Everyone probably knows what photosynthesis is. Everyone also probably knows, that plants are capable of photosynthesis. Also algae. And let’s not forget bacteria, the “inventors” of photosynthesis. But have you ever thought about why there are no photosynthetic animals? Or wondered, if there were any?
The truth is, that for most animals, photosynthesis is very inconvenient as a means of obtaining energy for various reasons. For example, we spend much of the day in the shade, as most animal
species do, and we have a very small surface area for gaining enough energy from sunlight.
But as we all know, for every rule there are some exceptions.
How do they do it?
There is not one particular way in which animals photosynthesize, or how they learn it. Every species has it’s own strategy to gain energy from the sun, some more efficient than the others. What
is common for some of the, otherwise completely unrelated species, is the act of stealing genes from another organism giving it the ability to photosynthesize.
You may also ask - why have I never noticed this, and you try to think if you have ever seen a green animal lying in the sun that might have been photosynthesizing.
So, which animals can photosynthesize and where do they live? I have chosen four species that I consider to be the most interesting, and now you have the opportunity to learn something about how they gather sunlight and turn it into the energy.
The pea aphid, or Acyrthosiphon Pisum in Latin, is a little bug that is interesting in the fact that it can photosynthesize, but also in how it reproduces - in the spring and summer the female gives birth to living offspring from unfertilized eggs, which are basically their clones, but in the autumn they reproduce sexually laying eggs that remain unhatched until the next spring.
But how is it possible that in addition to giving birth to it’s own clones, and not needing males for most of the year, it can also photosynthesize?
The answer is, in fact, very simple. This little animal, some time ago, stole a fungal gene giving it the ability to produce the pigment carotenoids, which enable the aphid to feed on sunlight. This is visible especially in orange-coloured aphids, which have the highest ATP (adenosine triphosphate - a source of energy) levels in direct sunlight.
Another insect, the oriental hornet, or Vespa Orientalis, if you like, has developed a completely different photosynthetic apparatus. It is the structure of its skin, called the cuticle, which gives it the ability to harvest the sunlight. This very sophisticated mechanism traps the sunlight so it can not bounce off the hornet’s body, and a pigment, called xanthopterin that the hornet has in the yellow coloured part of it’s body, converts the sunlight directly into electrical energy.
Because of this, the most of the metabolic activity in the hornet’s body is in its cuticle not in the “fat body” that is an equivalent of the liver in most insect species, and also the hornets are the most active around midday, not in the early morning as, for example, bees.
There has also been a hypothesis suggesting that maybe some other insects pose the pigment xanthopterin in their yellow stripes and thus the ability to photosynthesize!
Another, truly exceptional species is the spotted salamander - Abystoma Maculatum, that you might have seen in the woods around our town.
What is so exceptional about this animal is, that it is a photosynthesizing vertebrate, but also HOW it photosynthesizes!
The thing enabling this animal to photosynthesize is, in fact, its extraordinary immune system, that allows a green algae to form a symbiotic relationship with the salamander’s eggs, and allows the algae to live inside the embryo’s own cells, which would not be possible in another vertebrate species, for their immune system would kill the algae.
Though this system might be wonderful, it does not allow the salamander to photosynthesize for a very long time. When it hatches from the egg, the algae dies, and the relationship ends.
Emerald Sea Slug
The most perfect way for animals to feed on sunlight is the one developed by sea slugs. The sea slug, also called Elysia Chlorotica, has developed a way of stealing another animal’s genes, or,
more correctly, the whole chloroplasts, and using them to photosynthesize. This phenomenon is called “kleptoplasty”, and the slug’s victim is a simple green algae called Vaucheria Litorea.
What happens, is that the Elysia eats the algae, getting rid of everything but the chloroplasts, keeping them and their genetic information to carry on photosynthesizing.
Now, you may think, that this can’t be possible! Why?
Because the chloroplasts, despite carrying some genes, posses only fragments of the whole genetic information needed for their function. They, simply said, gave about 90% of their original genes to the nucleus. So the slug, despite having the chloroplasts, should be missing the majority of the information needed for the chloroplasts to function!
But the truth is, that a long time ago, the slugs, piece by piece, stole this needed information, incorporating it into their genome and passing it onto their offspring.
From now on, I hope that the next time you see a salamander you will know that as a little embryo it was feeding on the sunlight, and when you see a bee or a wasp you may contemplate what secrets their yellow strips hide.
I also hope that you will see nature a bit differently in the least, and that you will be able to see its genius and amazing resourcefulness in the ways of procreation, feeding, and basically, in keeping all it’s organisms alive. You also may think twice about how sophisticated and perfect it is.
by Daniela Kročianová
Year 1, Issue 2