Reconciling morphological and molecular classification of predatory ciliates: Evolutionary taxonomy of dileptids (Ciliophora, Litostomatea, Rhynchostomatia)

Abstract

The order Dileptida is a small group of predatory ciliates characterized by a proboscis serving for prey capture. Although monophyly of the order is strongly supported, generic relationships between dileptid taxa were left mostly unresolved in 18S rRNA gene phylogenies. To overcome this problem, we applied the synergistic effect of combining multiple molecular markers with morphological data. Furthermore, we inferred dileptid evolutionary history by a multifaceted analysis strategy, including tree-building methods, phylogenetic networks, split spectrum analysis, quartet likelihood mapping, and reconstruction of ancestral morphologies. This complex approach revealed: (1) monophyly of the families Dimacrocaryonidae and Dileptidae; (2) polyphyly of Microdileptus, Pseudomonilicaryon, and Rimaleptus; and (3) homoplastic nature of several generic diagnostic features, viz., macronuclear pattern, size of oral bulge opening, and orientation of preoral kineties. Controversies in the internal phylogeny of the family Dimacrocaryonidae could be elucidated after reconstruction of ancestral morphologies at deeper nodes of phylogenetic trees in a combination with budding evolutionary processes. Moreover, we solved the “Rimaleptus” dilemma by splitting the family Dimacrocaryonidae into two new subfamilies, the Dimacrocaryoninae with two-rowed dorsal brush and the Rimaleptinae with multi-rowed brush as well as by establishing a new genus, Rurikoplites, from whose species several dimacrocaryonid genera very likely evolved by budding.