A new study published in Biological Bulletin by Julie A. Schwartz, Nicholas E. Curtis, and Sidney K. Pierce found something otherwise thought impossible within the animal kingdom: genes important to photosynthesis were found on the chromosomes of an animal, the green sea slug (Elysia chlorotica).


These sea slug genes help it sustain photosynthetic processes that provide it with all the food it needs. By incorporating genes for chloroplast repair into its own DNA (so onto its chromosomes), it is better able to support chloroplasts within its own cells, effectively bridging the world between animals which only have mitochondria and plants, which also have chloroplasts.

“There is no way on earth that genes from an alga should work inside an animal cell,” Pierce says. “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.”

It has been known since the 1970s that E chlorotica “steals” chloroplasts from algae and embeds them into its digestive cells. The oddity was that the green sea slug was able to maintain these cellular organs (organelles) for 9 months, far longer than would be expected even if these chloroplasts had remained in the algae. And until now, scientists were unable to explain how the sea slugs pull it off.

It is highly unusual to find DNA dealing with chloroplasts within the nuclear genome (so the slug’s own chromosomes) of an animal, and this presents the very first time this has ever been found. The fact that this is even theoretically possible, brings up questions of whether it really is possible that some very small percent of the human population can survive on primarily water and sunlight. It would be worthwhile to do a genetic analysis on the next person who makes, and appears to somewhat validate, these claims.

The next question is whether it is possible for even larger parts of chloroplast DNA to find a home in animal cells, and how the chloroplast repair DNA ended up within the slug’s chromosomes. Did random mutation, or an unexpected horizontal gene transfer during heat shock, introduce this DNA? It is likely that additional research will unveil the answers to these questions, and an eventual laboratory model could potentially open the door to new types of gene therapy.