Sponges build their skeletons in a way that resembles the construction of human-made buildings - but without the architectural plans, a new study has found.
"We were surprised to find that spicules are dynamically moved and then become held up; we were very fascinated," said Noriko Funayama of Kyoto University in Japan.
Spicules' needle-like forms of silica have long been known as the structural supports found in the bodies of sponges. While the skeletons of sponges do have clear similarities to architectural buildings, no one knew how they were put together in development.
Funayama and her colleagues have now captured movies of the developing freshwater demosponge Ephydatia fluviatilis that show how those spicules are produced, transported, and assembled by a cast of "player cells" to prop up the sponges' bodies and support their growth.
First, spicules are produced by one type of manufacturing cell. Second, transporter cells carry mature spicules until they pierce the outer surface of the animal.
At that point, the pierced spicule is raised up and its basal end cemented in place with collagen matrices to form a basic pole-and-beam structure.
In other words, there is a division of labour among various types of cells within the sponges, which produce the self-organised biological structures through a chain of simple reactions.
The findings show a fundamentally new mechanism of forming the three-dimensional body shape of animals, the researchers said.
"So far as we know, this is the first report of collective behaviours of individual cells building a self-organised biological structure using non-cellular materials - a parallel to, for example, the well-known collective behaviors of individual termites building mounds," Funayama said.
The researchers now plan to examine skeletal construction in other species of sponges.
"This work not only sheds new light on skeleton formation of animals, but also might inspire interdisciplinary studies in fields such as theoretical biology, bioengineering, robotics, and architectural engineering, utilising mechanisms of self-constructing architectures that self-adjust to their environments, including remote environments such as the deep sea or space," the researchers said.
The study was published in the journal Current Biology.
