Body postures and patterns as amplifiers of physical condition

The question of why receivers accept a selfish signaller's message as relia ble or 'honest' has fuelled ample controversy in discussions of communicati on. The handicap mechanism is now widely accepted as a potent constraint on cheating. Handicap signals are deemed reliable by their costs: signallers must choose between investing in the signal or in other aspects of fitness. Accordingly, resources allocated to the signal came to reflect the signall er's fitness budget and, on average, cheating is uneconomic. However, that signals may also be deemed reliable by their design, regardless of costs, i s not widely appreciated. Here we briefly describe indices and amplifiers, reliable signals that may be essentially cost free. Indices are reliable be cause they bear a direct association with the signalled quality rather than costs. Amplifiers do not directly provide information about signaller qual ity, but they facilitate assessment by increasing the apparency of pre-exis ting cues and signals that are associated with quality. We present results of experiments involving a jumping spider (Plexippus paykulli) to illustrat e how amplifiers can facilitate assessment of cues associated with physical condition without invoking the costs required for handicap signalling.