In a paper published online in Nature Communications, scientists detail how colonial siphonophores – gelatinous planktonic organisms related to jellyfish, anemones and corals – swim by coordinating multiple water-shooting jets from separate but genetically identical units that make up the organism.
The physonect siphonophore Nanomia bijuga. Image credit: John H. Costello et al.
Siphonophores have the most complex colony-level organization of any animal.
One such species, the physonect siphonophore Nanomia bijuga, is a predatory organism made up of a number of specialized individuals, called zooids, that each work together to survive.
At the front of the colony are a series of genetically identical zooids called nectophores, which make up the propulsive engine of the organism known as the nectosome, operating like jets by pumping water backwards. Towed behind this are the zooids that specialize in reproduction and feeding.
To analyze how exactly this multi-jet propulsion system works, the scientists videotaped Nanomia bijuga off of Friday Harbor, Washington.
They discovered that the younger, smaller nectophores growing at the front maneuver the colony use their jets to influence its direction.
In contrast, the older, larger nectophores provide forward or reverse thrust to propel the colony during its daily migration.
Nanomia bijuga body structure: the propulsive component of the colony consists of the nectophores that bud sequentially (numbered in order of their origin) from a budding zone near the pneumatophore float at the anterior region of the nectosome; nectophores lie in one plane bisected by the nectosomal axis; the siphosome includes the feeding and reproductive members of the siphonophore colony. Image credit: John H. Costello et al.
“It’s a quite sophisticated design, for what would seem like a simple arrangement,” said the study’s lead author Dr John Costello of the Marine Biological Laboratory and Providence College.
“The young members have what we call a long lever arm. They are like the handle of a door. If you push on a door near its hinges – its axis of rotation – the door is hard to open.”
“But if you push on the door handle, which is far from the axis of rotation, the door opens easily. A little force placed with a big lever arm has a big effect on turning.”
This pattern ensures that all members of the colony, young and old, perform important tasks and their developmental organization allows for cooperation.
Dr Costello and his colleagues suggest that this simple and efficient means of multi-engine organization could influence the design of underwater propulsion vehicles.
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John H. Costello et al. 2015. Multi-jet propulsion organized by clonal development in a colonial siphonophore. Nature Communications 6, article number: 8158; doi: 10.1038/ncomms9158
