Evolutionary history of the genus Euplotes.

Phylogenetic relationships are based on recent SSU rRNA gene analyses (see also Fig 3). Colors on branches represent habitats, according to sequence metadata and literature. The 38 morphospecies included were grouped in 15 monophyletic subclades. When species within a subclade did not all share the same environment (see text), majority-rule consensus was applied. Schematic drawings represent the dorsal argyrome type(s) and frontoventral cirral pattern(s) of the species in each subclade (the argyrome type of E. dammamensis is unknown). Dimensions of the drawings correlate with the average size of the species. The character status of ancestors was inferred using a parsimony criterion. Changes in the argyrome type (green) or the number of frontoventral cirri (red) are shown on branches. Intra-subclade variability is highlighted with colored boxes: red-shaded cirri were lost and green-shaded dargyrome types were acquired by the marked species. The establishment of the obligate symbiosis between Euplotes species and the betaproteobacterium Polynucleobacter is also shown.