Individual selection, kin selection, and the shifting balance in the evolution of warning colours: the evidence from butterflies

It is difficult to imagine how warning colours evolve in unpalatable prey. Firstly, novel warningly coloured variants gain no protection from their colours, since predators have not previously encountered and learnt their colour patterns. This leads to a frequency-dependent disadvantage of a rare variant within a species. Secondly, novel warningly coloured variants may be more conspicuous than non-aposematic prey. Nevertheless, it is obvious that many palatable butterflies have bright colours used in intraspecific communication and in duping predators. Other palatable butterflies are already warningly coloured. Should such butterflies evolve unpalatability, perhaps because of a host-plant shift, these bright colours would be preadapted to a warning role. Warning colours could then continue to evolve by enhancement of memorable characteristics of these patterns, or by mimicry. Even within lineages of warningly coloured, unpalatable butterflies, colour patterns have continued to evolve rapidly. This diversity of warning colour patterns could have evolved in a number of ways, including individual and kin selection, and by the shifting balance. Evidence for these mechanisms is discussed, as are the similarities between the evolution of warning colours and more general evolutionary processes, including sexual selection and speciation.