endosymbiont

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These are Scaly-foot snail (Chrysomallon squamiferum), an iconic vent endemic gastropod known only from the Indian ocean deep-sea hydrothermal vents, at more than 2500 metres deep.

This unique snail species lives just beside black smokers that are churning out superheated water exceeding 350°C. Has also harnessed the power of chemosynthesis, housing endosymbiotic bacteria in an enlarged part of its gut. This produces the energy it needs. it has a food factory inside its body and doesn’t even need to feed! This is likely the reason it can grow to about 45mm in size, when most of its close relatives without endosymbionts are only 15mm or smaller.

I was asked by @fortethegemini what diatoms are if they aren’t plants, and I figured I’d just make a whole post out of it since it’s a pretty complicated topic.

Here in this phylogenetic tree of eukaryotes (courtesy of Worden et al, 2015) we can see that diatoms are in the clade Stramenopiles, in the upper left. Plants, on the other hand, belong to Archaeplastida. I know those words probably don’t mean much, so to put it simply diatoms are separated from plants by about 1 billion years of evolution. That is to say, their nearest common ancestor split into two lineages 1 billion years ago, one lineage which would become the Stramenopiles, and the other archaeplastids.

Diatoms are actually closely related to brown algae (like kelp) and oomycetes (the nasty “molds” that cause the Irish Potato Famine).

So this all begs the question: how come diatoms are photosynthetic like plants, yet so far apart on the tree of life?

One thing to realize is that these trees of life don’t show you the whole picture. We need to go back in time, over a billion years ago. A eukaryotic cell once enveloped a photosynthetic cyanobacterium (the original photosynthesizers) but instead of digesting it, the cell kept the cyanobacterium around as a sort of photosynthetic livestock. Eventually, the cell line with these “livestock” would evolve and diverge and become red algae, green algae, and plants. The cyanobacteria eventually became what we know now as chloroplasts. This is called primary endosymbiosis, and it’s also how we got mitochondria.

But it gets more complicated.

(image also courtesy of Worden et al, 2015)

The ancestor of diatoms was a predatory, non-photosynthetic cell that engulfed a red algae and also kept it around instead of digesting it. This is called secondary endosymbiosis. To make things even more confusing, there’s evidence that some cells have practiced tertiary endosymbiosis, a sort of Russian doll of endosymbionts.

I know this sounds completely far-fetched, but there’s lots of evidence for the endosymbiotic theory. For starters, chloroplasts and mitochondria have their own genomes tucked away inside them, genomes that very closely resemble bacterial genomes when you get down to the molecular scale. Another piece of evidence is the extra membranes they have. Chloroplasts have an extra membrane from when the eukaryotic cell enveloped and ate it. Then, in secondary endosymbiosis, the chloroplast has three to four membranes, and in some lineages the nucleus of the algae that was eaten was retained inside what is now the newer chloroplast.

Well there you have it. Please, don’t feel hesitant to ask me any questions. I’ll be happy to clear up any concepts for anyone who is reading this!

anonymous asked:

You did not present the science against evolution at all though. The intelligent design theory is BACKED BY SCIENCE, not just certain religions. The complexities of the cell could not have arisen over time. Darwin himself said that a discovery (such as machines in the cell) would disprove him. I am not bashing your faith in proteins to spontaneously become life. I am simply presenting beliefs that were incorrectly presented. "The Bible said so" is NOT the reason I believe in intelligent design.

It happened. Finally. I knew it would. Thank you, anon, for your question.

The answer to this ask is extremely long so I have hidden it below the cut once more, to avoid the cluttering of your dashes. I apologise profusely to those of you who are mobile bloggers, and therefore do not have the luxury of the Read More button.

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