Reciprocal plasticity and the diversification of communication systems

The origin of novel communication systems has long been an evolutionary puzzle because communication requires interdependent signals and responses. Either component is not useful in isolation. Previous work has shown that novel communication systems may arise when pre-existing traits are co-opted for a novel function. However, research on developmental plasticity suggests we may benefit from considering how plasticity facilitates the origin and diversification of communication systems. In particular, plasticity can stabilize novel traits that are the first step towards signals or receiver responses (precursors) because plasticity allows individuals to rapidly adjust their phenotype based on their partner's phenotype, termed ‘reciprocal plasticity’. For example, exposure to a new sender precursor (e.g. new song) can produce a rapid, reciprocal change in receiver responses (e.g. preference for the new song). Reciprocal plasticity may facilitate the origin of new communication systems because precursors that influence conspecifics are more likely to become established signalling systems than precursors that are ignored by conspecifics. We review evidence that plasticity is important in the development and expression of a range of signals and preferences, the implications for divergence in signalling systems and its potential impacts on speciation and diversification. We outline areas of exciting future research, from incorporating more developmental realism into evolutionary models of signalling systems to using experimental evolution and novel anthropogenic environments to study genetic assimilation of plastic signals and preferences.