Well the CBC news piece tells the story, but a team of researchers (Kerney et al. 2011) at University of California (Berkeley) has recently discovered a symbiotic association between spotted salamander (Ambystoma maculatum) embryos and Oophila amblystomatis (literally translates to 'salamander egg lover') green algae. Green algae have long been known to colonize spotted salamander eggs, but here they have actually observed the algal cells within the embryonic tissue (endosymbiosis).
(Oophila sp.)
Oh, and before I go any further I’d just like to address a little sticky point (spurred on by one of the comments on the CBC news page)… algae are not plants (kingdom Plantae), they are protists (kingdom Protista). Yes, both groups are eukaryotic, and some protists can photosynthesize, but they are not even remotely the same.
Similar associations have been documented in many invertebrates, like sea anemones, jellyfish, and nudibranchs. But this is something special because endosymbiosis is incredibly rare in vertebrates; so much so that this appears to be the first documented case.
Symbiosis is shockingly common in nature. Lichen, and fungal mycorrhizae associated with vascular plant roots are two well-known examples that are easy to observe. Even the mitochondria on our cells, or chloroplasts in plants (and other membrane-bound organelles) are the legacy of endosymbiosis past. The difference between the origins of mitochondria and the newly discovered association with spotted salamanders is that the ancestral symbiotic event involved single-celled organisms, and likely some error in phagocytosis (the act of a cell consuming another by enveloping it, like an amoeba) or some form of parasitism. It is even possible to track the evolution of chloroplasts through multiple endosymbiotic events by counting the number of plastid membranes in some groups or organisms, like dinoflagellates.
This new symbiosis involves a multi-cellular vertebrate being ‘invaded’ by a single-celled organism. But the nature of this symbiotic relationship remains unknown. How do both parties benefit? Kerney et al. (2011) speculate that the embryos gain some advantage during development from elevated oxygen levels in their tissue provided by the algae. But what does the algae gain? True symbiosis is a form of mutualism. They could very well, as Kerney suggests, gain carbon dioxide and nitrogen from the embryo. It could also be that the algae gain some measure of protection from being inside a larger organism, but amphibian eggs are preyed upon by many other species. And what happens to the algae once the embryo develops to the point where light can no longer penetrate the tissue? Obviously there are still unanswered questions, which makes this discovery all the more enticing.
Symbiosis was a key development right near the dawn of our tree of life that spawned the incredible diversity we enjoy today. Symbiosis is everywhere, which suggests that the secret of life might not be competition (‘Nature red in tooth and claw’), but rather how well organisms are able to get along.
I like that.
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