Primary endosymbiosis happens when one microbial organism engulfs another. It then begins to use the swallowed organisms as an internal organ. The host provides the organism–now called an endosymbiont–several benefits including nutrients, energy, and protection. When it can no longer survive on its own, the engulfed endosymbiont becomes an organ for the host called an organelle.
“It’s very rare that organelles arise from these types of things,” Tyler Coale, a co-author of the Cell study and a postdoctoral scholar at the University of California, Santa Cruz said in a statement. “The first time we think it happened, it gave rise to all complex life.”
Endosymbiosis where the host life form becomes fundamental to another organism’s function has only happened three known times. All of these instances were a major breakthroughs for evolution, since merging with their hosts became fundamental for the endosymbionts very existence.
Can this be regarded as empirical evidence of how life developed?
I am not a scientist, so I do not know when you really can call something empirical. We were not there when it first happened. But whatever the case, this new evidence seems to aid our understanding of how things have evolved quite a lot.
This incredibly rare event occurred between a type of abundant marine algae and a bacterium was observed in a lab setting. For perspective, plants first began to dot our planet the last time this happened.
When God planted the Garden of Eden?
Gen 2:23 And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man. 24Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
It’s evidence of how life may have developed. It definitely doesn’t tell us anything about how life started.
I just had this mental image of God getting the attention of the angels and saying, “Wait for it . . . . There! Complex life begins!” and an angel says, “But that big one just ate that little one…!”
Empirical means objectively measured. For example, measuring the mass of a rock is empirical.
Empirical evidence is a set of measurements that can be used to test a hypothesis. The difference between data and evidence is how the empirical measurements interact with theories and hypotheses.
In the case under question, the empirical data is the similarity between the genetics of the endosymbiont in this species of amoeba and free-living cyanobacteria (and there is probably more evidence than this one example). This is part of the evidence for their conclusion that 120 million years ago the modern amoeba’s ancestor engulfed a cyanobacteria that went on to evolve a symbiotic relationship with the host amoeba.
The reason that it helps us to understand how chloroplasts and mitochondria evolved is that this example happened much more recently. The proposed events that led to the evolution of mitochondria and chloroplasts happened billions of years ago, so the evidence for the precise events early in that process have been lost to time. This new example happened 1/10th as long ago (120 million years ago), so it can hold clues as to how the early evolution of these endosymbiotic relationships can evolve.
Actually, there are several additional examples of such endosymbiosis in which a photosynthetic alga was incorporated into a different protist host. Those are secondary endosymbiosis; not all of the popular accounts distinguish primary endosymbiosis and secondary endosymbiosis.
Note that the 100 million years ago is based on speculation that this may have developed in response to conditions in the Cretaceous or at the K/T boundary, not on evidence.
I wonder at what point the absorbed organism becomes encoded in the host’s DNA, if it ever does. Or maybe these kinds of occurrences require a parent host organism to share material in the sex cells in some other way?
It may or may not, but chances are high over long time periods in my estimation. It requires a gene to be inserted into the host DNA along with sequence upstream to drive the expression of the inserted gene. From there, it’s a race against time as to which entity, endosymbiont or host, accumulates mutations in the gene first, doing away with its function.
It is worth mentioning that eukaryote genomes (including humans) are littered with insertions from mitochondrial DNA.
In fact, these are often used for determining evolutionary relationships, much like endogenous retroviruses.
I wonder how that works in exotic cases of parasitism like the one that infects rats but needs to incubate the next generation in a cat so it causes the rats to show themselves so the cats can eat them.
It’s like it doesn’t need to completely take over the rat organism just derange it as needed to keep itself going. But then I don’t think that require any DNA uptake?
That’s my understanding as well. Toxoplasma gondii is a protozoan that causes rats to be easier prey for cats.
According to Wiki, demethylation of rat DNA in neurons may be involved, but no uptake of T. gondii DNA into the host genome. DNA demethylation would be the result of host reactions to the presence of the parasite and whatever it may produce in the host, not direct actions of the parasite itself on the host genome.
We might mention that congenital infections with Toxoplasma (often traced to cat boxes in the US) is a major problem with sometimes severe neurologic damage in affected infants.
I tend to think of it as “nature does it because it can”. I don’t think it would be accurate to say that nature finds every possible way because many processes are contingent on their history. For example, tetrapods have 4 limbs because our lobe finned fish ancestors were able to use 4 of their fins for supporting their weight. Our arthropod cousins took many different routes, from six legs to hundreds, because of where they started their journey onto land. Contingency is one of the cooler aspects of biology and evolution, IMHO.
What isn’t possible isn’t a way as I was thinking of it. But I think we’re in agreement. Sometimes you hear people say nature is “wasteful” but I prefer “abundant”.
I like “profligate”: nature “tries” all sorts of things, some don’t work out well. “Profligate” has the idea that nature is generous with a large store of wealth.