Scientists have stumbled across the first example of a photosynthetic organism living inside a vertebrate's cells. The discovery is a surprise because the adaptive immune systems of vertebrates generally destroy foreign biological material. In this case, however, a symbiotic alga seems to be surviving unchallenged — and might be giving its host a solar-powered metabolic boost. Algae cohabit with salamander embryos in their eggs — and inside their cells.T. LEVIN/PHOTOLIBRARY.COM The embryos of the spotted salamander (Ambystoma maculatum) have long been known to enjoy a mutualistic relationship with the single-celled alga Oophila amblystomatis. The salamanders' viridescent eggs are coloured by...