KNOWABLE MAGAZINE - n warm, shallow waters, a spiny, slug-like creature grazes on bacterial sludge on the seafloor, while sponges nearby filter clouds of suspended particles. A shell-encased Odaraia swims past, picking smaller life forms out of the water, while a giant Anomalocaris, with its formidable grasping appendages, prowls for soft-bodied critters. It’s a scene from some 500 million years ago, of oceans teeming with a new kind of life — the up-and-coming kingdom of animals.
Animals, made of many cells and feasting on other life instead of manufacturing their own nourishment from scratch, were an evolutionary hit. But this way of living brought complications. Early in the kingdom’s lineage, animals lost the ability to make nine of the 20 amino acids needed to build proteins.
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All 36 Hawaiian species of Pariaconus psyllids host the Carsonella bacterium, but many also get essential amino acids that Carsonella doesn’t produce from Makana and Malihini. The precise makeup of these bacterial communities evolved as their insect hosts adopted different diets and thus had different needs, explains entomologist and evolutionary biologist Allison Hansen of the University of California, Riverside.