Q: In school, I have the assignment of putting together a report on how sponges communicate, and I can't seem to find any answers. The closest I have gotten is a scientific abstract that is too confusing for me to understand. So can you please tell me how sponges communicate? If not, can you please tell me where I might be able to get this information? Thanks a lot
A: What a great question. It's a pretty obvious question really, but most people don't think that sponges do anything they need to communicate about so they don't come up with it.
The short answer is that for the majority of sponges we don't know how they communicate. There are three groups of sponges. Two of which are cellular, that is are made up of lots of individual cells glued together by collagen and cell adhesion molecules and junctions, as we are. These are the demosponges and calcareous sponges. The third group, the hexactinellids, are syncytial. That means their cells are multinucleate, and in fact they are really really long strings of tissue, strung out like a spiders cobweb over the skeleton) with nuclei that truck around on pathways of microtubules, one of the the structural proteins of the cell that allow other molecules and proteins to move from one spot to another. OK. To communicate quickly i.e. electrically between cells you need to have an aqueous pathway, or a hole
between the cells. First, most cells are excitable themselves. If you stimulate them (poke them or apply current) the current will travel around the cell and activities in the cell will be affected. The membrane, however, acts as a good insulator stopping the current from going beyond. But, in
addition to nerves which are specialized for carrying ions (current=electrical signals), most animals have gap junctions. These act like a sieve for ions and allow a signal to pass from one cell to another.
The thing is that gap junctions haven't been found in sponges at all. They are known from the Cnidaria (jellyfish and anemones) up. So sponges that are cellular technically don't have a way to send a signal rapidly between the cells. But we do know that they can co-ordinate reproduction, as you said,
and some cringe if you touch them, though very slowly. What is likely happening in the first case is chemical communication. A hormone or something is given off by one sponge and picked up though the water it filters all through the body, and so all cells exposed receive the signal to release gametes. This doesn't have to be too quick. In the cringe response it's possible that there could be a mechanical or physical tweaking of one cell to the other, OR more likely there could be a calcium signal, passed
out though normal ion channels from one cell to the other. Calcium is used for slowish signalling in a number of animals (even in our brains by the glial cells) and could be used here, though no one has looked as it's quite a challenge.
Finally, the case of the hexactinellids is quite different. As they are syncytial their cytoplasm is all connected and there are no barriers, like the membrane, to electrical signalling. In fact if you touch a hexactinellid sponge it stops pumping water through the body right away. The response is electrical but is slower than the kind of signal that runs through nerves, mostly because the pathway is really circuitous (windy) and there could be fewer ion channels along the membrane, and likely there are fewer ions travelling in and out of the membrane each time the signal is reboosted as it travels along the sponge, all things that would slow it down. But none the less when something in the water touches a hexactinellid (perhaps a piece of dirt in the incurrent canals) an electrical signal travels through the whole sponge telling it to stop pumping. Why they have syncytial tissues, and why this ability to communicate electrically, a parallel system to nerves, evolved is another really interesting question we know nothing about. Hexactinellids would probably communicate chemically to reproduce like the demosponges, but again NOTHING is known about this at all.
If you want to visualize the structure of a hexactinellid I have a paper in the fall issue of Invertebrate Biology. And if you want to see a blurb on the electrical communication, we have a short communication in Nature, in the spring of 1997 (Leys, S.P. and Mackie, G.O., 1997. Electrical recording from a glass sponge. Nature 387:29-30).
Hope that helps.
Answered by Dr. Sally Leys