Scientists from the University of Halifax in Nova Scotia, Canada have discovered photosynthetic algae living inside embryonic cells of the spotted salamander, providing them with extra power like a mean green energy drink. If true, this is the first known example of a vertebrate acquiring a new symbiont.
The spotted salamander is a salamander species endemic to North America. It lays eggs that are encapsulated in a thick layer of jelly. While this jelly protects the egg cells from predators and dehydration, it also makes it more difficult for oxygen to reach the innermost embryos and for carbon dioxide to dissipate. The embryo could die if these gases are exchanged too slowly. Luckily the salamander embryos receive help from algae that can be found within the salamander eggs. Since algae produce oxygen and take up carbon by photosynthesis, they are a perfect match with the growing embryos that struggle with their oxygen supply.
Close up of a single egg cell containing a salamander embryo and numerous algae growing within the egg. Source.
The symbiotic relationship between the single-celled algae Oophila amblystomatis and the spotted salamander has long been known. Its first appearance in scientific literature can be traced back to a publication by Henry Orr in 1888. He wrote:
I have not discovered how the Algae enter the membrane, nor what physiological effect they have on the respiration of the embryo, but it seems probable that in this latter respect they may have an important influence.
~ Henry Orr, Quart. Jour. Micr. Sci., N.S. 29: 295-324.
This observation turned out to be spot-on when Gilbert showed in 1944 that salamander eggs without algae hatched less often and produced developmentally retarded larvae. The algae also benefit from this relationship, as they receive nitrogen rich wastes from the developing embryo. They have never been observed outside of amphibian eggs. They thus appear to be just as dependent on the salamander embryos as they are on them. The name of this algal species (Oophila amblystomatis) couldn’t be more appropriate: it literally means “loves salamander eggs”.
Now, 122 years after the first discovery of this symbiosis, Ryan Kerney of Halifax University has shown that the embryonic salamander cells themselves contain algal symbionts. The first clue he received was that the salamander cells fluoresced in the dark, without any sort of staining. This hinted at the presence of chlorophyll, which is auto-fluorescent.
The Spotted Salamander: the happy host of the Oophila algal symbiont! Source.
Closer inspection with electron microscopy revealed that the algal symbionts really were located inside the cells. They were surrounded by mitochondria, the power plants of the cell. This suggests that the algae are directly fueling the mitochondria with oxygen and carbohydrates. Even cooler, Kerney also found the algae in the oviducts of salamander females. Maybe the algae are directly transmitted to the eggs and jelly sacks, as a sort of algal lunch box giving to the embryos by a caring salamander mother. I’m very anxious to see the time lapse video of the algae entering the embryo mentioned in the Nature news article.
Lots of questions remain to be answered of course. How does the salamander immune system recognize the algal symbionts as ‘self’ instead of invader? How are the algae maintained in the adult salamander? And could this short distance relationship develop into a more intimate one – where algal genes end up in the salamander, or where the algae themselves become a new organelle?
For now, this research shows that when close relationships between species turn into dependencies, intimate symbioses are not far away. Such symbioses can eventually blur boundaries between species and drive evolution in new directions. Sometimes, it’s occuring right beneath our noses, in model system that are a hundred years old. On a lighter note, how cool would it be to go to the beach, photosynthesize all day and go back home rejuvenated and refreshed? I’ll pour me an algae cocktail right away!
This research has not been published yet. When the paper hits the databases, I will include the link here.
1. Henrey Orr (1888). Note on the development of amphibians, chiefly concerning the central nervous system; with additional observations on the hypophysis, mouth, and the appendages and skeleton of the head Quarterly Journal of Microscopical Science
2. Gilbert, P. (1944). The Alga-Egg Relationship in Ambystoma Maculatum, A Case of Symbiosis Ecology, 25 (3) DOI: 10.2307/1931284
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Excellent post! I have a similar one on it too. Came across yours when I was putting together my own post.
Love the quote you posted by Orr and the mention of the work of Dilbert. You rock!
Thanks for the compliment, I like to dig the archives to see where the research came from. My way of paying homage to the ‘standing on the shoulders of giants’ motto I guess! And I have to say, your coverage is great as well!
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