This is a cool news story – scientists have found algae living inside the cells of a spotted salamander.This is an example of a plant-vertebrate symbiosis, the first documented. There are cases with invertebrates, like the sea slugs who can perform photosynthesis with proteins they acquired from algae.

It was previously known that certain species of salamander lived in symbiosis with algae, specifically the algae live outside the embryo and feed off nutrients in the embryo’s egg sac, while providing extra oxygen for the embryo. Embryos who develop in the absence of algae tend to develop deformities, so they appear to have evolved dependence on this extra oxygen from the algae. The new discovery is that the algae is also living inside the embryo – in the cells themselves.

The algae tend to suffuse inside the salamander during development, concentrating in the digestive tract, but also occurring elsewhere. It is still not clear if the algae comes in from the environment solely or if it is passed down from either parent. Researchers suspect that both occur.

There are other unanswered questions as well, including what functions the algae perform for the salamanders. Since they concentrate in the digestive system they may play a role in aiding nutrient extraction (like the bacteria in the intestines of other vertebrates, including humans). There is also interest in what other amphibian-algae symbiotic pairs might exist out there.

This symbiotic relationship sets up a situation in which both the algae and the salamander can co-evolve (which has certainly already been happening to some extent). This would be especially true for algae that spends its entire life cycle inside the cells of salamanders and are passed down from parent to offspring. The algae may become the equivalent of an organelle inside the salamander cells. This reminds me of what likely happened with mitochondria – they are the energy factories in eukaryotic cells, and likely evolved from primitive bacteria-like free living organisms. At one time mitochondria ancestors became symbiotic with the larger eukaryotic ancestors, but over millions of years became a completely dependent component of these cells.

I wonder what might become of the salamander-algae symbiosis and if it will evolve in a similar direction, to the point where the two species are no longer separable.