Thursday, August 26, 2010

Science of Symbiosis in the Solar-Salamander.

                                                      spotted salamander (source)

Be forewarned!...Another long-held scientific-dogma could be in the pipeline for complete annihilation! gulp further, and faster...[sorry for sounding like the eager foreword of a naive novella]...but this story IS as seductive as it can get...

For long, scientists heve believed, with good reason though, that the vertebrate system owing to it's highly specialized and robust adaptive-immune system rejects anything that is not 'self'. It translates into the following - It is impossible for a symbiont to live and propagate 'inside' a healthy vertebrate body, without retaliation from the host's immune system! Period!

         (A) Individual eggs within a salamander egg-mass, with tiny green alga Oophila, which provides the greenish appearance.

..Not any more, says Ryan Kerney of Dalhousie University in Halifax, Nova Scotia, Canada (Ryan is here). And the basis for this new-found boom in Ryan's voice comes from his close observations of a clutch of spotted-salamander (Ambystoma maculatum) eggs, which are green in appearance. He watched and watched and noticed something really extraordinary in those otherwise mundane and oft-studied eggs.

He realized for the first time, that the salamander eggs have a intracellular-guest - the single-celled alga, Oophila amblystomatis! Actually, these alga are generally called "salamander algae", and are a species of single-celled alga. The Latin specific name actually translates into "loves salamander eggs". And, it is these alga which give the characterisitc emerald-green colour to the salamander embryos as well as the jelly capsule that encases them.

Interestingly, it had been earlier known that the algae enjoy a symbiotic relationship with the spotted salamander, which lays its eggs in bodies of water. However, the symbiosis was thought to occur between the salamander embryo and algae living 'outside' it — a relationship hinging on the embryo producing nitrogen-rich waste that is useful to algae, and the algae reciprocating with increasing the oxygen content of the water in the immediate vicinity of the respiring embryos...but this new observation totally destroys the paradigm of symbiosis without far so good....

 (B) Detail of a single image. Head and gills of the dark, developing embryo are visible and the tiny green dots are the endosymbiont algae (source for A and B). 
Ryan goes on to suggest, that the green alga could be directly providing the products of photosynthesis — oxygen and carbohydrate — to the salamander cells that encapsulate them, thus making them energy-sufficient! This is indirectly-evidenced by Transmission Electron Microscopy (TEM) images which show several mitochrondria (which are the 'powerhouses' of animal cells, converting oxygen and a metabolic product of glucose into ATP, a molecule that cells use to store chemical energy) bordering the algal symbiont in the salamander cells. So salamander mitochondria gathered around an algal cell might be there to take advantage of the oxygen and carbohydrate generated by photosynthesis in that particular cell.

An earlier study by Lynda Goff, a molecular marine biologist and a host-parasite-interaction specialist, at the UC, Santa Cruz, who worked on this pair of organisms about 30 years ago, had successfully demonstrated, among other things, that embryos lacking algae in their surrounding jelly are slow to hatch also saw a logarithmic increase in algal cells as the embryo developed, and in those that did contain algae, the community was not static.

The question however remains as to how are the algal-cells present in the embryos evade self-destruction? Ryan says the it could be that either the salamander cells have turned their internal immune system off, or the algae have somehow bypassed it.

Another interesting question could be to probe the mode of entry of the algae inside the embryos?
A naturally happening likely moment is when the embryos' nervous systems begin to form. A time-lapse video made by Roger Hangarter at Indiana University in Bloomington reveals a fluorescent green flash next to each embryo at that point in its development. The flare is a bloom of algae, which is probably drawn to a release of nitrogen-rich waste from the embryo. Ryan postulates that if waste is released, then there must also be a way in — and the large number of algae in the bloom increases the chances that some will make it in...fair logic!

One of Ryan's most curious discoveries is of the presence of algae in the oviducts of adult female spotted salamanders, where the embryo-encompassing jelly sacs form — a finding that points to the possibility that symbiotic algae could be passed from mother to the offspring's jelly sacs during reproduction. Therefore is this a maternal-gift? This in turn raises another possibility - that whether algae could be getting into the germ [sex] cells.  That would really challenge the dogma [of vertebrate cells disposing of foreign biological material].

Now, is this smacking of Epigenetics? Inheritance that is modulated not by DNA,  and in this specific case, not even by intracellular molecular factors, but at an organismal level? Big Question.

The salamander happens to be an interesting animal - most of its cells retain a degree of pluripotency. That is, the animal has the capability to regrow its lost limbs when it loses them (remember the common Gecko which lets off its tail when threatened and usually regrows it)...does this mean that such animals have different modes of 'self' and 'non-self'-recognition?

The answer probably is very easy.....we have absolutely No-Idea at this point! 

Food for Thought? Yes. Yes.


* Green Eggs and Jam: Adaptations That Help Spotted Salamanders Reproduce (here).

* Green eggs power solar salamanders (here).

* Salamander's egg surprise (here)

* A solar salamander (here)
* 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
* Gilbert, P. (1944). The Alga-Egg Relationship in Ambystoma Maculatum, A Case of Symbiosis Ecology, 25 (3)

1 comment:

  1. Very interesting to say the least !! thanks for picking up such amazing topics.
    One question. How come it was known for so long and all the other guys missed it??