The Phylogeny of Colpodellids (Alveolata) Using Small Subunit rRNA Gene Sequences Suggests They are the Free‐living Sister Group to Apicomplexans

Abstract

In an attempt to reconstruct early alveolate evolution, we have examined the phylogenetic position of colpodellids by analyzing small subunit rDNA sequences from Colpodella pontica Myl'nikov 2000 and Colpodella sp. (American Type Culture Collection 50594). All phylogenetic analyses grouped the colpodellid sequences together with strong support and placed them strongly within the Alveolata. Most analyses showed colpodellids as the sister group to an apicomplexan clade, albeit with weak support. Sequences from two perkinsids, Perkinsus and Parvilucifera, clustered together and consistently branched as the sister group to dinoflagellates as shown previously. These data demonstrate that colpodellids and perkinsids are plesiomorphically similar in morphology and help provide a phylogenetic framework for inferring the combination of character states present in the last common ancestor of dinoflagellates and apicomplexans. We can infer that this ancestor was probably a myzocytotic predator with two heterodynamic flagella, micropores, trichocysts, rhoptries, micronemes, a polar ring, and a coiled open-sided conoid. This ancestor also very likely contained a plastid, but it is presently not certain whether it was photosynthetic, and it is not clear whether extant perkinsids or colpodellids have retained the organelle.

Prospects for elucidating the phylogeny of the Apicomplexa

“…Therefore, the characters upon which these three genera were originally based need to be re-evaluated, including the location of the tissue cysts (brain versus muscles) and the type of heteroxeny (facultative versus obligate); and both of these characters have been successfully re-evaluated. Similar re-interpretations have also occurred for the phenotypic data of other genera such as Colpodella & Perkinsus (Siddall et al, 2001;Kuvardina et al, 2002) and Cryptosporidium & Isospora (Tenter et al, 2002). For example, the ineffectiveness on Cryptosporidium of anti-coccidial agents is easily explained if it is not part of the Coccidia, as has been repeatedly shown (Barta & Thompson, 2006).…”

“…close to or within the Apicomplexa), such as: Blastocystea (0 sequence), Colpodella (6) and Metchnikovellea (0). Perhaps the only worthwhile contribution, to date, of molecular data to the base of the Apicomplexan tree is the clear exclusion of Perkinsus from the phylum (Siddall et al, 2001;Kuvardina et al, 2002;Saldarriaga et al, 2003). Basal taxa are vital for the rooting of the phylogenetic tree, which then determines the relationships among the other taxa, and thus the definition of the clades.…”

Freshwater Perkinsea and marine-freshwater colonizations revealed by pyrosequencing and phylogeny of environmental rDNA

“…The deep phylogenetic relationships within dinozoa have been difficult to resolve, particularly because of the rapid diversification and highly uneven evolutionary rates of many of the groups (Siddall et al, 2001;Kuvardina et al, 2002;Leander et al, 2003aLeander et al, , 2003bCavalier-Smith and Chao, 2004;Silberman et al, 2004;Groisillier et al, 2006;Shalchian-Tabrizi et al 2006). The increased taxon sampling of Perkinsea and application of covarion evolutionary models in this study has provided support for Perkinsea as sister to the dinoflagellates and MA.…”

Eukaryotic Flagella: Variations in Form, Function, and Composition during Evolution

“…They are thought to have evolved from free-living marine algae; among their closest extant relations are the recently discovered chromerid algae from the Australian Great Barrier Reef and the predatory colpodellids (Kuvardina et al 2002, Moore et al 2008. As with many other eukaryotic lineages some apicomplexans have secondarily lost the ability to build a flagellum, but as a group the apicomplexans owe their name to the unique, polarity-defining MTOC called the 'apical polar ring' from which sub-pellicular microtubules that define cell shape radiate.…”