The structures of vertebrate chemosignals reflect their functions and the environment they are used in. Temporal parameters, spatial range, localizability, intensity, detectability, and information content of the signal depend on both the chemical structure and the operating environment (Alberts, 1992a). The chemical properties involved include functional groups of the molecule; volatility; aromaticity; the number of compounds composing the entire signal; and when, where, and how it is emitted (Alberts, 1992b).

Functional groups

Functional groups can determine communicative activity of a molecule. For example, hypoxanthine 3N-oxide triggers alarm responses in Ostariophysan fish. The amineoxide (NO) functional group (Fig. 2.1) appears to be essential for the antipredator behavior of fathead minnows, Pimephales promelas, and finescale dace, Phoxinus neogaeus (Cyprinidae) to occur. Structurally similar molecules lacking the NO group did not release alarm responses in two tetra species (Charicidae). All four species belong to the Ostariophysi, and the response to the NO group is probably widespread in this order, also known as Cypriniformes (Brown et al., 2000).