Marler rejects the notion that a mouse rustling in the grass is communicating to an owl that is hunting it. Clearly there has been selection for the concealment of the mouse, but also for detection by the owl. Krebs and Dawkins went as far as to suggest that animal communication is really nothing more than one animal trying to manipulate another with signals evolving to this end. This probably goes too far. Animals may coordinate activities without apparent signal.
Air breathing tropical freshwater fish a good example.
Low oxygen in ponds, high risk of predation on surface, reduce risk by synchronously breathing. This is a kind of social facilitation. We may not be able to detect the signals that are used. Meaning is what the recipient makes of the message. This can only be inferred from changes in the behavior of the recipient.