Color-pattern modifications and speciation in butterflies of the genus Vanessa and its related genera Cynthia and Bassaris

We have previously shown that the systemic injection of sodium tungstate, a protein-tyrosine phosphatase (PTPase) inhibitor, to pupae immediately after pupation efficiently produces characteristic color-pattern modifications on the wings of many species of butterflies including Vanessa indica and Cynthia cardui. In these species, the black spots reduced in size in response to the treatment. Similar modifications are occasionally seen in the field-caught aberrant individuals. Exceptionally, however, a C. cardui individual with enlarged black spots ("reversed" modification pattern) has been reported. Here we show that these modified patterns of V. indica and C. cardui are quite similar to the normal color-patterns of other Vanessa species. V. indica with tungstate-induced modifications resembled V. tameamea, V. samani, and Bassaris itea, whereas V. dilecta, V. atalanta, and V. dejeanii are similar to the "reversed" individual. Most features seen in the experimentally-modified V. indica were observed throughout the fore- and hindwings of V. samani. In contrast, the experimentally-induced color-patterns of C. cardui did not parallel variation of Cynthia butterflies. Since it has been proposed that a hypothetical transduction pathway with a PTPase for the scale-cell differentiation globally coordinates the wing-wide color-patterns, our findings suggest that spontaneous mutations in genes in this hypothetical pathway might have played a major role in creating new color-patterns and species in the Vanessa genus but not in the Cynthia genus. This evolutionary mechanism may probably be shared more widely in Lepidoptera, although this would not be a sole determinant for the color-pattern development and evolution.