Santos photosynthetic molluscs Batman!
By: Lionel Perez Valenzuela
to Batman certainly would have been astonished if we had said years ago that someday find photosynthetic animals.
Certain animals in evolutionary history have adopted different strategies with regard to plants.
There are some who can blend, change color or even change shape and texture to look like a plant, which gives shelter and protection.
Others may feed of seaweed, is used as the energy source.
There are also species of nudibranchs feeding also can keep the algae cells in their bodies to blend with their surroundings. But these cells are only maintained for a short time, forcing the animal to feed it constantly. Finally
certain mollusks have gone a step further by feeding on algae, the chloroplasts of algae incorporated keeping them inside their cells for several months, using the resources that gives photosynthesis.
This is exactly what makes Elysia chlorotica, a kind of sea slug, feeding on a green alga called Vaucheria litorea .
Elysia Juveniles are reddish-brown until they begin to alimentrse the algae. Once you begin to enter the first chloroplast change color.
Figure 1. Different stages of development Elysa chlorotica. Note the lack of green pigmentation in the early stages.
When Elysa feeds algae sucks the content of chloroplasts but not destroyed, but the stores inside its own cells, digestive glands (diverticula) that branch throughout the body. Chloroplasts once inside the cells of the mollusc is alive and functioning (ie by photosynthesis) for up to 9-10 months.
Figure 2. If we deprive Elysa chlorotica for several months the algae chloroplasts remain functional, as evidenced by intact membranes observed by electron microscopy (transmission electron microscope), even if loss of green color. Photos AD: intact chloroplasts in algae. Photos BE: chloroplasts in the animal deprived of algae for two months. CF Photos: Animals deprived of seaweed for eight months. The chloroplasts found within animal cell.
During that time the animal lives than they produce their chloroplasts, ie in fact becomes a photosynthetic animal. This is highly beneficial to Elysia and you can get energy from photosynthesis by chloroplasts, just when the algae is not available as food.
Although Elysia can not "produce" their own functional chloroplasts these are kept for long periods of time, this shows that the shellfish must have their own genes that stabilize and support the survival of the chloroplasts.
We must remember that only chloroplast encoded their own DNA, 10% of the proteins needed to carry out photosynthesis properly. The remaining proteins are encoded in nuclear DNA of the algae. Therefore we say that the chloroplasts are semiautonomous organelles, as they have their own DNA and ribosomes, but can not live independently outside the cell, while in the cell cytoplasm can multiply by binary fission.
" As a shellfish may possess genes that maintain chloroplasts, organelles that are of plant origin?
The answer is apparently, in the horizontal transfer gene. Ie genes of the algae would have passed the mollusk.
This type of gene transfer between species has received increasing attention because of the considerable evidence accumulating in its favor and the importance of this gene transfer in evolution (where the virus may have played a major role, transferring genes between different species, both prokaryotes and eukaryotes).
With this in mind, the researchers searched the genome for genes that could stabilize Elysia chloroplasts. They found a gene that meets the psbO an important role in photosystem II. Moreover by comparing the gene of molluscum psbO the plant found which were identical.
All these findings suggesting that the gene was incorporated psbO horizontal gene transfer, since the animal has the gene from the zygote stage and their gametes.
Researchers have begun to show that the chloroplasts are active both by transcription and translation of their genes, even within animal cells, which demonstrates its functionality.
Another phenomenon known but no less fascinating is happening between algae and animals is the endosymbiotic process.
remember that Margulis speaks of a symbiotic planet and more precisely an endosymbiotic.
The endosymbiosis has been instrumental in aparcion of photosynthesis in eukaryotic organisms. This probably occurred early endosymbiotic event between a protist (eukaryote) and a cyanobacterium (prokaryote), which then gradually evolved into a chloroplast (intracellular organelles) due to mass loss and transfer of genetic material from the cyanobacteria to eukaryotic nucleus.
Figure 3. Hypothetical endosymbiotic events that have occurred throughout evolution of eukaryotic algae. It is also the current schematic symbiosis are conducting Elysia chlorotica and Vaucheria litorea .
Probably if this relationship between the alga Vaucheria and continuous Elysia sometime occur even greater gene transfer between chloroplasts and eukaryotic cells of the mollusk.
There is much to investigate and learn in this endosymbiotic relationship between Elysia and Vaucheria. Perhaps we are seeing the emergence of a new evolutionary branch, the photosynthetic animals and molluscs apparently taking the lead.
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