Colour pattern evolution and development in Vanessa butterflies

• Main Author: Abbasi, Roohollah
• Other Authors: Marcus, Jeffrey (Biological Sciences)
• Published: John Wiley & Sons Publishers 2015
• Subjects: Colour pattern evolution; Vanessa butterflies; Eyespot development; Butterfly wing; Drosophila; Compartment boundary; Mirror-image developmental organizer; Serial homology; Colour pattern development; Far-Posterior compartment boundary
• Online Access: http://hdl.handle.net/1993/30979

The evolution and development of eyespot and non-eyespot colour pattern elements was studied in Vanessa butterflies using a phylogenetic approach. A Bayesian phylogeny of the genus Vanessa was reconstructed from 7750 DNA base pairs from 10 genes. Twenty-four non-eyespot and forty-four eyespot color pattern elements from the Nymphalid ground plan were defined and studied and their evolutionary history was traced on the Vanessa phylogeny. Ancestral character states were predicted and the direction of evolutionary changes was inferred for all characters. Five serially arranged eyespots were predicted for the ancestral Vanessa on all wing surfaces. Homologous eyespot and non-eyespot characters on the surfaces of the forewing were more similar than those on the surfaces of the hindwing. Homologous eyespot characters on the dorsal surfaces of fore and hindwings show more similarities than the ventral surfaces, in contrast to what was found for non-eyespot characters. Independent Contrast analysis was also used to study correlations between eyespot characters. Independent Contrast analysis revealed significant correlations between eyespots 2 and 5 and eyespots 3 and 4 on all wing surfaces. This consistency among highly variable eyespot characters suggested a structural hypothesis: the existence of a Far-Posterior (F-P) compartment boundary and organizer could be responsible for the observed correlations. This hypothesis was tested in several ways. First, examination of wing patterns across species from all families of butterflies revealed correspondence between wing cells 1 and 4 and between cells 2 and 3. Second, evaluation of spontaneous mitotic clones in butterflies and moths reveals a peak abundance of clonal boundaries along the vein dividing wing cells 2 and 3. Finally, experimentally generated FLP/FRT mitotic wing clones produced in Drosophila, reveal a clonal boundary posterior to the L5 wing vein, which is homologous to the vein dividing wing cells 3 and 4 in butterflies. Collectively, this suggests the existence of an additional compartment boundary associated with an organizer in wing cell 3 responsible for patterning the posterior portion of insect wings. A model is proposed that predicts that the wing developmental compartment boundaries produce unique combinations of gene expression for each wing sector, permitting eyespot individuation. === February 2016