title: (Cryptic) sex in the microsporidian Nosema granulosis--evidence from parasite rDNA and host mitochondrial DNA.
abstract: Microsporidia are single-celled, intracellular eukaryotes that parasitise a wide range of animals. The Nosema/Vairimorpha group includes some putative asexual species, and asexuality is proposed to have originated multiple times from sexual ancestors. Here, we studied the variation in the ribosomal DNA (rDNA) of 14 isolates of the presumed apomictic and vertically transmitted Nosema granulosis to evaluate its sexual status. The analysed DNA fragment contained a part of the small-subunit ribosomal gene (SSU) and the entire intergenic spacer (IGS). The mitochondrial cox1 gene of the host Gammarus duebeni (Crustacea) was analysed to temporally calibrate the system and to test the expectation of cophylogeny of host and parasite genealogies. Genetic variability of the SSU gene was very low within and between the isolates. In contrast, intraisolate (within a single host) variability of the IGS felt in two categories, because 12 isolates possess a very high IGS genetic diversity and two isolates were almost invariable in the IGS. This difference suggests variable models of rDNA evolution involving birth-and-death and unexpectedly concerted evolution. An alternative explanation could be a likewise unattended mixed infection of host individuals by more than one parasite strain. Despite considerable genetic divergence between associated host mitochondrial haplotypes, some N. granulosis 'IGS populations' seem not to belong to different gene pools; the relevant tests failed to show significant differences between populations. A set of recombinant IGS sequences made our data incompatible with the model of a solely maternally inherited, asexual species. In line with recent reports, our study supports the hypothesis that some assumed apomictic Microsporidia did not entirely abstain from the evolutionary advantages of sex. In addition, the presented data indicate that horizontal transmission may occur occasionally. This transmission mode could be a survival strategy of N. granulosis whose host often populates ephemeral habitats.
authors.affiliation: University of Rostock, Institute of Biological Sciences, Albert-Einstein-Strasse 3, D-18051 Rostock, Germany. Electronic address: lukaskrebes@web.de.
authors.forename: Lukas
authors.initials: L
authors.lastname: Krebes
authors.affiliation: University of Rostock, Institute of Biological Sciences, Albert-Einstein-Strasse 3, D-18051 Rostock, Germany.
authors.forename: Lisza
authors.initials: L
authors.lastname: Zeidler
authors.affiliation: University of Rostock, Institute of Biological Sciences, Albert-Einstein-Strasse 3, D-18051 Rostock, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Frankowski
authors.affiliation: University of Rostock, Institute of Biological Sciences, Albert-Einstein-Strasse 3, D-18051 Rostock, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Bastrop
mesh_terms: D033304:Amphipoda / Q000235:genetics* / Q000382:microbiology*; D000818:Animals; D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D049770:Genes, Mating Type, Fungal; D014644:Genetic Variation; D015233:Models, Statistical; D008969:Molecular Sequence Data; D016818:Nosema / Q000145:classification / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny; D011995:Recombination, Genetic
chemical_list: D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D004275:DNA, Ribosomal
keywords: Microsporidia; Mode of transmission; Nosema; Recombination; Sexual reproduction; rDNA