Blending of animal colour patterns by hybridization

Biologists have long been fascinated by the amazing diversity of animal colour patterns. Despite much interest, the underlying evolutionary and developmental mechanisms contributing to their rich variety remain largely unknown, especially the vivid and complex colour patterns seen in vertebrates. Here, we show that complex and camoufl aged animal markings can be formed by the ‘ blending ’ of simple colour patterns. A mathematical model predicts that crossing between animals having inverted spot patterns (for example, ‘ light spots on a dark background ’ and ‘ dark spots on a light background ’ ) will necessarily result in hybrid offspring that have camoufl aged labyrinthine patterns as ‘ blended ’ intermediate phenotypes. We confi rmed the broad applicability of the model prediction by empirical examination of natural and artifi cial hybrids of salmonid fi sh. Our results suggest an unexplored evolutionary process by means of ‘ pattern blending ’ , as one of the possible mechanisms underlying colour pattern diversity and hybrid speciation.