Although it looks like a regular salamander, the yellow spotted salamander is completely unique because its embryos use the sun for energy. They have algae inside of their cells that give them oxygen and carbohydrates. This feature that though, of course, necessary in green plants, is not so common in animals. A sea slug, aphid, and hornets are other creatures that share this ability. However, the yellow spotted salamander (Ambystoma maculatum) is the only known photosynthetic vertebrate! In fact, before this finding, it was thought to be impossible.
What is yellow spotted and secretly green?
Yellow spotted salamanders actually look pretty normal; they aren’t green or anything. As the name suggests, the salamander is black with yellow spots. It is very common in North America. However, while the embryo is developing it undergoes photosynthesis. The reason why has to do with the salamander’s life history. The adults go to pools of water to mate and breed. Yellow salamanders only breed in ponds without fish because, otherwise, their larvae would be gobbled up. However, fishless ponds don’t contain very much oxygen. This problem is solved by adding algae into the mix.
It has been known for a long time that the eggs have a symbiotic relationship with algae; the eggs are bright green. Only recently, a researcher from Dalhousie University in Nova Scotia discovered that at a certain period in their development, embryos contain algae within their cells. Part of the green colour of the eggs comes from the embryos themselves.
A two-way relationship
The algae only move into the embryo after parts of the salamander’s nervous system has developed. Looking at time-lapse videos, you can see a flash of green at this time, which is a small algae bloom. The developing embryo releases nitrogen-rich waste at about this time, giving the algae food. Some algae could make it in the embryo at this time.
Once in the salamander, the algae stick near its mitochondria. Mitochondria create energy for animal cells from oxygen and a metabolic form of glucose. The algae appear to be giving oxygen and carbohydrates (the products of photosynthesis) directly to the salamander cells that contain them. The salamander could be using these byproducts to help its own energy production. In return, the embryo gives the algae nitrogen-rich waste and CO2. The algae have also been found in the oviducts of female spotted salamanders. The mother may have the algae already and be passing it down to its offspring by putting it into the egg sac.
The yellow spotted salamander is the first vertebrate to have a photosynthetic symbiont. Before, it was thought to be impossible because vertebrates have an adaptive immune system that should destroy any foreign biologically material. Therefore, it was believed that vertebrates weren’t able to have a symbiont living in them. The spotted salamander may have gotten around this obstacle by turning their immune system off or by the algae not being recognised as foreign. However, the real answer isn’t known yet.
As mentioned, photosynthetic animals are extremely rare and all of the other known cases are invertebrates. The others use slightly different methods to harness solar energy, most commonly by containing some form of microalgae or cyanobacteria inside of them. For example, the emerald green sea slug, Elysia chlorotica, even has genes to sustain the chloroplasts that it contains. It can live for up to nine months without eating anything. The pea aphid (Acyrthosiphon pisum) has a fungal gene that produces carotenoids. A bit differently, oriental hornets (Vespa orientalis) conduct electricity from their exoskeletons, silk, and comb walls. The hornet’s yellow bands contain xanthopterin that absorbs light and turns it into electricity. Unfortunately, this same material makes an inefficient solar panel.
All in all, the yellow spotted salamander is unique in being able to photosynthesize. It has shattered previous perceptions and opened the idea that other vertebrates may also have a symbiotic relationship with algae. So there you have it— salamander embryos that take energy from the sun.