Yet amazingly, there is an animal-that-screams-animal in which an alga also dwells. That would be the spotted salamander Ambystoma maculatum. When it is an embryo, cells of the alga Oophila amblystomatis somehow end up inside it. Technically, the salamander’s now a photosynthetic animal. This salamander is the sole known example of a vertebrate playing host to a symbiotic microorganism of any kind, photosynthetic or no. And needless to say, something very interesting — no one is yet sure exactly what — is going on between the 2. Past experiments have clearly shown that the salamander benefits from its unconventional living arrangements. How the algae feel about the situation has been rather less clear. Intracellular algae showed clear signs of stress and oxygen and sulfur deprivation, producing lots more heat shock and autophagy-related proteins in response to finding themselves inexplicably inside a salamander. So why does the Oophila, the salamander alga, put up with its apparently dreary living conditions inside its host? It’s an intriguing question that lacks a clear answer, but there are clues. The alga is found nowhere else in nature besides salamander egg capsules. Algal cells remain visible inside young salamanders for a long time. Even when they are no longer obvious, algal DNA remains detectable in adult salamanders in the oviducts and the male reproductive tract. Freshly laid eggs contain encysted algal cells. And those algal cells in the capsule don’t seem nearly as put-upon as those inside embryos. Where might they come from? Is it possible that the alga is passed from generation to generation of salamander, a perpetual part of the animal? If so, the salamander has given the algae the ultimate gifts: a free ride, a home, and immortality, at least for the life of the host species. If that is the case, it was probably a bargain worth making.

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