Portuguese Man-of-War: A Strange Case

Most of us are familiar with the Portuguese man-of-war (Physalia physalis) because of the painful sting that its tentacles deliver.

But the man-of-war has a hidden secret. It is easy to think of it as a very treacherous jellyfish. But it is not a jellyfish at all. It is much more. The man-of-war is an animal which consists of a colony of different types of specialized organisms. These organisms are involved in a set of complex and mutually beneficial symbiotic relationships with each other.

man-of-warThe organisms which make up the Portuguese man-of-war are comprised of four different types of polyps:

A single polyp makes up the gas-filled bladder known as a pneumatophore, which can be seen above the water. Unlike jellyfish which contract their bell to create a jet of water as a means of propulsion, the man-of-war is at the mercy of the wind and current as the bladder acts as a type of sail.

The man-of-war can temporarily deflate its floating bladder and sink below the surface to avoid bad weather or predators from above.

The next  group of organisms make up the tentacles. These tendrils can grow to a maximum length of 55 yards, and are equipped with venom filled nematocysts which paralyze or kill their prey. These structures also serve to keep predators away. The sting of the man-of-war can be agonizingly painful for humans, but is seldom fatal.

After prey is caught, tentacles pull the victim to the gastrozoids which are a third type of polyp, responsible for digestion.

A fourth group of organisms called gonozooids form the structures needed for reproduction. If I understand the process correctly, the gonozooids of each man-of-war releases either sperm or eggs into the open ocean. When the sperm from one man-of-war meets with the egg of another, the egg is fertilized. Then each newly formed organism goes through a process called budding which is an asexual form of reproduction. The resulting “buds” develop into a member of the colony with a specific task. Each organism plays its role as part of a very unique creature called the man-of-war.

One has to marvel at the high degree of organization and mutualistic cooperation which exists between the organisms which make up the man-of war. But does the man-of-war really fit our definition of symbiotic mutualism?

Beyond a doubt, the organisms display a gained benefit between individuals. However, our definition limits the interactions of mutualistic partners to those which exist between different species of biological organisms. The man-of-war itself is a species, and the polyps are all offspring of a single organism through budding. Wouldn’t that mean the polyps would just be considered building blocks which make up organs of the man-of-war?

I don’t know if science has an answer for this, or if it is a gray area. But polyps of the Portuguese man-of-war possess the spirit of mutualism, if not the precise definition. I don’t know about you, but I am willing to stretch the definition of mutualism a bit to include these amazing sea creatures.