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SOURCES:
https://www.google.com/books/edition/The_Lost_Art_of_Finding_Our_Way/daT6AAAAQBAJ
https://www.hakaimagazine.com/features/secret-history-bioluminescence/
https://nwdistrict.ifas.ufl.edu/nat/2019/08/16/bioluminescence-light-show-beneath-the-sea/
http://tolweb.org/dinoflagellates/2445
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723414/
https://www.nature.com/articles/s41598-018-35785-7
https://www.ucl.ac.uk/GeolSci/micropal/dinoflagellate.html
https://www.sciencedirect.com/science/article/pii/S143446101500005X?casa_token=HuWLdTL7o1EAAAAA:Cc-aAg8ZqOzDR6GgLNdI1xhdufcjaNcE_-OaWaOGF406vSNLlOklZQ9Qz0c0aLsA1j-QeGBw
https://makingscience.royalsociety.org/s/rs/people/fst00108588
http://tolweb.org/notes/?note_id=5621
This episode is brought to you by EnergySage, the nation’s most trusted online solar marketplace.

Head to Energysage.com to start exploring rooftop and community solar options in your area. There are many organisms in nature that are capable of lighting themselves up through their own bioluminescent means.

But not many have the distinction of having helped guide a future astronaut to safety. Jim Lovell is perhaps best known for his flights to and around the moon, including the 1970 Apollo 13 mission, which experienced a critical failure that prevented it from actually landing on the moon. But in 1954, he was a fighter pilot on a training mission off the coast of Japan when his navigation systems failed.

With darkness around him and no guide to the aircraft carrier he was meant to land on, Lovell turned off the lights in his cabin…only to notice a glimmer of green in the waters below, acting like a trail of glow-in-the dark breadcrumbs left behind by the carrier as it moved through the water. That light was the bioluminescence of planktonic life, and fortunately, you don’t have to be a stranded fighter pilot to see it in action. That surface oceanic light is most likely attributable to a certain kind of single-celled eukaryote called a dinoflagellate.

There are more than 2000 living species of dinoflagellates, and while a few are found in freshwater, most are some form of marine plankton. Dinoflagellates survive on a mix of diets. Some are purely phototrophic, consuming food produced by their own chloroplasts.

But most are mixotrophic, meaning that they rely on a mix of photosynthesis and consumption. In either capacity, dinoflagellates are hugely important for their local ecosystems. As marine primary producers, they are second only to diatoms.

And when dinoflagellates consume other organisms, they link together various facets of production and consumption in the ocean, sending energy up the food chain. But nature is built on balance, and excess dinoflagellates can also become disruptive to local ecosystems when they accumulate into large toxic blooms, also known as “red tides”. These can choke off resources to other animals, and sometimes even produce toxins that poison their neighbors.

Aside from their importance, dinoflagellates are kind of quirky. For one thing, they have a really weird nucleus. Like so weird that it has its own name: the dinokaryon.

If “dinokaryon” sounds majestic to you, well… that is apt. The dinokaryon can hold a truly absurd amount of DNA for a eukaryotic nucleus. A human nucleus, just for reference, holds about 3 picograms of DNA.

Meanwhile, some dinoflagellates species can hold somewhere from 100-200 picograms of DNA in their dinokaryon. And where most eukaryotes pack our DNA into little structures connected together like beads on a string, dinoflagellate DNA does not have that clear of an architecture. Even more weird: they have the genes to make that kind of orderly arrangement possible, they just rarely seem to use them.

Dinoflagellates also swim kind of funny. It’s part of why we can’t show them too often because they’re always whirling in and out of focus. One is held in a structure around the organism’s equator, spinning and moving the organism forward.

The other flagella, which you can see here coming out the end of the dinoflagellate, helps the organism steer around. While most dinoflagellates are capable of photosynthesis, they do not all go about their chloroplasts the same way. Yes, some dinoflagellates have their own chloroplasts and use them as you would expect to carry out photosynthesis.

But others, like the freshwater Nusuttodinium, are a little bit less honest. They steal their chloroplasts. These dinoflagellates will start out chloroplast-less and colorless.

But as they begin to consume their favorite meal, some local photosynthetic algae, the dinoflagellates don’t just consume their nutrients: they steal the algae’s chloroplasts. These, appropriately enough, are called klepto chloroplasts, and they’ll stay with the dinoflagellate until they divide and the daughter cells have to steal some new ones. But of course, the most striking dinoflagellate trait is their bioluminescence.

When the organisms were first described by Henry Baker in the 19th century, he called them “animalcules which cause the sparkling light in sea water”. That sparkling light is the product of a molecule called luciferin, which is usually set into glowing action by some kind of mechanical stimulation. It could be the breaking of waves, a passing aircraft carrier, or—most relevant to the dinoflagellates themselves—a potential predator.

Scientists have hypothesized that dinoflagellates flash their lights as a kind of “burglar alarm” in response to predators, attracting the attention of other organisms that will eat the dinoflagellates’ own enemies. So, no, they’re not scaring away their predators. They are attracting the predators of their predators.

This system of bioluminescence and the molecules underlying it has its parallels across a lot of other animals, including fireflies. And whether they are taking in light for photosynthesis or producing it through their own pathways, dinoflagellates have evolved their own mastery of illumination. Thank you for coming on this journey with us as we explore the unseen world that surrounds us.

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