Fig 1. Extensive form of the signalling game.

S1, S2 and R1, R2 denote the decisions the signaller and the receiver have to make respectively; S1: ASD stage, give or not to give an ASD; R1: search stage: search or not to search for ASDs; S2: quality signalling stage: give or not to give a quality signal; R2: decision stage: give or not to give the resource to the signaller. R and S(H) denote receiver and high quality signaller respectively. For the sake of simplicity the tree does not show the decision made by nature, i.e. the step that specifies the quality of signaller, it only shows the game for high quality signallers. The same decision tree can be drawn for low quality signallers. Dotted arrows denote the nodes where the receiver cannot tell whether the node is part of the first or the second tree, i.e. where the receiver cannot tell whether the signal (or lack of it) comes from a high or a from a low quality signaller. Table 2 gives the fitness values corresponding to the end nodes.