by Leslie Kent
Many animals use camouflage to disguise themselves to increase their chance of survival or to have an advantage over prey. There are many examples of camouflage that you’re probably familiar with, such as chameleons that change color to match their surroundings, bugs that look like leaves or sticks, and arctic animals that have white coats to blend in with snow. These are all examples of cryptic coloration, which is a camouflage tactic where organisms’ color or markings enhance their ability to blend into their environment. However, there are other types of camouflage that you may not have heard of before.
The bobtail squid has a really interesting camouflage system. Bobtail squids live in shallow areas of the ocean. They are nocturnal, which means they spend their days asleep burrowed in the sand and at night they are awake hunting their prey. While searching for food, they need to avoid predators to survive. The problem is that predators of the bobtail squid use shadows created by moonlight and starlight to find bobtail squids. To hide from their predators, bobtail squids have evolved a mutually beneficial relationship with a species of bacteria named Aliivibrio fischeri (formerly called Vibrio fischeri).
Hawaiian Bobtail Squid (Courtesy of NSF, Credit: Chris Frazee/University of Wisconsin School of Medicine and Public Health)
A. fischeri is a type of bacteria with a special ability: they are bioluminescent, or able to make their own light. This process is the result of quorum sensing, which is when a population of bacteria can sense neighboring bacterial cells and then all the cells act similarly. In the case of A. fischeri, when they are dense enough they turn on genes that make light.
Bioluminescent A. fischeri (Courtesy of NSF, Credit: J. W. Hastings, Harvard University, through E. G. Ruby, University of Hawaii)
Bobtail squids have a light organ in which they provide an environment for A. fischeri to grow and produce light. The light organ is able to sense how bright the light is from above, and then adjust how much light shines through the light organ to make the bobtail squid hard to see from below. This type of camouflage is called counter-illumination. While some animals produce their own light for counter-illumination, such as the hatchetfish, bobtail squids can’t and therefore have to rely on bacteria to help them survive.
In exchange for the important job A. fischeri does for the bobtail squid, the bacteria are provided with food and a safe place to grow. These two organisms form a mutually beneficial interaction where they protect each other. Together, they better their chances of surviving.
