Social costs are an underappreciated force for honest signalling in animal aggregations

Animals in social aggregations use signals of quality or motivation to attract mates and intimidate rivals. Theory indicates that honesty can be maintained in these signals if the costs of signalling affect low-quality individuals more than they affect high-quality individuals. Considerable research has focused on identifying the nature of those costs and their ability to maintain honest signals. Much of this research, particularly in recent years, has focused on receiver-independent physiological costs of signal production. Less research attention has been paid to receiver-dependent costs that might arise from conspecific responses to signals. Here we survey the literature on these different types of costs, focusing in particular on case studies from a diversity of taxa. We find that signals often do carry significant physiological production costs, but this is not universal, as many signals appear to be physiologically inexpensive to produce. More importantly, very few studies have tested the key prediction that physiological production costs differentially affect low-quality individuals over high-quality individuals. In contrast, research from a diversity of taxa indicates that signals such as coloration and vocalizations often affect agonistic interactions, which in turn affect the production of signals, and that deceptive signallers receive more aggression than do honest signallers in at least some systems. Social costs are a plausible but understudied mechanism for maintaining honest signalling. (C) 2017 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.