Tuesday, April 18, 2017

Evolution of the eukaryote with OET and the endosymbiosis hypothesis

I will here describe briefly most of the evolution of eukaryotes, from the simplest cellular life form to sexually reproducing cellular units with a lot of different organelles. Evolution of introns is described elsewhere. Also the special evolution that gave rise to bacteria as separate forms of life is described in separate posts (Ref. to be added). How the evolution of eukaryotes resulted in anaerobic and aerobic forms is also treated separately. The separation of the eukaryote into two main compartments, the nucleus and the cytosol, is however treated here.

With OET all the eukaryotic features, such as organelles and sex, were created successively from the start of life in the simplest form. This simplest form was not a bacterium, as the endosymbiosis hypothesis holds. Neither archaebacteria, nor eubacteria existed at the time. The first cells originated in the RNA world, and they were quite similar to the nucleus of modern cells. In the RNA world, catalysis was controlled by ribozymes, not enzymes built from proteins. Genetics were primary also built on RNA, but DNA came into use for long term storage, much as we see it today. With the invention of translation, which was, and also today mostly is, built on RNA structures, separation into two compartments was a benefit. Special channels in the outer membrane were created. Bubbles were "blown" from these, and eventually all the bubbles united into the cytosol. With this separation the control system was well protected, and it was possible to use simple single membranous organelles. They were used to import and export metabolites from the environment. Later, also double membrane organelles were created. Viruses were created as a way to transport genetic material to other organisms, and commuting organelles were created to transport whole systems between organisms. As these could be autonomous, they could however also be used by just commuting to the environments. They became the bacteria, as described elsewhere.

With the endosymbiosis hypothesis the simplest eukaryote cell was not the nucleus, but a bacterium. Very often an archeabacterium is used as the source for the eukaryote in the various forms of endosymbiosis theories. The various forms of the hypothesis, described respectively by Lynn Margulis, Tom Cavalier-Smith and Martin & Müller propose different states of evolution of the host that received the bacterium that became the mitochondrion. But common to all of them is that evolution had a boost following this event. Features like sex and a series of organelles were invented after this event, mainly in the toxic world. In OET all these basic concepts were invented in the anoxic world, long before any bacteria existed.

The separation of the eukaryote into a nucleus and the cytosol has not been given any good explanation in the endosymbiosis hypotheses. Margulis saw the nucleus as just another organelle, and assumed that it was also the result of some endosymbiosis event. Martin & Müller may have a better explanation, but they are all quite speculative.

Why are there anaerobic eukaryotes?

Margulis described eukaryotes as aerobic organisms thriving under toxic conditions. And bacteria, that are mostly anaerobic, were by her given the honor of creating an advanced aerobic form, the eukaryote. But there are also anaerobic eukaryotes. These are with the endosymbiosis hypothesis posited to have been reverse evolved by loosing all the features that were needed for aerobic respiration, and instead new features for use under anoxic conditions were constructed. The results of this evolution were organelles like the hydrogenosomes and the mitosomes.

With OET these organelles were created at an early stage of evolution. The mitochondrion and the chloroplast represents the terminal stage of evolution, not any start of reverse evolution. OET holds that anaerobic eukaryotes are ancient, not recent forms. And that is also consistent with the phylogenetic studies that have been performed, if they are interpreted correctly.

With the endosymbiosis hypothesis we could wonder why there are anaerobic eukaryotes at all. But people, when they have been used to the endosymbiosis hypothesis, are also used to events that are almost impossible. The prevailing conditions any place where there is light is the oxic condition. And light is needed for energy generation. The anaerobic eukaryotes are therefore found only where there is no access for oxygen and where thee is a constant supply of metabolites. Typical places are in the ground and in the stomach of cows and termites. They must be older than the animals, so they must have thrived in the ground.  With OET they have remained where oxygen has not got access. With the endosymbiosis hypothesis they must have had a lot of problems moving from oxic conditions to anoxic while their metabolism has been reduced and then reinvented in another direction, a direction that was based on cooperation with certain methanogen archaebacteria. And in these habitats they would have to compete with bacteria, that were well established.