It’s a tribute to the fantasticness of plants – and photosynthesis in particular – that even animals want to be like them. Arguably, none more so than some sea slugs, which for many millennia have eaten seaweeds and integrated their chloroplasts into their bodies (a phenomenon known as kleptoplasty). The assumption that underlies such acquisitive behaviour is that the new owners use those sequestered verdant powerhouses as a fuel source for their own purposes. A lovely idea – and one that will have found its way into the textbooks, and featured in lectures based thereon. But! Gregor Christa et al. have concluded that, while such ‘stolen plastids’ display light-dependent CO2 fixation (i.e. photosynthesis), light is not essential for the studied sea slugs – Elysia timida and Plakobranchus ocellatus – to stave off starvation. Indeed, they conclude that the internalized plastids seem to be a slowly digested food source rather than a source of solar power. In other words, this is an example of plants feeding the planet (again!). However, another bonus of this work is that animals are still just animals and not proxy plants. Which is good, because, to paraphrase one Harold Woolhouse, if one wants to understand the biology of plants one will ultimately have to work on… plants.
[However, if you wish to study animals that penetrate each other in the head during sex, then that’s where sea slugs really come into their own. But if you want more on photosynthetic animals, check out this article by Sarah Rybak – Ed.]