Résumé
Mimetic resemblance in unpalatable butterflies has been studied by
evolutionary biologists for over a century, but has largely focused on the
convergence in wing color patterns. In Heliconius numata, discrete
color-pattern morphs closely resemble co-mimics in the distantly-related
genus Melinaea. We examine the possibility that the shape of the butterfly
wing also shows adaptive convergence. First, simple measures of forewing
dimensions were taken of individuals in a cross between H. numata morphs,
and showed quantitative differences between two of the segregating morphs,
F. elegans and F. silvana. Second, landmark-based geometric morphometric
and elliptical Fourier outline analyses were used to more fully
characterize these shape differences. Extension of these techniques to
specimens from natural populations suggested that, while many of the
coexisting morphs could not be discriminated by shape, the differences we
identified between F. elegans and F. silvana hold in the wild.
Interestingly, despite extensive overlap, the shape variation between
these two morphs is paralleled in their respective Melinaea co-mimics. Our
study therefore suggests that wing-shape variation is associated with
mimetic resemblance, and raises the intriguing possibility that the
supergene responsible for controlling the major switch in color pattern
between morphs also contributes to wing shape differences in H. numata.