Morphological and molecular characterization of Antonospora scoticae n. gen., n. sp (Protozoa, Microsporidia) a parasite of the communal bee, Andrenascotica 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, u ltrastructural characteristics and the nucleotide sequence of the small sub unit ribosomal RNA coding region. The parasite is apansporoblastic and deve lops 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 staine d for TEM measure 5.0 x 1.8 mu m. The exospore is four-layered, with an int ernal single layer followed by a thicker, more electron dense layer, then a nother single layer followed by a thin external double layer. The polar fil ament 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 lon g. Its GC content (62%) is significantly higher than previously reported fo r this group of organisms. The systematic position of the described microsp oridium was found to be ambiguous and is discussed in the context of incons istencies between the molecular and morphological taxonomy of microsporidia . A new genus is proposed for A. scoticae without defining superior taxa be cause the current developmental and morphological evidence is limited and p artly contradictory to the molecular data. Current taxonomies of microspori dia are based on characters that are most likely polyphyletic in nature. Tr aditional systems of microsporidian taxonomy may need to be extensively rev ised, as molecular data become available.