Visual and Chemical Signalling in Butterflies: Functional and Phylogenetic Perspectives

The two major signal functions for adult butterflies are protection against predators and intraspecific communication. Protective use of colour patterns (e.g. aposematism, crypsis) is mainly directed against visually hunting vertebrate predators. Mate location in butterflies is effected through behavioural adaptations of both sexes, and long-range visual searching by males. Recognition and selection of mates at close-range is largely controlled by species-specific male pheromone components, although other signals (e.g. colour, movement) play the initial role. Increased elaboration of pheromones for specific signalling has been hypothesized where the design of visual signals is constrained by defensive functions involving pattern convergence (co-mimicry). Male pheromones are also important for trait signalling, often being decisive in female mate choice. The general context of visual and olfactory signals in butterfly communication is discussed using specific examples, including Amauris. Their low divergence in colour patterns contrasts with great differentiation in the chemistry of their scent-organ volatiles. Models for the evolution of chemical signalling systems in these mimetic butterflies are compared and assessed. A more complete understanding of the evolution and function of butterfly signalling systems will require renewed effort in a number of areas. These include integrated studies on the use and significance of colours and scents, the measurement of colour, chemical analyses of pheromone bouquets, genetics, and receptor physiology. All of this work will need to be put in a better comparative framework through cladistic analysis of a wider variety of biologically contrasted butterfly groups, including previously studied case lacking a rigorous phylogenetic perspective.