An overview of the symbiosis between Ambystoma maculatum and Oophila amblystomatis

In recent studies, it has been shown that a symbiosis exists between the green alga Oophila amblystomatis and the developing embryo of Ambystoma maculatum, also known as the spotted salamander. In this relationship, the algae resides in the embryo's egg and makes use of it's nitrogen-rich waste. In return, the algae supplies the embryo with photosynthetic oxygen and carbohydrates. The increased oxygen levels benefit the embryos by speeding up development, stimulating simultaneous hatching, and decreasing embryo mortality. Previous studies have indicated that the algae inhabit the eggs shortly after deposition and their numbers drastically increase in the earlier stages of development. This is followed by the algae becoming immobile and congregating in the inner egg envelope right next to the embryo. The purpose of the recent experiment conducted by Erin Graham, Zaid McKie-Krisberg, and Robert Sanders was to track levels of carbon transfer between the algae and salamander egg throughout development. A. maculatum eggs were collected and incubated in the lab in 8C fresh water on a light/dark cycle of 12 hours. Embryo stage was determined using two previously used methods and the outcomes were compared. Fixed carbon translocation was measured in the eggs at six points in the later stages of development. The results of this study support the previous research and also determined that the algae began giving carbon to the embryo during the middle tailbud period of development (stages 26-30), but this was only observed in 20% of samples. Peak carbon transfer was observed in stages 31-35 with 87% of samples. This was followed by a decline and by five days prior to hatching 0% of samples showed carbon transfer. The researchers conclude this trend is most likely due to the rapid growth of the algae in early stages, which eventually settles and stabilizes in the inner egg envelope where translocation takes place. Additionally, the decline of translocation in the latest stages of development is due to the thinning and eventual bursting of the egg envelope in preparation for hatching. 
This study is an important contribution to the understanding of how organisms interact symbiotically. This relationship gives the spotted salamander a competitive advantage to other salamanders that do not have supplemented nutrients. Not only can this help the embryo survive until hatching, but it can also produce a stronger individual that can better survive in harsh conditions after hatching. Larval salamanders can be especially sensitive to aquatic conditions and competition for resources as well as predation both inter and intra-specifically. The increased hatching size that may be a result of algae-supplemented nutrients could help these individuals better compete and survive to maturing so that they can reproduce. I think it would be interesting to do similar studies on other salamander or anuran embryos to determine if this type of relationship exists elsewhere. 

The image above is of a spotted salamander that has just laid her eggs in a body of water that may contain Oophila amblystomatis.

source: Graham, Erin R., Zaid M. McKie-Krisberg, and Robert W. Sanders. "Photosynthetic carbon from algal symbionts peaks during the latter stages of embryonic development in the salamander Ambystoma maculatum." BMC Research Notes 7 (2014): 764. Academic OneFile. Web. 27 Apr. 2015.