Photonic Structures in the Animal Kingdom: Valuable Inspirations for Biomimetic Applications - Biomimetic Architectures by Plasma Processing - page 24

1.8.1 Sex Recognition and Mate Choice

Another important function of colouration is sex recognition,
especially since many animals show a strong sexual dichromatism,
that is, the colouration of males and females of the same species
differs. In many butterfly species, for example, specifically the males
exhibit iridescent colouration, whereas the females are pigmentary
coloured. Therefore, to achieve recognition by mates, a unique
optical signature has to be displayed by the animal, and conspecifics
must be able to recognise members of their own species by the
colouration and/or changes thereof.
The UV reflectance is also a means of communication channel
based on nanosised structures. Well-studied examples are the pierid
butterflies that show strong variations in their optical signature,
that is, their UV reflectance and their pigmentation, within a group
of closely related butterflies [13]. Polarised light also offers an
important sex recognition channel. In two

butterflies,
it has been shown that potential mates are recognised by their
(presence or lack of) polarised iridescence [64]. Also, the metallic
elytra of

Heliconius

reflect light strongly polarised under high
incidence angles, hence serves as a mate recognition signal [27].
The colourful displays further play a role in the mate choice. In
studies with UV-reflecting pierid butterflies, males with a higher UV
reflectance had a higher copulation success than males with a lower
UV signal [65]. Similarly, the number of iridescent eye spots in the
peacock tail feathers is important for the mating success [66]. An
intriguing question is, whether the visual system of animals with
iridescent displays has undergone convergent evolution with the
displayed colouration?

C. fulgidissima

1.8.2 Warning Colouration

Colouration is often used to warn predators of the potential unpalat-
ability and toxicity of the potential prey, for example, by displaying
special wing patterns [67]. This so-called aposematic or warning
colouration, once evolved, initiated mimicking the colouration of
toxic species by non-toxic conspecifics, leading to convergent evolu-
tion of specific colouration pattern in mimicry rings [68]. A particu-
larly well-studied example is the butterfly genus Heliconius , where