In this post, we’ll look at the strange world of solar-powered animals. These creatures somehow learned to harness the power of the sun and live like a part plant, part animal.
Plants are autotrophs, which harness the sun’s power to provide most of the food they need to grow. Through photosynthesis, they can take sunlight and carbon dioxide and change it into sugar for food. Fortunately, the process releases oxygen, essential for (most) life on Earth.
In this world where “going green” is more important than ever, wouldn’t it be great if animals could do it too? As it turns out, a few of them can – living in symbiotic relationships with algae in their bodies. Inside the algae, organelles called chloroplasts contain green chlorophyll, lending a green color.
Let’s take a look at some rare solar-powered animals, which unsurprisingly tend to look green. (but not always)
Solar-powered animals That Change the Planet
It has long been known that many reef-building corals contain photosynthetic algae, called zooxanthellae. Thus, these tiny photosynthetic invertebrate animals create structures that can be seen from space. Reefs are the largest structures of biological origin on Earth.
Since corals remain in one place most of their lives, they function similar to a stationary plant. In this case, it’s called being sessile. However, they differ from plants in that they don’t make their own food. Inside the coral’s bodies, microscopic zooxanthellae live in mutually beneficial symbiosis.
Therefore, corals are solar-powered animals.
Safely protected, the tiny algae take advantage of the coral’s metabolic waste products, removing them. In return, the coral receives oxygen and the products of the algae’s photosynthesis.
Due to climate change, corals respond to warmer water and acidity by expelling dying algal cells. It’s a process called “bleaching.” Unfortunately, bleaching eventually kills the reef and is a major concern for the Earth’s oceanic food chain.
More about corals and their symbiotic relationship with algae from Bozeman Science:
Leaf Sheep: Solar-powered Bovines of the Sea?
One doesn’t generally think of a sea slug as adorable, but Costasiella kuroshimael, the “Leaf Sheep,” truly is. Although it’s called a sheep, it looks to us like some kind of cartoon cow, with tiny beady eyes. Plus, it has horn-like rhinophores and pink nose-like spots that add to the cartoon look.
Found at the Great Barrier Reef, Japan, Indonesia, and the Philippines, these solar-powered animals mostly go unnoticed. For one thing, they are incredibly tiny, at only a maximum of one centimeter long. Otherwise, they are covered in green leaf-like appendages that make them look like an artichoke.
As Leaf Sheep feed on algae, they can steal the chloroplasts to use in these leaf-like parts. The process is called kleptoplasty, from the Greek for thief and chloroplasts. Thief or not, these creatures are ridiculously cute up close!
See more about the Leaf Sheep below from Ben G Thomas:
Eastern Emerald Elysia
Along the coast of the eastern United States, solar-powered animals are slowly creeping along. However, we bet you’ve never seen one, or wouldn’t know if you had. Why? The Eastern Emerald Elysia sea slug, Elysia chlorotica, exactly resembles a leaf, with no resemblance to a bovine.
Interestingly, the leaf appearance is not just a disguise since the creatures function pretty much like a leaf. Most of the time, they don’t consume food but absorb sunlight to meet all their energy needs.
Like the Leaf Sheep, this creature uses kleptoplasty. Thus, its digestive system can sort out the chloroplasts from algae and moves them to its skin.
Even more impressive, the slug borrows genes from the algae, which allows it to produce proteins needed to maintain the chloroplasts. Then, the Elysia can go for months relying on the power of the sun.
See the Eastern Emerald Elysia in action from Strange Animals:
Solar-powered Pea Aphids
In the strange world of aphids, Pea Aphids are notable for producing their own carotenoids that work similarly to photosynthesis. All animals aside from this aphid have to obtain carotenoids like beta-Carotene from plants. Somehow, the tiny bugs acquired to skill to make their own.
Notably, the aphids are not truly photosynthetic. However, the carotenoids capture sunlight and produce electrons that aid the production of energy. Thus, pea aphids can use this skill to create adenosine triphosphate (ATP). The greener the aphid, the more ATP they tend to produce.
You might recall from a biology class, ATP is the same molecule that plants create through photosynthesis. Humans also make ATP inside the mitochondria of the cells.
See more about the Pea Aphids and more from SciShow:
Solar Spotted Salamander
This one is perhaps the strangest of all, but the beautiful spotted salamander, Ambystoma maculatum, is the only known solar-powered vertebrate. Although they don’t appear green, they contain chlorophyll-containing single-celled alga all over their bodies.
When spotted salamanders breed, the algae can be seen in the fertilized eggs. From there, the algae remains a part of the salamander’s body.
Living in symbiosis, single-celled alga, Oophila amblystomatis, may provide oxygen and carbohydrate to the salamander cells.
In most similar situations, an animal’s immune system would attack the foreign cells, but not in this case. Somehow, the salamander’s cells have either turn off their internal immune system. Otherwise, the alga somehow bypasses the immune system.
Before this discovery, it was known that corals similarly co-exist with photosynthetic organisms. However, this is the first time a vertebrate is known to do the same.
See more about the Spotted Salamander from Ben G Thomas:
Could Humans Become Photosynthetic?
Unfortunately, it’s unlikely that humans could harness photosynthesis to provide enough energy. Even if we could grow chloroplasts in our skin, we tend to need much more power than a stationary plant.
This is probably why the Audrey II monster plant in the movie “Little Shop of Horrors” required more than sunlight – much more!
Moreover, consider the energy needs of plants. While a typical tree requires 200 calories a day, a human requires more like 2000. Also, there would be little time for anything other than sitting mostly naked in the sun. Of course, this might be great while on vacation at the beach, but not great otherwise.
Humans have large brains requiring high energy, and the ability to walk around makes that even higher. Thus, the sugars created through photosynthesis would not be enough. Plus, we’d still have to consume food to get the proteins we need at the very least.
So, sadly, humans will probably never be solar-powered animals. As Kermit says, it’s not easy being green.
See more about humans and photosynthesis from Reactions: