“The developing eggs of this species of Amblystoma [sic] seem to present a remarkable case of symbiosis... 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 1888
Direct associations between photosynthetic algae and vertebrate animals are rare. It is therefore striking to observe the green eggs of the spotted salamander in the Eastern United States. Even more remarkable than the algae colonizing the egg was the observation that the algae can also commonly be found in salamander embryo tissues and even within cells (see here and here). This is the first known vertebrate-alga endosymbiosis, reminiscent of the interactions that drive the formation of coral reefs, but with the added complication of vertebrate adaptive immunity. In the Burns lab we are exploring many aspects of the salamander-alga symbiosis, with a particular focus on the chemical dialog between host and symbiont during the intracellular association.
Freshly laid egg masses can be clear or cloudy. Algae are not visible initially. After some time, algae bloom inside the eggs in both clear and cloudy egg masses and interact with the salamander embryo forming ecto- and endo-symbioses. Image credit: E.Chapman/AMNH
Spotted salamander eggs containing both algae and embryos can be removed from the egg mass for individual study. Image credit: E.Chapman/AMNH