tag:blogger.com,1999:blog-8165796739811288266.post160458188354928319..comments2023-09-05T14:15:42.517+03:00Comments on Phylogenetics...: Root of the Eukaryotic Tree of LifeAnonymoushttp://www.blogger.com/profile/18030008254403295490noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-8165796739811288266.post-12777569362757034402017-02-20T22:21:01.326+02:002017-02-20T22:21:01.326+02:00Hi Alex,
I'll answer the second question firs...Hi Alex,<br /><br />I'll answer the second question first.<br /><br />2. Genetic (phylogenies of universal genes) and cellular data (e.g. presence of nucleus, mitochondria, Golgi apparatus etc. and details of these structures) clearly suggest that eukaryotes have single origin. 50-60 years ago when most of that data was missing, it was seriously considered that eukaryotes might be polyphyletic, that different groups might have originated from different prokaryotes. Today there is no evidence for that. Although eukaryote specific cellular structures suggest monophyly (single origin) of this group, they do not really pinpoint from which prokaryotic group eukaryotes evolved, because there almost are no comparable structures in prokaryotes. Phylogenies estimated from universal genes (mainly transcription and translation related) clearly show eukaryote monophyly and their origin from Archaea. Phylogenies estimated from mitochondrial genes also support eukaryote mononphyly (all eukaryotes had or have had mitochondria) and their origin from Alphaproteobacteria. In these gene trees all eukaryotes are very closely related (protein sequences of some of these genes are hardly different between animals and plants for example) compared to the diversity within prokaryotes. Specific similarities with certain prokaryotes in some eukaryotes (e.g. plastids from cyanobacteria and horizontally transferred single genes) are all later acquisitions after eukaryotes already had nucleus, mitochondria etc. Anyway, I think no researcher nowadays seriously suggests that eukaryotes evolved multiple times from prokaryotes.<br /><br />1. Considering the monophyly of eukaryotes, it is parsimonious to assume that last eukaryotic common ancestor (LECA) had the characters that all eukaryotes now have. There are no good reasons to suggest in case of monophyly that nucleus etc. evolved independently in different eukaryotes. First eukaryotic common ancestor (FECA) is a different thing. If eukaryotes originated in a merger of Archaea and Bacteria, then FECA would be a bacterium (ancestor of mitochondrion) inside an archaeon without any eukaryote specific characters (this scenario seems most likely to me in light of recent literature). Or if some prokaryote gradually evolved to become eukaryote and only later picked up mitochondrion, then FECA would simply be some kind of prokaryote.<br /><br />Hope it helped.<br /><br />For example Nick Lane has written about these things in his recent book "The Vital Question". Worth reading, not just because of interesting topics, but also because he is a good writer.Anonymoushttps://www.blogger.com/profile/18030008254403295490noreply@blogger.comtag:blogger.com,1999:blog-8165796739811288266.post-75846012128381273562017-02-20T02:43:01.418+02:002017-02-20T02:43:01.418+02:00Nice post, Marko. Great summary of the current sta...Nice post, Marko. Great summary of the current state of the LECA. Could you help me understand a few things? <br /><br />1. Why is the LECA thought to be a protist when it would most likely be more similar to lokiarchaeota or another archaeon? If the latter is true, then shouldn't the LECA be talked about as a nucleated archaeon rather than a protist similar to Malawimonas?<br /><br />2. What are the data suggesting eukaryotes share one common ancestor and not many (like bacteria)? Is it not a more plausible scenario that multiple nucleated archaea gave rise to various eukaryotic lineages which are represented in the different supergroups? Is there evidence against this scenario?<br /><br />If you happen to find the time to read and reply - thanks so much!Anonymoushttps://www.blogger.com/profile/00324857028869481980noreply@blogger.com