Multiple losses of sex within a single genus of Microsporidia

Abstract

Background: Most asexual eukaryotic lineages have arisen recently from sexual ancestors and contain few ecologically distinct species, providing evidence for long-term advantages of sex. Ancient asexual lineages provide rare exceptions to this rule and so can yield valuable information relating to the evolutionary forces underlying the maintenance of sex. Microsporidia are parasitic, unicellular fungi. They include many asexual species which have traditionally been grouped together into large, presumably ancient taxonomic groups. However, these putative ancient asexual lineages have been identified on the basis of morphology, life cycles and small subunit ribosomal RNA (16S rRNA) gene sequences, all of which hold questionable value in accurately inferring phylogenetic relationships among microsporidia.

Phylogenetic characterization of a microsporidium (Endoreticulatus sp. Zhenjiang) isolated from the silkworm, Bombyx mori

“…Additionally, the arrangement of rRNA genes has recently become an important parameter for identifying microsporidia. Tsai et al (2005) have suggested that the reversed arrangement of rRNA genes as LSU-SSU-5S arrangement may be a specific characteristic for identifying Nosema species (Huang et al 2004;Ironside 2007;Tsai et al 2005).…”

Morphological and molecular studies of a microsporidium (Nosema sp.) isolated from the thee spot grass yellow butterfly, Eurema blanda arsakia (Lepidoptera: Pieridae)

“…Additionally, the arrangement of rRNA genes has recently become another important parameter for identifying microsporidia. The large subunit (LSU)-small subunit (SSU)-5S arrangement of rRNA genes, for example, is a character that appears to be specific to the genus Nosema (Huang et al, 2004;Tsai et al, 2005;Ironside, 2007).…”

Reduction in the sex ability of worldwide clonal populations of Puccinia striiformis f.sp. tritici

“…Moreover, in a given species, populations from different geographical areas may diverge with respect to their reproductive cycle (Barrett et al, 2008;Burdon and Roelfs, 1985;Groth and Roelfs, 1982). In order to explain this variability in the mode of reproduction, an issue related to the evolution of sex in a species (McDonald and Linde, 2002;Michod et al, 2008), different hypothesis have been put forward and have mainly focused on the long term vs. short term adaptive advantages of sex, the resistance of sexual spores to adverse environments (Anikster, 1986;Barrett et al, 2008) and the use of alternate hosts that may be available at appropriate times (Ironside, 2007). Knowledge of the identity of species and populations and their reproductive modes, while adopting a broad view of pathogen behaviour in space and time, should improve the abilities of pathologists for better disease management and even predict pathogen behaviour (Taylor et al, 1999).…”