We all learned that plants get their energy from the sun through photosynthesis, whereas animals have to eat plants or other animals to get their energy. Well, it appears a sea slug named Elysia chlorotica, living in the western Atlantic Ocean, hasn't been to biology class.
This colorful green slug looks like a fancy leaf, and unlike other sea slugs, it uses the sun for energy, just like a plant. How does it do this? Elysia is a thief, and its thievery is known as kleptoplasty. When it's young, it eats algae which are loaded with chloroplasts. These small cellular organs which perform photosynthesis are absorbed by the slug's gut cells. From then on, the slug is solar powered and can make its own energy.
Chloroplasts should not be able to work once they are removed from algal cells because those cells contain proteins that control their operation. But they do work inside the slug. Scientists have discovered that Elysia not only steals chloroplasts, it has the genes to control their functions.
How this all happened remains a mystery. Scientists have found algal photosynthesis genes in both adult slugs and their eggs. This means the genes are part of the slug's genome and are passed from one generation to the next. Scientists suspect the genes were transferred from algae to sea slugs over evolutionary time, and are just now sequencing the entire genome of the slug to identify those transfers.
Some day we may discover exactly how Elysia became a thief, but even if we don't, it's certainly a great example of how diverse and interesting animals can be.