Flagellates, often treated as a uniform group, are actually among the most phylogenetically and functionally diverse eukaryotes. We are exploring this overlooked functional diversity.
Phagotrophic flagellates are found in all the major branches of the eukaryotic tree of life, and they are thus the phylogenetically most diverse group of eukaryotes.
The archetypical flagellate, characterized as a cell pushed forward by a waving flagellum, hardly exists among free-living flagellates, yet the fluid mechanics of its propulsion is intensely studied (sperm cells). In addition to propulsion, maybe the primary role of the flagella in free-living flagellates is for resource acquisition, which is little studied.
The number of flagella, their position and beat patterns, whether they are naked or equipped with hairs or vanes, varies tremendously and has obvious implications to the functioning of the flagellum for propulsion and foraging (generation of feeding current).
We are exploring this functional diversity, aiming at mechanistically understanding the diverse roles of flagella. We use high-speed video-microcopy to observe behaviors, and fluid mechanics models to understand mechanisms. Our recent work has been reviewed here
Schematic illustrating some of the morphological and functional diversity of flagellates and flagella. Flagella can be equipped with rigid hairs (red), with vanes (yellow), or they can be naked. From Kiørboe et al 2025
The flagella of a dominating group of flagellates are equipped with rigid hairs. When beating in a plane the hairs are oriented in the beat plane, and the densely spaced hairs function as a flexible sheet that spread out on at one side of the crest, and come together on the other, thus creating an area anisotropi that generates a net for towards the cell (A). Thus, the presence of hairs reverses the force direction. Some species wind up their flagellum in 3D while foraging (B), and the consequent torsion of the flagellum dictates the orientation of the hairs. To generate a feeding current towards the cell, as observed, the flagellum must dynamically twist + 600 around its own axis at 50 Hz. From Kiørboe et al 2025