The origin or rise of eukaryophagy – the predatory mode whereby eukaryotes obtain and ingest nutrients from other eukaryotes via phagocytosis – has been proposed as a major driver for eukaryotic diversification in the mid-Neoproterozoic. Evaluating this hypothesis, however, depends on first establishing the origin of a much more fundamental eukaryotic process – phagocytosis itself. Phagocytosis, or cell eating, is a eukaryote-specific process where particulate matter is engulfed via invaginations of the plasma membrane. When phagocytosis originated has been central to discussions on eukaryogenesis for decades, where phagocytosis is argued either as being a prerequisite for, or consequence of, the acquisition of the ancestral mitochondrion. In recent years, metagenomic, phylogenetic, and cytological evidence have increasingly supported the view that the pre-mitochondrial host cell – a bona fide archaeon branching within the Asgardarchaeota – was incapable of phagocytosis and used alternative mechanisms to assimilate the alphaproteobacterial ancestor of mitochondria. Indeed, the diversity and variability of proteins involved in phagocytosis across the eukaryotic tree suggest that phagocytosis may have evolved independently several times within the eukaryotic crown-group. Since phagocytosis is so essential to the functioning of modern marine food webs (without it, there would be no ‘microbial loop’ or animal life), multiple late origins of phagocytosis could help explain why many of the ecological and evolutionary innovations of the late Proterozoic (e.g. the advent of eukaryotic biomineralization, the ‘rise of algae’, and the origin of animals) happened when they did and not earlier in Earth history.
Environmental Geology & Geochemistry Seminar (EGGS) Seminar
Thu, Nov 21, 2019, 12:30 pm to 1:30 pm