individuals. Kestrup, Thomas, van Rensburg, Ricciardi, and Duffy () observed high mortality of amphipods in the St. Lawrence River caused by parasitic oomycete (water mold), while microphallid trematodes and microsporidia were also reported in amphipods (MacNeil et al., ; Mouritsen, Tompkins, & Poulin, ). Another explanation could be cannibalism among individuals within replicates (Wijnhoven et al., ).…”