Colonies of highly mobile, jellyfish-like organisms, called physonect siphonophores, are powerfully propelled through the oceans by older colony members, while younger individuals up front provide the steering, reports a study in Nature Communications. This division of labour among different developmental stages is thought to be key to the colonies’ success.
Siphonophores - gelatinous planktonic organisms related to jellyfish, anemones and corals - have the most complex colony-level organisation of any animal. One such species, Nanomia bijuga, is a voracious predator made up of a number of specialised 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 are specialised for reproduction and feeding.
John Costello and colleagues use image tracking to investigate how exactly this multi-jet propulsion system works in N. bijuga and discover that the younger, smaller nectophores growing at the front manoeuvre the colony using 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. This pattern ensures that all members of the colony, young and old, perform important tasks and their developmental organisation allows for cooperation. The authors suggest that this simple and efficient means of multi-engine organisation could influence the design of underwater propulsion vehicles.