The sea slug that is fast-tracking evolution.

Let’s talk about Animals and Plants, from a very young age we are told that plants can photosynthesis their food from the suns energy, and animals tend to consume theirs. Now let me introduce the wonderful world of invertebrates that loves to be the exception to the rule book! Most people think of invertebrates as an insect, a small, brown, dull, and short-lived animal that you find running under the nearest leaf. Let’s talk about one of the many invertebrates that is possibly as far as possible from that idea, the green sea slug, Elysia chlorotic.


by Patrick J. Krug

This emerald green sea slug spends a lot of its time not eating; this would usually lead to death if it didn’t have the hidden advantage of being able to live of sunlight! Yes that is right, meet the animal that can photosynthesis quite happily under the sea. This sea slug may be on the right path here as now if it ever runs out of food it can still go on living for an extraordinary amount of time. Unfortunately this animal has not cracked the genetic code to be able to both digest nutrients and create sugars but eats algae and is able to incorporate its genes to allow for chloroplast to function in its cells. Now “There is no way on earth that genes from an alga should work inside an animal cell,” says Sidney Pierce from the University of South Florida. “And yet here, they do. They allow the animal to rely on sunshine for its nutrition. So if something happens to their food source, they have a way of not starving to death until they find more algae to eat.”

Chloroplasts are organelles in a plants cell that contain chlorophyll, a green photosynthetic pigment. Scientists have known since the 1970’s that this animal is able to ‘steal’ chloroplasts from that alga Vaucheria litorea, they can the embed the chloroplasts into their own cells, in the digestive tract, where these cells are able to carry on photosynthesizing for up to 9 months after absorption, this is longer then they would preform in algae! It is with these cells the slugs are able to sustain them selves in times of hardship.

Even though it has been known for a long time that these slugs can take & use chloroplasts, no one knew how they managed to maintain them. Thankfully now technology has been able to answer this question. DNA amplification, sequencing and advanced imaging techniques have all helped to reveal the sea slug’s chromosomes and be able to see the genes from the algae that code for both chloroplast proteins and synthesis present.

Now that we can see what is going on, scientists have found that several of the genes from the algae needed to repair damaged chloroplast and maintaining function is present. By incorporating these genes into the slugs own chromosomes and being able to transmit these to the next generation means that even though future slug populations will still need to harvest new chloroplasts from algae, the genes the slugs need to maintain them is already there.

With this revelation, these small sea slugs are one of the only known examples of a functional gene transfer between multicellular species. “When a successful transfer of genes between species occurs, evolution can basically happen from one generation to the next,” Pierce adds, rather than over thousands of years.

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A Behavioral entomologist. I love the little things that are often overlooked.

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