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

Abstract

Parasites play important roles in local population dynamics and genetic structure. However, due to insufficient diagnostic tools, detailed host-parasite interactions may remain concealed by hidden parasite diversity in natural systems. Microscopic examination of 19 European lake Daphnia populations revealed the presence of three groups of parasites: fungi, microsporidia, and oomycetes. For most of these parasites no genetic markers have been described so far. Based on sequence similarities of the nuclear small-subunit and internal transcribed spacer (ITS) rRNA gene regions, one fungus, four microsporidian, and nine oomycete taxa were discovered in 147 infected Daphnia (and/or three other zooplankton crustaceans). Additionally, cloning of rRNA gene regions revealed parasite sequence variation within host individuals. This was most pronounced in the ITS region of one microsporidian taxon, where the within-host sequence variation ranged from 1.7% to 5.3% polymorphic sites for parasite isolates from 14 different geographical locations. Interestingly, the parasite isolates from close locations grouped together based on sequence similarities, suggesting that there was parasite dispersal. Taken together, the data obtained in this study revealed hidden diversity of parasite communities in Daphnia lake populations. Moreover, a higher level of resolution for identifying parasite strains makes it possible to test new hypotheses with respect to parasite dispersal, transmission routes, and coinfection.During the last decade, microparasites of Daphnia species, which are small zooplankton crustaceans, have become a popular study system in ecological and evolutionary research (for a review, see reference 15). It has been shown both in the field and under controlled laboratory conditions that parasites have a substantial impact on Daphnia fitness (7, 21, 52). Parasiteinduced reductions in Daphnia population density (11,12) or even population crashes (17) might result in disruptions of aquatic food webs, as daphnids play important roles as main phytoplankton grazers and as a major food of planktivorous fish (27). Moreover, as infections are often genotype specific (6, 8), they can lead to changes in the gene pool of a Daphnia population (7,14), sometimes significantly increasing the genetic diversity of the host population (12, 54). Thus, Daphnia parasites cause not only ecological but also evolutionary changes in aquatic systems.Conclusions regarding the importance of parasites in natural systems require powerful tools to detect and properly identify parasite taxa. Thus far, few species-specific molecular markers have been developed for Daphnia parasites (33, 38, 39, 41) and then used in experimental studies (3). In surveys of natural Daphnia populations, parasite identification has been based primarily on microscopic examination (4, 5, 29, 52), with only one exception (32). The parasites recorded in natural populations of Daphnia are thus considered members of certain taxa, or even species, without genetic confirmation. The fac...

Prior residency does not always pay off – co-infections inDaphnia

“…(family Hemiascomycetes, Wolinska et al 2009). Both parasites are common in lakes throughout Europe (Wolinska et al , 2009) and have been observed sympatrically (Wolinska et al, unpublished observations). Therefore, co-infections by these 2 parasites are likely in natural populations of Daphnia.…”

Parasites of zooplankton and periphyton assemblages in the littoral zone of lakes in Drawa National Park, Poland

“…This parasite appeared only in spring 2011 and reached a prevalence of 5%, which is not high considering that Nematoda accounted for 11% of organisms in the periphyton. While most of the species of Pythium are pathogenic to plants recent studies on Daphnia (Cladocera) in Europe (Wolinska et al 2009), and on Asplanchna Gosse (Rotifera) in the USA (Thomas et al 2011) and Russia (Gorbunov, Kosova 2001) have showen that the genus also includes species pathogenic to water invertebrates.…”

“…The former, together with Olpidium granulatum (kingdom: Fungi; phyllum: Chytridiomycota), was also the most common on rotifers. Mycoses of Rotifera were caused also by other fungi, namely Wolinska et al (2009) recorded four species of protosoan fungal analogues (Microsporidium group), one species of fungi and nine chromistan fungal analogues members among 14 parasites infecting Daphnia. Czeczuga et al (2000) found, in studies of parasitism of Copepoda, that the occurrence of a particular fungal and protozoan and chromistan fungal species was limited to a single season.…”

“…Chytriomyces aureus Karling (kingdom: fungi; phyllum: Chytridiomycota) and chromistan Myzocytium microsporum (Karling) Sparrow and M. zoophthorum Sparrow. Most published studies concern the occurrence of parasitic microorganisms on dead (Czeczuga et al 2000;Godlewska et al 2003) or alternatively living zoohydrobionts, though in laboratory conditions (Lass, Ebert 2006;Wolinska et al 2009). To date, however, not many in situ studies related to parasitic infections of live zooplankton and zooperiphyton.…”

“…Infected and diseased individuals are more distinctive and can be the preferred target of planktivorous fish hunting by sight (Yan and Larsson 1988). Reduction of the host by planktivorous fish may lead to decreased parasites' diversity (Duffy et al 2005;Wolinska et al 2009). …”