Colour pattern homology and evolution in Vanessa butterflies (Nymphalidae: Nymphalini): eyespot characters.

Abstract

Ocelli are serially repeated colour patterns on the wings of many butterflies. Eyespots are elaborate ocelli that function in predator avoidance and deterrence as well as in mate choice. A phylogenetic approach was used to study ocelli and eyespot evolution in Vanessa butterflies, a genus exhibiting diverse phenotypes among these serial homologs. Forty-four morphological characters based on eyespot number, arrangement, shape and the number of elements in each eyespot were defined and scored. Ocelli from eight wing cells on the dorsal and ventral surfaces of the forewing and hindwing were evaluated. The evolution of these characters was traced over a phylogeny of Vanessa based on 7750 DNA base pairs from 10 genes. Our reconstruction predicts that the ancestral Vanessa had 5 serially arranged ocelli on all four wing surfaces. The ancestral state on the dorsal forewing and ventral hindwing was ocelli arranged in two heterogeneous groups. On the dorsal hindwing, the ancestral state was either homogenous or ocelli arranged in two heterogeneous groups. On the ventral forewing, we determined that the ancestral state was organized into three heterogeneous groups. In Vanessa, almost all ocelli are individuated and capable of independent evolution relative to other colour patterns except for the ocelli in cells -1 and 0 on the dorsal and ventral forewings, which appear to be constrained to evolve in parallel. The genus Vanessa is a good model system for the study of serial homology and the interaction of selective forces with developmental architecture to produce diversity in butterfly colour patterns.