Wednesday, 4 August 2010
Solar-powered Amphibian Gets Algae Out and About
From the latest on-line edition of the prestigious scientific journal Nature, the story of an alga that lives inside salamander cells.
And not only living there, but providing the animal with oxygen and food. This is the first time pigment algae have been found inside the cells of a vertebrate (animals with backbones, like us).
Anna Petherick reports that the close relationship between alga and salamander was discovered by chance after studying this beast for decades. The researchers from Dalhousie University in Halifax, Canada, noticed that the bright green colour of the Spotted Salamander embryo came from inside the embryo as well as in the jelly like capsule around it.
They call this lovely bright green colouration 'viridescence', and it's caused by an alga called Oophila amblystomatis. This alga is spherical and consists of a single cell. We phycologists call it a green alga, because it's green and it is in the Chlorophyceae group (or the latest incarnation of this group as we resolve the classification of the algae using DNA).
It was already known that this green alga had a 'relationship' with the Spotted Salamander. Until know though, it was thought to be a little more aloof, with the algae living outside the animal. The embryo produces waste that contains nitrogen, something that is useful to the alga. The alga, for its part, increases the oxygen levels in nearby water, which is useful for the solamander.
The hot discovery is that Oophila are 'commonly' found inside the cells of the salamander. It looks like the algae provide not only oxygen but the other product of photosynthesis - sugars or carbohydrate - for the lucky vertebrate.
This kind of thing goes on in corals and I think sponges but it hasn't been detected in vertebrates. Generally vertebrates are good at killing things they don't like using their immune system, and this kind of relationship (a symbiosis) was considered impossible. So either the Salamander has turned off the immune system or my algal friends have found a way to get round it.
The salamander cells harbouring the helpful algae have 'mitochondria' (the compartments inside cells where oxygen and food are converted into energy) siding up to the algal cell, suggesting that they have learnt how to make good use of the Oophila produce.
The researchers don't yet know how the algae get into the cells, but they are working on it. An American algal specialist Lynda Goff has been working on these two organisms - the alga and the amphibian - for about 30 years and she was well aware of the advantage of Oophila to the salamander embryos. Her work suggests the algae divide rapidly once inside the embryo, and increasingly so as the embryo develops.
It seems the point and time of entry might be where and when the nervous system begins to form in the little Spotted Salamander embryo. Waste goes out at this time so an alga could go in.
The reason it has taken so long to discover this important relationship seems to be because algal numbers are probably very low at the time most embryos are studied. Later in development the alga blooms and becomes more obvious, even though it may have been there almost from the start.
The leading researcher, Ryan Kerney, also disovered some of our algal friends in the part of the female Spotted Salamander where the embryo sacs are formed. So this may be were the relationship begins for the next generation. Oophila may even be entering the sex cells of the salamander, which would be a dramatic change to accepted wisdom.
And it's possible similar relationships exist in other salamanders and we just need to look a little closer. So lots of interesting research to be done here.
Clearly, though, this is a great way for algae to get out and about.
Image: Not the green alga in question, but a green alga a bit like the green alga in question (at least to a non-phycologist).