Spots and stripes: the evolution of repetition in visual signal form.

It is common to find spatially repetitive patterns in animal visual signals. The evolution of such patterns is not well explained by existing theories of signal evolution. In this paper, we suggest that the evolution of signals with spatial repetition may be due to specific recognition problems and receiver biases. The logics of our hypotheses are studied in co-evolutionary simulations using artificial neural networks as models of receivers. These simulations yield repetitive visual signals under the following conditions: translations and reflections of the signal, partial obstruction of the signal, a fixed feature in the signal, and lateral inhibition in the receiver. In addition to regular repetitions our simulations sometimes result in other organisations of the signal such as blocky patterns and gradients.