Phylogenetic approaches to construct the eukaryote tree of life typically use molecular and morphological cues from contemporary flagellates. Both have issues. We propose to use ‘function’ as an additional lens.
I have recently become interested in using the function of flagella in flagellates as an additional cue to explore eukaryote evolution. The idea is to look for not only morphologies but also functions that are found in deep branches of the tree. Such form & function may represent traits that are characteristic of the Last Eukaryotic Common Ancestor (LECA).
The eukaryotic tree of life, with identification of typical excavates and excavate like groups. Insert is a schematic of excavate morphology.
One example is a group of distantly related flagellates, so-called typical excavates, that have shared morphological features (a vaned flagellum beating in a ventral groove). Molecular phylogenies suggest that they are all rooted in LECA. Do they function the same way? Despite many differences in morphological features, they indeed appear to function similarly in the context of foraging. You can see the paper on foraging mechanisms in flagellates here
Flagellates from other deep-branching groups, the ‘excavate-like’ flagellates, have similar morphologies. Do they also function the same way? If not, the excavate morphology is not the result of convergent evolution but may be an ancient trait characteristic of LECA. We are exploring this.