PHYLOGENY OF PHAGOTROPHIC EUGLENIDS (EUGLENOZOA): A MOLECULAR APPROACH BASED ON CULTURE MATERIAL AND ENVIRONMENTAL SAMPLES¹

Abstract

Molecular studies based on small subunit (SSU) rDNA sequences addressing euglenid phylogeny hitherto suffered from the lack of available data about phagotrophic species. To extend the taxon sampling, SSU rRNA genes from species of seven genera of phagotrophic euglenids were investigated. Sequence analyses revealed an increasing genetic diversity among euglenid SSU rDNA sequences compared with other well‐known eukaryotic groups, reflecting an equally broad diversity of morphological characters among euglenid phagotrophs. Phylogenetic inference using standard parsimony and likelihood approaches as well as Bayesian inference and spectral analyses revealed no clear support for euglenid monophyly. Among phagotrophs, monophyly of Petalomonas cantuscygni and Notosolenus ostium, both comprising simple ingestion apparatuses, is strongly supported. A moderately supported clade comprises phototrophic euglenids and primary osmotrophic euglenids together with phagotrophs, exhibiting a primarily flexible pellicle composed of numerous helically arranged strips and a complex ingestion apparatus with two supporting rods and four curved vanes. Comparison of molecular and morphological data is used to demonstrate the difficulties to formulate a hypothesis about how the ingestion apparatus evolved in this group.

Ribosomal RNA Phylogeny of Bodonid and Diplonemid Flagellates and the Evolution of Euglenozoa

“…Peranemida have a type III apparatus (curved vanes, 2 rods with internal microtubules). The position of Dinema was not resolved previously (Busse, Patterson, and Preisfeld 2003), but we have shown that it groups with Anisonema and Peranema sp. with 96–99% support.…”

“…2 largely bacteriotrophic Petalomonadida are the earliest diverging euglenoids. Except for the robust sister relationship between Euglenida and Eutreptiida (previously found by Brosnan et al 2003; Marin et al 2003; and Busse, Patterson, and Preisfeld 2003), the branching order of the six euglenoid orders is poorly resolved, suggesting rapid early radiation among the phagotrophs and/or near mutational saturation.…”

“…The significantly deeper branching of the phagotrophic taxa is also poorly resolved. As Busse, Patterson, and Preisfeld (2003) pointed out, neither ultrastructure nor molecular evidence supports their traditional separation into two suborders, Sphenomonadina and Heteronematina (Leedale 1967). Instead our Fig.…”

“…Plicostoma (Cavalier‐Smith 1998). Additionally, analyses are hampered by divergent evolutionary rates of the 18S rRNA genes of these groups (Busse and Preisfeld 2002b; Busse, Patterson, and Preisfeld 2003). Resolving the earliest relationships within Euglenozoa is also impeded by mutational near‐saturation of euglenoid 18S rRNA (Moreira, Lopez‐Garcfa, and Rodriguez‐Valera 2001).…”

Morphological and Molecular Characterisation of Notosolenus urceolatus Larsen and Patterson 1990, a Member of an Understudied Deep‐branching Euglenid Group (Petalomonads)

“…Later 18S rDNA analyses with increased representation of phagotrophic euglenids typically provided little‐to‐no support for a basal position of petalomonads (Busse et al. ; von der Heyden et al. ).…”