Inter-relationships of haplosporidians deduced from ultrastructural studies

Abstract

We reviewed papers reporting haplosporidian ultrastructure to compare inter-relationships based on ultrastructure with those based on molecular data, to identify features that may be important in haplosporidian taxonomy, and to consider parasite taxonomy in relation to host taxonomy. There were links between the following: (1) the plasmodia of an abalone parasite, Haplosporidium nelsoni and Urosporidium crescens in the release of haplosporosomes; (2) H. costale and H. armoricanum in haplosporosome shape and presence and shape of Golgi in spores; (3) basal asporous crustacean haplosporidians which form haplosporosomes from formative bodies (FBs) in vegetative stages -H. nelsoni, which forms haplosporosomes from FBs in plasmodial cytoplasm, and H. louisiana, Minchinia spp. and Bonamia perspora, which form haplosporosomes from FBs in spores; (4) crustacean haplosporidians, Bonamia spp. and M. occulta in the predominance of uni-and binucleate stages; and (5) lipid-like vesicles in sporoplasms of H. costale, H. armoricanum, H. lusitanicum, H. pickfordi, H. montforti, and B. perspora. In general, these relationships reflect phylogenies based on molecular studies. As well as spore form and ornamentation, haplosporogenesis in spores appears to be taxonomically important. Parasite and host taxonomy were linked in the infection of lower invertebrates by Urosporidium spp., the infection of oysters by Bonamia spp., and of molluscs by Minchinia spp. Haplosporidium spp. are patently an artificial, paraphyletic group probably comprising many taxa. Consequently, the taxonomy of haplosporidians needs a thorough revision.

Haplosporidium littoralis sp. nov.: a crustacean pathogen within the Haplosporida (Cercozoa, Ascetosporea)

“…Spore-forming haplosporidians of crustaceans have been described infecting the decapod Rhithro panopeus harrisii tridentatus (Marchand & Sprague 1979) and re cently from freshwater amphipods of the genus Diporeia (Messick 2009). In the recent review by Hine et al (2009), comparison of morphological and molecular features of pathogens reported in the literature as haplosporidians tentatively placed the apparently asporous group in a basal position within the taxon. It should be noted, however, that the asporous characteristic may simply reflect an as-yet undiscovered spore stage in these hosts, or alternatively, their role as an intermediate host to a definitive host in which the spore is formed (Stentiford et al 2004).…”

“…Although Perkins (2000Perkins ( , p. 1332 described the Ha plo sporida as 'parasitic protists that form ovoid, walled spores with an orifice covered externally by a hinged lid or internally by a flap of wall material', further assessment of morphological variants plus the addition of molecular phylogenetic analyses have supported inclusion of the apparently non-spore forming genus Bonamia within the Haplosporida (Carnegie et al 2000, Hine et al 2009), a placement that was confirmed with the recent description of the conventionally spore-forming species B. perspora (Carnegie et al 2006). By identifying Bonamia too as a spore-forming genus, even though B. ostreae and B. exitiosa have never been observed to form spores, the discovery of B. perspora underscored the fact that pathological assessment of limited numbers of hosts may only provide a partial view on actual life stages present within a given host species.…”

“…In addition to the formation of spores, the presence of haplosporosomes appears to be a common feature of members of Haplosporida, though once again, these may only appear in the spore stages of certain species. They may therefore remain enigmatic in those members for which these sexual stages have not been described (Hine et al 2009). Within the group, the genus Haplosporidium is the largest, containing 23 named species and 3 tentative placements (Hine et al 2009).…”

“…They may therefore remain enigmatic in those members for which these sexual stages have not been described (Hine et al 2009). Within the group, the genus Haplosporidium is the largest, containing 23 named species and 3 tentative placements (Hine et al 2009). However, molecular phylogenetics reveals this genus to be paraphyletic , likely representing an artificial grouping of numerous taxa.…”

“…Several apparently asporous haplosporidian-like pathogens have also been described infecting crustacean hosts, including blue crabs Callinectes sapidus from the USA (Newman et al 1976); spot prawns (Pandalus spp.) from the coasts of Alaska and western Canada (Meyers et al 1994, Bower & Meyer 2002, Hine et al 2009); European shore crabs Carcinus maenas from British waters (Stentiford et al 2004); and farmed Litopenaeus vannamei from Central America and Asia (Dyková et al 1988, Nunan et al 2007, Utari et al 2012. Spore-forming haplosporidians of crustaceans have been described infecting the decapod Rhithro panopeus harrisii tridentatus (Marchand & Sprague 1979) and re cently from freshwater amphipods of the genus Diporeia (Messick 2009).…”