Which animals can photosynthesize

The only animal that photosynthesizes

... or the story of how I got my nickname "kleptoplast".

Photosynthesis, the conversion of light energy into chemical energy (e.g. sugar), is actually reserved for plants and some bacteria. If we could photosynthesize as humans it would be pretty handy, because then we could get some of our energy needs just by standing in the sun. But there is no animal that can do that, is there?

The green marine snails of the genus appear to be an exceptionElysia who live on the east coast of North America.

The green color of the snail is not only used to camouflage it against predators! It comes from intact chloroplasts (cell organelles that are actually the site of photosynthesis in plants), which are embedded in the cells of the digestive tract of the snail. The chloroplasts, however, have the snails from green algae (Vaucheria litorea) "Stolen", which are eaten and sucked out by the animals. All cell components except for the chloroplasts are discarded during this process.

The stolen chloroplasts (kleptoplasts) remain functional and even continue to express plastid genes while supplying the snail with carbohydrates. If you put an animal of the kind Elysia chlorotica In the youth stage in a lighted vessel, it survives up to nine months without food. This roughly corresponds to the normal life expectancy of the snail.

It cannot be taken for granted. Chloroplasts themselves are symbionts inside the plant cell; originally they must have been very similar to the photosynthetic cyanobacteria. In the course of evolution, large parts of the chloroplast genome have been transferred to the cell nucleus, where they are, for example, under better control of the host. More than 90% of the plastid proteins required have to be produced in the host cell and imported into the chloroplast. In the chloroplasts of the green algaeVaucheria litorea it is no different.
Two years ago it was discovered that the snail produces vegetable proteins and imports them into the kleptoplasts. So there must have been a horizontal gene transfer between algae and snail!

Addendum: On Ed Yong's blog you can read that in a new publication by W├Ągele et al.These findings could not be confirmed in the snail genome, there are no algae genes - how the chloroplasts can survive for months without a replenishment of repaired photosystems remains a mystery for the time being.

Here you can find out more about the snail and its algae (English language website).

Rumpho et al. (2008):Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica. PNAS 105(46) pp. 17867-71

Martin Ballaschk holds a PhD in biology, but is interested in many other natural sciences. The blog serves as a digestive organ for his thoughts. Professionally, he works as a science communicator, here purely privately.