Morphological and molecular characterization of Antonospora scoticae n. gen., n. sp. (Protozoa, Microsporidia) a parasite of the communal bee, Andrena scotica Perkins, 1916 (Hymenoptera, Andrenidae

The new microsporidium Antonospora scoticae n. gen., n. sp., a parasite of the communal bee Andrena scotica, is described based on light microscopy, ultrastructural characteristics and the nucleotide sequence of the small subunit ribosomal RNA coding region. The parasite is apansporoblastic and develops in close contact with the host cytoplasm. All developmental stages are diplokaryotic. Cytoplasmic fission was not observed, but the sporogony is believed to be disporoblastic. Live spores are ovocylindrical, straight to slightly curved, and measure 6.8 x 2.7 mu m whereas spores fixed and stained for TEM measure 5.0 x 1.8 mu m. The exospore is four-layered, with an internal single layer followed by a thicker, more electron dense layer, then another single layer followed by a thin external double layer. The polar filament is isofilar and arranged in 15-22 coils in the posterior and mid-part of the spore. The polaroplast has tightly packed lamellae that become less densely packed in the posterior region. The coding region of the small subunit ribosomal RNA is 1371 base pairs long. Its GC content (62%) is significantly higher than previously reported for this group of organisms. The systematic position of the described microsporidium was found to be ambiguous and is discussed in the context of inconsistencies between the molecular and morphological taxonomy of microsporidia. A new genus is proposed for A. scoticae without defining superior taxa because the current developmental and morphological evidence is limited and partly contradictory to the molecular data. Current taxonomies of microsporidia are based on characters that are most likely polyphyletic in nature. Traditional systems of microsporidian taxonomy may need to be extensively revised, as molecular data become available.