Molecular Phylogeny and Surface Morphology of Marine Aseptate Gregarines (Apicomplexa): Selenidium Spp. And Lecudina SPP

Abstract

Many aseptate gregarines from marine invertebrate hosts are thought to have retained several plesiomorphic characteristics and are instrumental in understanding the early evolution of intracellular parasitism in apicomplexans and the phylogenetic position of cryptosporidians. We sequenced the small-subunit (SSU) ribosomal RNA genes from 2 archigregarines, Selenidium terebellae and Selenidium vivax, and 2 morphotypes of the marine eugregarine Lecudina polymorpha. We also used scanning electron microscopy to investigate the surface morphology of trophozoites from Lecudina tuzetae, Monocystis agilis, the 2 species of Selenidium, and the 2 morphotypes of L. polymorpha. The SSU ribosomal DNA sequences from S. vivax and L. polymorpha had long branch lengths characteristic of other gregarine sequences. However, the sequence from S. terebellae was not exceptionally divergent and consistently emerged as 1 of the earliest 'true' gregarines in phylogenetic analyses. Statistical support for the sister relationship between Cryptosporidium spp. and gregarines was significantly bolstered in analyses including the sequence from S. terebellae but excluding the longest branches in the alignment. Eugregarines formed a monophyletic group with the neogregarine Ophryocystis, suggesting that trophozoites with elaborate cortex folds and gliding motility evolved only once. The trophozoites from the 2 species of Selenidium shared novel transverse striations but differed from one another in overall cell morphologies and writhing behavior.

The spermatozoon ofLumbrineris (Scoletoma) impatiens(Claparède, 1868) (Polychaeta, Lumbrineridae)

“…On the other hand, the spermatozoon of Lumbrineris sp. from Grappler Inlet, Vancouver Island (Leander et al 2003), compared with those of the species so far studied (Rouse 1988;Messina et al 2005), differs greatly in external morphology, in size of the nucleus, which is rather elongated, and in number and shape of mitochondria. These findings highlight the considerable variability of form and structure of sperm in similar polychaetes species which inhabit distant seas and oceans, as noted also by our previous studies (Conti et al 2005).…”

“…Messina et al (2005) recently demonstrated the close relationship between free-spawning and the ect-aquasperm morphology in a population of Lumbrineris (Scoletoma) impatiens (Claparède, 1868) (Lumbrineridae) from the Gulf of Naples (Italy), by in vitro experiments on fertilization and by TEM observations. Furthermore, Leander et al (2003) studied the phylogeny of Lecudina spp., a marine gregarine parasite of Lumbrineris sp. from Grappler *Correspondence: Gabriele Conti, Department of Cytomorphology, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.…”

Description of Trichotokara nothriae n. gen. et sp. (Apicomplexa, Lecudinidae) – An intestinal gregarine of Nothria conchylega (Polychaeta, Onuphidae)

“…3), the only other SSU rDNA sequences from lecudinid gregarines that possess a prominently elongated mucron (Leander et al, 2003b). Like the sequences from T. nothriae, the sequences from the two morphotypes of L. polymorpha were highly divergent relative to the other known gregarine sequences.…”

“…This genus has emerged as a ''catch-all" taxon for marine aseptate gregarines that inhabit the intestines of polychaetes (and a few other host taxa). Consequently, the actual diversity of these parasites is greatly underestimated, and the identity and composition of Lecudina has become even more ill-defined within the context of modern molecular phylogenetic and comparative ultrastructural data (Leander et al, 2003b;Leander, 2008;Rueckert and Leander, 2009).…”

“…Accordingly, the host taxon has been used as corroborating evidence for the delimitation of different gregarine species that are otherwise differentiated on the basis of molecular phylogenetic data and comparative morphology. A common morphological feature of the trophozoites of marine eugregarines is a cell cortex consisting of longitudinal epicytic folds that can vary considerably in overall number (Leander et al, 2003b;Leander, 2008). Some marine gregarines also possess conspicuous hair-like projections on the surface of the trophozoites, such as Filipodium (archigregarine), Diplauxis (eugregarine), Urospora (eugregarine) and Cochleomeritus (eugregarine).…”