Every evening, nocturnal Hawaiian bobtail squids (Euprymna scolopes) emerge from their burrows in shallow waters of the Pacific to hunt for shrimp. These soft-bodied, golf-ball-size cephalopods don’t have much to protect them from predators such seals, eels, and fish. So they rely on another organism to help out: the bacterium Vibrio fischeri. This microbe lives in an organ embedded in the squid’s ink sac and emits light throughout the night to match the illumination of the moon.
“It is basically acting like a little invisibility cloak for the squid,” said Jamie Foster, a microbiologist at the Space Life Sciences Lab at the University of Florida. In return for help with camouflage that protects against predators, the squid offers up sugars to feed the bacteria and lure them into the organ.
This mutually beneficial relationship has evolved over millions of years and is one of numerous examples of how multicellular animals and microbes work together to increase their chances of survival. But scientists still know little about how these relationships evolve or what spurs animals to grow specialized organs that encourage these symbioses.
Now Foster and an international team of researchers have mapped the genome of a Hawaiian bobtail squid, creating a new tool to explore these questions. By parsing the squid’s genome, the team has already discovered that the evolution of its light organ followed a completely different pathway than that of a second symbiotic organ, which supports reproduction. Published in the Proceedings of the National Academy of Sciences, the findings lay the groundwork for future studies of animal-microbe interactions, including those in humans.