![]() So Artemia, to provide these partners-in-digestion with the ideal living conditions, is forced to live in water that’s saltier than it would naturally prefer, and is effectively barred from mildly salty places. And here’s the rub: the bacteria like salt. Without them, the shrimp wouldn’t be able to survive on their usual meals. These bacteria help to break down the carbohydrates in the algae, as well as detoxifying the many poisons in those mouthfuls. Their usual preference for high-salt water only exists when they eat algae and carry microbes. Likewise, when she fed them a diet of yeast instead of their usual meals of algae, they also did better with less salt. When Nougué raised Artemia larvae in sterile cultures, so they grew up without their usual coterie of microbes, these germ-free shrimp did better in low-salt water. Nougué discovered that Artemia’s gut microbes are behind this weird paradox. Bizarre! Surely, it should be the other way round? Below that threshold, they’re less likely to survive. At more than 40 grams of salt per litre, they’re fine. So you’d expect that Artemia does best in mildly salty water. The saltier the water, the harder they have to work and the more energy they burn. They cope with salt by efficiently pumping it out of their own bloodstreams. ![]() As their name suggests, they live in salty water, but they evolved from freshwater ancestors. These little creatures are more formally known as brine shrimp, or Artemia. Odrade Nougué and Thomas Lenormand from the University of Montpellier have found a great example of such constraints in an animal that will be familiar to anyone who grew up in the 70s and 80s: the sea monkey. Microbes can bar animals from valuable opportunities, restrict their options, and place burdens upon them-all without causing infections or disease. But symbiosis also comes with costs and constraints. These examples inform the common view that symbioses (partnerships) between animals and microbes lead to mutual benefit and expanding opportunities. ![]() By providing a source of energy that isn’t tied to sunlight, bacteria allowed worms, clams, and hundreds of other creatures to colonise the abyssal oceans, and lose their mouths and guts in the process. By breaking down the tough and typically indigestible carbohydrates in plant matter, bacteria allowed mammals to become extreme grazers and gave rise to the thundering herds of Africa’s plains. By providing nutrients that are missing from the sap of plants, bacteria have allowed bugs to subsist on a diet of nothing else, turning them into the bane of greenery and greenhouses worldwide. Time and again, microbes have opened doors for animals, allowing them to exploit niches that would have otherwise been denied to them by their basic animal-ness.
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