Eyespot (mimicry) - Evolution of The Eyespot at The Molecular Level

Evolution of The Eyespot At The Molecular Level

Butterfly eyespots are formed as a result of a morphogenetic signaling center, or organizer called the focus. This signaling center induces its neighboring cells to produce specific pigments which pattern the eyespot. Foci morphology and evolution appears to be the result of an altered regulatory circuit composed of the same patterning mechanisms conserved in insect wing patterning. This altered regulatory circuit is able to pattern both the anterior and posterior eyespots independent of the anterior/posterior wing compartmentalization restrictions.

Breaking the highly conserved compartmentalization restrictions put forth by insect wing patterning, by redeployment of early developmental signaling sources like the canonical hedgehog (Hh) pathway, Distalless (Dll), and engrailed (en), this altered regulatory circuit is able to pattern both the anterior and posterior eyespots independent of the A/P compartmentalization restrictions through increased localized levels of hh signaling. Increased hh signaling raises expression of its receptor ptc and transcription factor. Normally, in the fruit-fly Drosophila, engrailed(en) acts in the posterior compartment to restrict ptc and ci expression to the anterior compartment by repressing transcription of ci, thereby preventing expression of ptc. However, This rogue expression of ptc and ci seen in the posterior compartment of some butterfly wing disks, is an indication that during the evolution of eyespots, there was a divergence in the repression or expression of these genes from that of drosophila. From an evo-devo perspective, understanding the redeployment and plasticity of already existing regulatory mechanisms in butterfly eyespot loci development may give more insight into a fundamental mechanism for the evolution of novelty structures.