Cape Ann Vernal Pond Team

Biologist Nathan Mineo

Did You Know...?

Spotted Salamander Embryo and Algae Symbiosis

Written by Nathan Mineo 
Reprinted from the 2014 Cape Ann Vernal Pond Team Newsletter
Photograph by Cheryl Briscoe
Did you know that spotted salamander embryos have a symbiotic relationship with algae? This isn’t really breaking news; biologists have known of this relationship for quite some time. Victor Hutchison and Carl Hammen (1958) discovered that spotted salamander embryos obtain oxygen from the algae, Oophila amblystomatis, which grows within the gelatinous matrix of salamander egg masses. Most aquatic organisms’ egg-bound embryos obtain oxygen from the surrounding water by diffusion. Salamander embryos are no different, but they get an added boost of oxygen from the photosynthesizing O. amblystomatis. Remember, vernal pools are very low in oxygen, so this added oxygen from the algae makes life a little easier for the salamander embryos. Hutchison and Hammen also found that something more than oxygen from the algae, a “growth-stimulating substance” perhaps, was responsible for the increased growth, increased hatchling size, and increased survival of salamander larvae. But what...?

Fast forward to 2013 and we know A LOT more! Multiple studies have shown a number of benefits enjoyed by salamander embryos hosting this algae. For starters, it inhibits bacterial growth, which is a major killer of salamander embryos. Also, not only does the algae grow within the matrix of the egg mass, it surrounds and even penetrates the individual eggs. That alone is pretty amazing, but what about the “growth-stimulating substance”? To understand that, we need a quick biology refresher. 

Carbon and nitrogen are excreted by animals (like salamander embryos) in the form of inorganic molecules. This carbon and nitrogen waste is used by algae and converted back into organic molecules (essentially food) that can be used again by animals. This is called fixation. We know the process of carbon fixation by the name photosynthesis, which also produces oxygen as a byproduct of carbon fixation.

Salamander embryos are animals and, in order to grow, need a supply of nutrients and must excrete waste. O. amblystomatis, removes and uses the carbon and nitrogenous wastes excreted by the embryos. The inorganic carbon, in the form of carbon dioxide (what we animals exhale), is photosynthesized by this algae and turned into food and oxygen which is directly used by the salamander embryos. It’s as though O. amblystomatis is feeding the live embryos while they are still in their eggs! This is how embryos in egg masses with the algae develop faster than embryos without it. It is very rare to find a salamander egg mass that does not have this particular algae. In fact, most embryos in masses lacking O. amblystomatis end up dying. The embryos are almost dependent on the algae for survival.

This type of symbiotic relationship is well known among invertebrates, but it was unheard of among vertebrates until recently. Erin Graham and colleagues were the first to publish a paper, in 2013, showing evidence of a symbiotic relationship where fixed carbon is directly transferred from a photosynthesizing organism to a vertebrate host. So next time you visit a vernal pool, take a look at the salamander egg masses. Chances are the eggs are tinted green with O. amblystomatis, and the embryos inside are receiving nutrients directly from the algae.

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