The diversity in colour patterns on butterfly wings provides great potential for
understanding how developmental mechanisms may be modulated in the evolution
of adaptive traits. In particular, we discuss concentric eyespot patterns, which
have been shown by surgical experiments to be formed in response to signals
from a central focus. Seasonal polyphenism shows how alternate phenotypes can
develop through environmental sensitivity mediated by ecdysteroid hormones,
whereas artificial selection and single gene mutants demonstrate genetic variation
influencing the number, shape, size, position, and colour composition of the eyespots.
The expression patterns of the regulatory gene Distal-less reveal that these
changes can arise at several different developmental stages, and the phenotypes
indicate that some forms of changed pattern may occur much more readily than
others. Further study of the genes, of the developmental mechanisms, and of the
functions of the patterns will provide novel insights about the evolution of morphological
diversity