Flabelliforma montana (Phylum Microsporidia) from Phlebotomus ariasi (Diptera, Psychodidae): ultrastructural observations and phylogenetic relationships

Abstract

Summary Ultrastructural observations are presented on Flabelliforma montana (type species) (Phylum Microsporidia) from sandflies Phlebotomus ariasi (Diptera, Psychodidae). All stages have isolated nuclei. The sporophorous vesicle (SV) arises by separation of a 5 nm layer, via small blisters, from the 15 nm surface membrane of sporonts. Sporoblasts form by deep invagination of the sporont surface, the SV at first folding inwards around the invaginations but later unfolding to form a rounded vesicle enclosing spores. The vesicle contains tubules with bulbous terminal expansions. Spores have a deeply domed anchoring disc within a polar sac which covers the anterior polaroplast, consisting of membranes acutely angled to the longitudinal axis around the straight section of the polar tube. Posterior polaroplast membranes, in the region where the polar tube changes course towards the periphery, appear almost transverse in sagittal section. The 130 nm thick endospore is overlain by several membrane-like layers, which together with amorphous material constitute the exospore. There are 3.5–4.0 coils of the polar tube. Flabelliforma ostracodae , Flabelliforma diaptomi and Flabelliforma magnivora conform well in morphology with the type species. However, when F. magnivora was included in parsimony and maximum likelihood analyses, using 16S rDNA sequences of 20 microsporidia, it emerged as unrelated to F. montana . Disparities were found between morphological characters and molecular groupings of several of the microsporidia investigated. Within clades, nuclei could be isolated or diplokaryotic, sporophorous vesicles present or absent and life cycles simple or complex.