Phylogenetic analysis of phagotrophic, photomorphic and osmotrophic euglenoids by using the nuclear 18S rDNA sequence.

Abstract

Phylogenetic analyses of 35 strains including 25 previously published sequences and 10 which have been newly sequenced, representing two species of Euglena, five species of Phacus and three species of Astasia, were carried out using the SSU rDNA. Parsimony, distance and maximum-likelihood inferred phylogenies support (1) monophyly of the euglenoids, (2) kinetoplastids as the sister group, (3) the phagotrophic Petalomonas cantuscygni Cann et Pennick anchoring the base of the euglenoid lineage, (4) evolution of phototrophy within the euglenoids from a single event, (5) multiple origins of osmotrophic euglenoids and (6) polyphyly of the genera Euglena Ehrenberg and Phacus Dujardin. Analyses also indicate that Lepocinclis Perty, Trachelomonas Ehrenberg and Astasia Dujardin are polyphyletic. In addition, the results suggest that neither the Euglenales nor the Eutreptiales form a monophyletic lineage, thus questioning currently available classifications. Concerning the phagotrophic mode of nutrition, the data suggest that the feeding apparatus arose multiple times.

Character evolution in heterotrophic euglenids

“…However, this union of character states begs the question: Is P. cantuscygni more closely related to euglenids or kinetoplastids? Phylogenetic analyses of small subunit rDNA using non-euglenozoan outgroups incontrovertibly demonstrate that P. cantuscygni forms the sister taxon to the other euglenids in the ingroup (Müllner et al 2001;Preisfeld et al 2000Preisfeld et al , 2001. We can infer from these data that the Euglenida was derived from an ancestor possessing kinetoplasts and, consequently, the Kinetoplastida is paraphyletic.…”

“…The idea that Distigma, Eutreptia, and Eutreptiella should be classified together within an order "Eutreptiales" is inconsistent with both molecular and morphological data (Müllner et al 2001;Preisfeld et al 2001) (Fig. 14).…”

“…comma and A. curvata, Müllner et al 2001). If these taxa are truly misplaced as small subunit rDNA sequences suggest (Müllner et al 2001), then they provide additional intermediate states between the biflagellated distigmids and the uniflagellated rhabdomonads. Detailed analyses of the pellicle of these "Astasia" taxa, particularly the value of P (the number of strip around the cell periphery) and W P (the number of whorls of strip reduction), will more confidently demonstrate their relationship to distigmids (Angeler 1998;Angeler et al 1999;Leander and Farmer 2000a); distigmids possess P = 18-20 and W P = 0, whereas Astasia (e.g., A. longa) possesses P = 40 and W P = 3 (Leander and Farmer 2000a).…”

“…Arrows indicate homologous heel-like structures marking the articulation zones between fused strips. sistent with the finding of Müllner et al (2001) and Preisfeld et al (2001) using small subunit rDNA sequences. Clade I was rather surprisingly derived from within the eukaryotrophs (Fig.…”

“…motrophs like distigmids and rhabdomonads (Fig. 1d-e) is less obvious; however, small subunit (18S) rDNA sequences indicate that they diverged prior to the eukaryotrophic Peranema and the phototrophs (Preisfeld et al 2000(Preisfeld et al , 2001Leander and Farmer 2001b;Müllner et al 2001). We are interested in identifying the key morphological innovations in euglenid evolution associated with the transitions between bacteriotrophy, eukaryotrophy, phototrophy, and osmotrophy, but it is first necessary to establish a robust phylogenetic hypothesis for euglenids as a whole.…”