A photosynthetic… Slug?

Whenever we think of photosynthesis, we imagine plants taking up sunlight and producing chemical energy and making food. We think that photosynthesis is something that is unique to plants. That is not the case, as there are many bacteria called cyano-bacteria or blue green algae (Although they are not the kind of ‘algae’ of plant kingdom, I know, it’s a bit weird classification) and some protistian single cell organisms –

And apparently now a slug.

The rich green color of the photosynthesizing sea slug, Elysia chlorotica, helps to camouflage it on the ocean floor. Credit: Patrick Krug

The bright green sea slug is called Elysia chlorotica is photosynthetic in nature and looks a lot like a veined leaf. (It looks so because of ‘convergent evolution’). How does an animal have the ability to perform photosynthesis?

This slug apparently incorporates the genes of algae that it eats into its own genome and ‘steals’ the algae’s photosynthetic machinery. Professor Sidney Pierce, a biologist at the University of South Florida and the University of Maryland, said: ‘There is no way on earth that genes from an alga should work inside an animal cell, and yet here, they do.

The entire chloroplasts of algae Vaucheria litorea and embeds into the cells of its digestive system. This means that even if it loses its food source, it can auto generate its carbohydrates by photosynthesis for 9 months. This turns its own cells bright green and its entire appearance looks like a veined leaf.

This incorporation is a good example of horizontal gene transfer, which basically is the transfer of genetic material from individuals to other individuals unlike a progeny type of transfer to off springs (which is vertical transfer).


-Aditya Karmarkar


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