Sex, snowballs, and the single cell: quantum evolution in cell biology and its global impact

Friday Seminar

By Thomas Cavalier-Smith.

Abstract

 

Evolution of novel body plans and adaptive zones is always by quantum evolution: exceptionally rapid concerted innovations in many body parts. I shall discuss the two most dramatic examples of quantum evolution in the history of life: the neomuran revolution and the origin of eukaryotes and sex, both dominated by intracellular coevolution. Eukaryotes and archaebacteria are phylogenetically sisters, collectively called neomura to contrast them with the more primitive eubacteria that have murein peptidoglycan walls. Their common ancestor arose from an actinobacterium during the neomuran revolution, probably only ~0.9 Gy ago, by profound alterations in the cell envelope in the most radical quantum evolution ever in bacteria. N-linked surface glycoproteins replaced murein peptidoglycan and lipoproteins, with substantial coadaptive changes in ribosomes and signal recognition particles; simultaneously, core histones evolved, stimulating marked modifications of DNA-handling enzymes. The resulting ancestral neomuran diverged rapidly to produce hyperthermophilic archaebacteria, by evolving novel acid/heat-resistant flagella and isoprenoid ether lipids, and the first eukaryotes, by evolving phagotrophy, endoskeleton, endomembrane system, novel molecular motors, nuclear pore complexes, mitosis, cyclins, sex, mitochondria (by Ą-proteobacterial enslavement), peroxisomes, centrioles and cilia. Recent advances in cell biology help explain all these eukaryotic innovations as natural coevolutionary consequences of the origin of phagotrophy, the adaptive zone of protozoa and animals. Eukaryotes were ancestrally aerobic, with a primary bifurcation between unikonts (animals, fungi, Choanozoa, Amoebozoa) and bikonts (plants, chromalveolates, excavates, Rhizaria). The origin of methanogenic archaebacteria may have indirectly caused the Neoproterozoic snowball-earth episodes of global freezing soon after eukaryotes evolved. Cyanobacterial enslavement by an early bikont probably created chloroplasts before the snowball, whereas red-algal enslavement to yield chromalveolates, and most other early eukaryote diversification, probably rapidly followed its melting.

Other information

The seminar is part of a Mini-symposium on "Evolution of prokaryotic and eukaryotic cells and phylogenetic relationships among supergroups".

The CEES seminar room has a coffee-machine – it is therefore recommended that you come a bit earlier and get yourself a good cup of coffee (for the price of 3 NOK).

 

 

Published Feb. 6, 2012 1:37 PM