Eyespot (mimicry)
The pattern-forming biological process (morphogenesis) of eyespots in a wide variety of animals is controlled by a small number of genes active in embryonic development, including the genes called Engrailed, Distal-less, Hedgehog, Antennapedia, and the Notch signaling pathway.
The eye-like markings in some butterflies and moths and certain other insects, as well as birds like the sunbittern, serve functions in addition to mimicry;[1] indeed, it is unclear whether they actually mimic eyes.
[2] There is evidence that eyespots in butterflies are antipredator adaptations, either in deimatic displays to intimidate predators, or to deflect attacks away from vital body parts.
[3][4] In species such as Hipparchia semele, the conspicuous eyespots are hidden at rest to decrease detectability, and only exposed when they believe potential predators are nearby.
[5] Butterflies such as the blues (Lycaenidae) have filamentous "tails" at the ends of their wings and nearby patterns of markings, which combine to create a "false head".
[13][14] Male birds of some species, such as the peacock, have conspicuous eyespots in their plumage, used to signal their quality to sexually selecting females.
[15][16] Several species of pygmy owl bear false eyes on the back of the head, misleading predators into reacting as though they were the subject of an aggressive stare.
[21] Butterfly eyespots are formed during embryogenesis as a result of a morphogenetic signalling centre or organizer, called the focus.
These genes are the transcription factor Distalless (Dll) and the ligand (a signalling substance that binds a cell surface receptor) Hedgehog (Hh).
[25] Butterfly eyespot morphology appears to be the result of the evolution of an altered version of the regulatory circuit which patterns the wings of other insects.
This rogue regulatory circuit is able to pattern both the anterior and posterior eyespots independent of the usual anterior/posterior wing compartmentalization restrictions seen in the fruit fly Drosophila.
The second domain starts around 20 hours after pupation around the original central cluster of cells, in an area in which a black ring of the eyespot will be formed.
Functional experiments using transgenic Bicyclus anynana (the squinting bush brown butterfly) have shown that overexpression or down-regulation of Dll in the first expression domain correlates with bigger and smaller eyespots respectively.
However, if this is done on the second domain then the overall size of the eyespots remains the same, but the width of the black ring raises with a higher amount of Dll.
The study authors, Cameron Radford and colleagues, note that in the Sundarbans, forest users wear face masks with eye markings on the backs of their heads in the hope of reducing tiger attacks.
