Scientists have long believed that only plants, algae, some bacteria, and a few invertebrates were capable of taking advantage of photosynthesis, which converts sunlight directly into energy. But now, for the first time, a photosynthetic vertebrate has been found, according to Nature.
The incredible creature is none other than the fairly common spotted salamander (Ambystoma maculatum). Ironically, the spotted salamander is not a new species for researchers, and it has long been known that the animal's embryos share a symbiotic relationship with photosynthetic algae. That relationship, however, was always assumed to be an outside one, whereby the algae and the salamander work separately toward a fair exchange of resources.
It turns out that researchers just weren't looking closely enough. While studying a batch of salamander embryos, scientist Ryan Kerney of Dalhousie University saw something different than the prevailing dogma would suggest — a bright green color coming from inside their cells.
That color usually indicates the presence of chlorophyll, which is the light-absorbing green pigment that makes photosynthesis possible.
"On a lark, I decided to take a long-exposure fluorescent image of a pre-hatchling salamander embryo," said Kerney. After backing that experiment up using transmission electron microscopy, he confirmed his suspicion. There were algal symbionts located inside the salamander cells.
In fact, the symbiotic partners were often found bordering mitochondria, organelles responsible for generating a cell's energy. Thus, it's likely that the mitochondria were taking direct advantage of the oxygen and carbohydrate, byproducts of photosynthesis that were generated by the algae.
The reason this discovery is surprising is because all vertebrates have what's known as an adaptive immune system, which naturally destroys any foreign biological material found inside the cells. How the algae in the salamander's cells bypass this defense is a mystery.
Even more interesting, Kerney also discovered that algae is present in the oviducts of adult female spotted salamanders, where the embryos form in their sacs. This means that it's possible symbiotic algae are passed from mother to offspring during reproduction.
"I wonder if algae could be getting into the germ [sex] cells," commented David Wake, from the University of California, Berkeley, who watched Kerney's presentation. "That would really challenge the dogma [of vertebrate cells disposing of foreign biological material]. But why not?"
Although this is the first time such a close co-existence with a photosynthetic organism has been found in a vertebrate, the discovery leaves open the question about if other animals might harbor similar traits.
"I think that if people start looking, we may see many more examples," said developmental biologist Daniel Buchholz.