Virulence, cultivating conditions, and phylogenetic analyses of oomycete parasites in Daphnia

Abstract

We describe the infectivity, virulence, cultivating conditions, and phylogenetic positions of naturally occurring oomycete parasites of Daphnia, invertebrates which play a major role in aquatic food webs. Daphnia pulex individuals were found dead and covered by oomycete mycelia when exposed to pond sediments. We were able to extract 4 oomycete isolates from dead Daphnia and successfully cultivate them. Using the ITS and LSU rDNA sequences, we further showed these isolates to be distinct species. The isolates were experimentally demonstrated to be parasitic and not saprobic. After exposure to the parasites, Daphnia mortality was much higher than that reported for Daphnia infected with other known parasite species. Therefore, it is likely that oomycete parasites are important selective pressures in natural Daphnia populations. Moreover, their close phylogenetic relationship to parasites of fish and algae suggests that the stability of aquatic food webs (i.e. fish-Daphnia-algae) might be influenced by the shared parasite communities.

Molecular Identification and Hidden Diversity of Novel Daphnia Parasites from European Lakes

“…Interestingly, both O. colligata and DP-1-19 are gut parasites (36) that are reported to be practically invisible without dissection of the host (15), whereas the MIC2 and In contrast to the importance of microsporidia, the importance of oomycete parasites has been underestimated in Daphnia populations. It has been shown recently that some oomycete parasites are highly virulent to Daphnia (53). Our phylogenetic analyses demonstrate that the SAP1 and SAP3 taxa are closely related to these recently recognized virulent isolates (e.g., isolate WM3 [ Fig.…”

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

“…Water molds generally grow faster in warmer temperatures (Nechwatal and Mendgen 2006;Wolinska et al 2008), as has been observed for this amphipod parasite (M. A. Duffy et al unpubl.…”

“…Based on sequence analysis, it is closely related to recently described Daphnia parasites from North American (Michigan and Illinois) ponds and European lakes (Wolinska et al 2008(Wolinska et al , 2009 addition, closely related strains have been described in Norway as parasites of the crayfish Aphanomyces astaci (Saprolegnia sp. VIO3839; Vrålstad et al 2009;Fig.…”

“…The partial sequence of its LSU gene was found to be nearly identical to the abbreviated Saprolegnia sp. WM 3 sequence (sequence identity of 99% [674/675]) (Wolinska et al 2008;Fig. 2b) and also closely related to Leptolegnia caudata (sequence identity of 96% [680/705]).…”

“…Oomycetes (water molds) are parasites known to cause high levels of mortality in many groups of aquatic organisms (Barron 2004;Cerenius et al 1988;Ramaiah 2006;Wolinska et al 2008). Much attention has been given to their impact on economically valuable species such as salmonids, crayfish, shrimp and oysters (Gouda and Moharram 2009;Phillips et al 2008;Unestam 1973), but their effects on amphipods are poorly known (but see Kiziewicz and Nalepa 2008;Phillips et al 2008;Unestam 1973), despite the important functional role that amphipods serve in freshwater communities, e.g., as grazers or prey for higher trophic levels (MacNeil et al 1997;Boisclair and Leggett 1989).…”