Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

Animals That Use Light Energy

Most people consider plants to be simpler creatures than animals, but plants and other photosynthetic organisms have one big advantage that animals lack. They have the wonderful ability to absorb light and simple nutrients and then make food inside their bodies. Researchers have discovered that some animals can also use light to make food in their bodies, though they require the help of a photosynthetic organism in order to do this.

The animals that perform photosynthesis contain captured chloroplasts or living algae containing chloroplasts inside their body. At least one animal species has incorporated algal genes into its DNA as well as algal chloroplasts into its cells. The chloroplasts carry out photosynthesis inside the animal, producing a carbohydrate and oxygen. The animal uses some of the carbohydrate for food.

Scientists have discovered that one insect can use sunlight, though it doesn't use it to produce food. Instead, its exoskeleton uses the light energy to produce electrical energy in a solar cell.

Four animals that make use of solar energy are a sea slug known as the eastern emerald elysia, an animal called the mint-sauce worm, an insect called the oriental hornet, and the embryos of the spotted salamander.

Solar-Powered Sea Slugs: Elysia chlorotica

The Eastern Emerald Elysia

Despite their relatively advanced anatomy and physiology, animal bodies can’t use the sun’s energy directly (except in reactions such as the production of vitamin D in human skin) and can't produce food internally. Their cells have no chloroplasts, so they are dependent on plants or other photosynthetic organisms for their survival, either directly or indirectly. The beautiful eastern emerald elysia (Elysia chlorotica) is one animal that has found an interesting solution to this problem.

The eastern emerald elysia is a type of sea slug. It's found along the east coast of the United States and Canada in shallow water. The slug is about an inch long and is green in colour. Its body is often decorated with small white spots.

Elysia chlorotica has wide, wing-like structures called parapodia that extend from the sides of its body as it floats. The parapodia undulate and contain vein-like structures, making the slug look like a leaf that has fallen into the water. This appearance may help to camouflage the animal. The parapodia are folded over the body when the animal is crawling over a solid surface.

These photos show a magnified view of the eastern emerald elysia. The arrow is pointing to one of the chloroplast-filled branches of the digestive tract in the parapodia. Karen N. Pelletreau et al, via Wikimedia Commons, CC BY 4.0 License

Algae in the Eastern Emerald Elysia

The eastern emerald elysia feeds on a filamentous green alga called Vaucheria litoria that lives in the intertidal zone. When it takes a filament into its mouth, the slug pierces it with its radula (a band covered with tiny chitinous teeth) and sucks the contents out. Due to a process that is not completely understood, the chloroplasts in the filament are not digested and are retained. The process of acquiring chloroplasts from the alga is known as kleptoplasty.

The chloroplasts collect in the branches of the slug's digestive tract, where they absorb sunlight and carry out photosynthesis. The branches of the digestive tract extend throughout the animal's body, including the parapodia. The slug's expanded "wings" provide a greater surface area for the chloroplasts to absorb light.

Young slugs that haven't collected chloroplasts are brown in color and have red spots. The chloroplasts build up as the animal feeds. Eventually they become so numerous that the slug no longer needs to eat. The chloroplasts make glucose, which the slug's body absorbs. Researchers have discovered that the slugs can survive as long as nine months without eating.

Though algae have chloroplasts and are sometimes casually referred to as plants, they don't belong to the plant kingdom and technically aren't plants.

Gene Transfer for Photosynthesis

The chloroplasts in a cell contain DNA, which in turn contains genes. Scientists have discovered that a chloroplast doesn't contain all of the genes needed to direct the process of photosynthesis. The other genes for photosynthesis are present in the DNA located in the nucleus of the cell. Researchers have found that at least one of the required algal genes is also present in the DNA of the eastern emerald elysia's cells. At some point in time, the algal gene became incorporated into the slug's DNA.

The fact that the chloroplast—which is not an animal organelle—can survive and function in an animal's body is amazing. Even more amazing is the fact that the sea slug's genome (genetic material) is made of both its own DNA and algal DNA. The situation is an example of horizontal gene transfer, or the transfer of genes between unrelated organisms. Vertical gene transfer is the transfer of genes from a parent to its offspring.

Mint sauce is made from mint leaves, vinegar, and sugar. It's a popular accompaniment to lamb in Britain and in some places is added to mushy peas. The name of the sauce is used for a tiny beach worm found in Europe. A group of mint-sauce worms looks much like the culinary sauce in some lighting conditions.

The Mint-Sauce Worm

A green worm (Symsagittifera roscoffensis) can be found on certain beaches on the Atlantic coast of Europe. The animal is only a few millimetres long and is often known as the mint-sauce worm. Its colour comes from the photosynthetic algae living in its tissues. The adult worms rely entirely on substances made by photosynthesis for their nutrition. They are found in shallow water, where their algae can absorb sunlight.

The worms collect to form a circular group when their population is sufficiently dense. Furthermore, the circle rotates—almost always in a clockwise direction. At lower densities the worms move in a linear mat, as shown in the video below. Researchers are very interested in the reasons why the worms move as a group and in the factors that control this movement.

Mint-Sauce Worms Moving Over a Beach

The Oriental Hornet

The oriental hornet, or Vespa orientalis, is a red-brown insect with yellow markings. The insect has two wide, yellow stripes next to each other near the end of its abdomen. The hornet also has a narrow yellow stripe near the start of its abdomen and a yellow patch on its face.

Oriental hornets are found in southern Europe, southwest Asia, northeast Africa, and Madagascar. They have also been introduced to part of South America.

The hornets live in colonies and usually build their nest underground. The nests are occasionally constructed above ground in a sheltered area, however. Like bees, the hornet colony consists of one queen and many workers, which are all females. The queen is the only hornet in the colony that reproduces. The workers take care of the nest and colony. The male hornets, or drones, die after fertilizing the queens.

The hard outer covering of an insect is called an exoskeleton or cuticle. Scientists have discovered that the exoskeleton of the oriental hornet produces electricity from sunlight and acts as a solar cell.

Oriental hornet workers fanning their wings to keep their nest cool on a hot day Gideon Pisanty, via Wikimedia Commons, CC BY 3.0 License

The Oriental Hornet Exoskeleton and Electricity

By examining the hornet's exoskeleton under very high magnification and investigating its composition and properties, scientists have discovered the following facts.

The brown areas of the exoskeleton contain grooves that split incoming sunlight into diverging beams.

The yellow areas are covered by oval protrusions which each have a tiny depression that resembles a pinhole.

The grooves and holes are thought to reduce the amount of sunlight that bounces off the exoskeleton.

Lab results have shown that the surface of the hornet absorbs most of the light that strikes it.

The yellow areas contain a pigment called xanthopterin, which can turn light energy into electrical energy.

Scientists think that the brown areas pass light to the yellow areas, which then produce electricity.

In the lab, shining light on the oriental hornet's exoskeleton generates a small voltage, showing that it can act as a solar cell.

The Scene Inside an Oriental Hornet Nest

Lab discoveries don't always apply to real life, but they often do. There is much to discover about solar energy use in oriental hornets. It's an interesting phenomenon.

Why May the Hornet Need Electrical Energy?

It's not yet known why the oriental hornet needs electrical energy, although researchers have made some suggestions. The electricity might give the insect's muscles extra energy or it might increase the activity of certain enzymes.

Unlike many insects, the oriental hornet is most active in the middle of the day and early afternoon when the sunlight is most intense. Its exoskeleton is thought to provide a boost in energy as sunlight is absorbed and converted into electrical energy.

The Spotted Salamander

The spotted salamander (Ambystoma maculatum) lives in the eastern United States and Canada, where it's a widespread amphibian. The adults are black, dark brown, or dark grey in colour and have yellow spots. Researchers have discovered that the embryos of the spotted salamander contain chloroplasts. The discovery is exciting because the salamander is the only vertebrate known to incorporate chloroplasts into its body.

Spotted salamanders live in deciduous forests. They are rarely seen because they spend most of their time under logs or rocks or in burrows. They emerge at night to feed under the cover of darkness. The salamanders are carnivores and eat invertebrates such as insects, worms, and slugs.

Spotted salamanders also emerge from their hiding place in order to mate. The female generally finds a vernal (temporary) pool in which to lay her eggs. The advantage of a pool of water compared to many ponds is that the pool doesn't contain fish that would eat the eggs.

Adult Spotted Salamanders

How Do the Embryos Obtain Chloroplasts?

Once the salamander's eggs are laid in a pool, a single-celled green alga called Oophila amblystomatis enters them within a few hours. The relationship between the developing embryo and the alga is mutually beneficial. The alga uses the wastes made by the embryos and the embryos use oxygen produced by the alga during photosynthesis. Researchers have found that in eggs with algae, embryos grow faster and have a better survival rate.

It used to be thought that the algae entered the salamander eggs but not the embryos inside the eggs. Now scientists know that some of the algae do enter the embryo's body, and some even enter the embryo's cells. The algae survive and continue to photosynthesize, producing food for the embryo as well as oxygen. Embryos without the algae can survive, but they grow more slowly and their survival rate is lower.

Salamander Eggs and Embryos

Animals and Photosynthesis

Now that one vertebrate has been found to carry out photosynthesis, scientists are on the lookout for more. They feel that it's more likely in vertebrates that reproduce by releasing eggs into water, where the eggs can be penetrated by algae. The young of mammals and birds are well protected and aren't likely to absorb algae.

The idea that animals can use solar energy vía isolated chloroplasts or algae or entirely on their own is a fascinating one. It will be interesting to see if more animals with these abilities are discovered.

References

Sea slug takes genes from algae from the Phys.org news service

Social sunbathing in the mint-sauce worm from the University of Bristol in the UK

Oriental hornets powered by solar energy from the BBC (British Broadcasting Corporation)

Algae inside the cells of salamander embryos from the Phys.org news service

Questions & Answers

Question: We use plant material like alfalfa (lucerne) to make pellets for animal feeds. Is it at all possible to "manufacture" pellets from sunlight with artificial photosynthesis and thus bypass the plants' processes?

Answer: At the moment, this isn’t possible. Researchers are exploring artificial photosynthesis, however, so it may one day be feasible. During natural photosynthesis, plants convert the energy of sunlight into chemical energy, which is then stored in the molecules of carbohydrates. At the moment, the focus of the artificial photosynthesis research seems to be the creation of a different type of energy from sunlight instead of the chemical energy stored in molecules. New goals for the research may be established in the future, though.

© 2013 Linda Crampton

Linda Crampton (author) from British Columbia, Canada on February 02, 2016:

Thank you for the informative comment, Taranwanderer.

Taranwanderer on February 02, 2016:

Great answer to Jamie's question! Also, even the oil we use is the result of long dead plants and animals that gathered sunlight into their cells during their life, and when they died, their remains were pushed down into the earth where the pressure and heat liquified the matter into oil (and natural gas). Everything, it seems, is sun-related

Linda Crampton (author) from British Columbia, Canada on March 03, 2015:

Hi, Jamie. Humans and animals depend on the sun for energy because although they don't use it directly they need it for their source of food. For example, humans feed on plants that have produced food inside their bodies using the sun's energy. We also eat animals that have fed on the plants, or even on animals that have fed on other animals that have eaten plants. The plants are at the bottom of the food chain. Without a light source, the plants wouldn't be able to carry out photosynthesis and make food. The death of the plants would then lead to the death of animals that feed on them.

Jamie on March 03, 2015:

My question actually is...humans and animals do not have chloroplasts in their cells and cannot photosynthesize. ..why are they still dependent on the sun for energy? If anyone can answer this. I would appreciate it.

Linda Crampton (author) from British Columbia, Canada on February 02, 2013:

Thank you, shiningirisheyes. It will be interesting to see what the future holds! We may find more photosynthetic animals and make discoveries that help humans.

Shining Irish Eyes from Upstate, New York on February 02, 2013:

The scientific studies being reached on a regular basis open up doors to an entire new realm of possibilities. Excellent research article.

Linda Crampton (author) from British Columbia, Canada on January 29, 2013:

Hi, drbj. They certainly are amazing animals! Thank you very much for the visit and the comment.

drbj and sherry from south Florida on January 29, 2013:

These three may be among the weirdest animals on the planet, Alicia. Thanks for bringing them to my attention is such a fascinating manner. I may have to interview one or all of them thanks to your introduction. They will join my hubs with other weird animals like the dung beetle, proboscis monkey, axolotl, anglerfish, platypus, etc., etc.

This hub is amazing. Trust me.

Linda Crampton (author) from British Columbia, Canada on January 28, 2013:

Thank you very much for the kind comment and the vote, Dianna!

Dianna Mendez on January 28, 2013:

I dont' know how you do it, but you continue to amaze me with these fascinating posts. The green insects look pretty. Thanks for the education. Voted way up!

Linda Crampton (author) from British Columbia, Canada on January 28, 2013:

Thank you for the visit, jainismus.

Mahaveer Sanglikar from Pune, India on January 28, 2013:

Interesting information, I did not know about this.

Linda Crampton (author) from British Columbia, Canada on January 27, 2013:

Thank you very much, girishpuri. I appreciate your visit and comment!

Girish puri from NCR , INDIA on January 27, 2013:

That is very useful and amazing information, animals use such an advanced technology, wonderful and an addition to my knowledge, thanks Alicia.

Linda Crampton (author) from British Columbia, Canada on January 27, 2013:

Hi, Tranquilheart. Yes, we do have so much more to learn about animals! Their features are so interesting. Thank you for the visit and the comment.

Tranquilheart from Canada on January 27, 2013:

We have much more to learn about animals of all types. Makes us realize that humans aren't superior, just different. Thanks & keep sharing.

Linda Crampton (author) from British Columbia, Canada on January 27, 2013:

It is a fascinating idea that an animal can carry out photosynthesis or that its body can act as a solar cell! Thanks for the visit and the comment, Deb.

Deb Hirt from Stillwater, OK on January 27, 2013:

This is amazing information. I had no clue that these animals were so advanced, which if you stop and think about it, they really are. I saw a spotted salamander once when I was a kid. Cute little thing!

Linda Crampton (author) from British Columbia, Canada on January 26, 2013:

Thanks for the comment, Martie. I appreciate it!

Martie Coetser from South Africa on January 26, 2013:

Extremely interesting information about animals using solar energy. I learn so much from you, Alicia! Thank you :)

Linda Crampton (author) from British Columbia, Canada on January 25, 2013:

Thank you very much, Rochelle! I appreciate your visit and comment. Yes, understanding photosynthesis and electricity production in animals could have important consequences in the future. It will be interesting to see what develops.

Rochelle Frank from California Gold Country on January 25, 2013:

Fascinating stuff! When scientists really understand all of this, I would suppose it could have major benefits for food and energy production.

Thanks for giving us a possible glimpse of the future. Good, content rich hub.