Eukaryovorous Predation in Evolutionarily Significant Excavate-Like Flagellates

Accumulating evidence suggests that the Last Eukaryotic Common Ancestor (LECA) resembled contemporary excavates, a non-monophyletic group of deep branching flagellates. Here we explore the functional ecology of distantly related deep-branching "excavate-like" flagellates (in Alveolata and Provora) that share with many excavates a vane-bearing posterior flagellum beating in association with a ventral groove. This arrangement is key to generating a feeding current in the bacterivorous typical excavates. However, the four species examined here are motile "hunters" that randomly encounter eukaryotic prey. Initial prey attachment may be facilitated by the force generated by the vaned flagellum but eventually by firing extrusomes. Propulsion is driven by the two flagella that are directed backwards. Despite minor differences, the propulsion and hunting strategies are similar between these two deep-branching groups and distinctly different from those found in typical excavates. While the vane-and-groove morphology may help prey attachment, simulations show that it seems energetically disadvantageous to propulsion. Thus, its overall role, origin, and phylogenetic implications remain unclear. This study adds to our knowledge of the functional ecological range of living vane- and groove-bearing flagellates. Given their significance to understanding early eukaryote evolutionary history, this may in turn shed light on the deep history of eukaryote life.