Characteristic patterns on a wing are the result of the wing shape, the mapping of the wing venation, and the actual shape size and coloration of pattern elements formed by the scale cells. There are several studied processes that are responsible for modifying the generic pattern elements found in the Nymphalid ground plan into the spectacular diversity we have come to expect from these inspirational insect designers. Each individual wing cell (the space between the wing veins) are capable of customizing the pattern elements found within. This kind of cell-by-cell customization gives the freedom to resize, shape and color individual elements. An additional mechanism worth noting is known as pierellization where pattern elements become so dislocated from their expected neighboring wing cell element that they align to other elements. This freedom of pattern manipulation has allowed species like the Indian Leaf Butterfly to simulate a very convincing leaf pattern on the ventral wing surfaces, complete with venation that mimics a leaf rather that a butterfly wing.
Many adaptational and morphological observations can be made from the study of butterfly wing patterns including mimicry, polymorphism, polyphenism, and dimorphism. A couple of mimicry systems are observed in butterfly wing designs. Batesian mimicry is defined by a tasty butterfly resembling a well know distasteful species. In this case, a few butterflies gain the associative protection of mimicking the Monarch butterfly`s orange and black striped pattern. Mоllerian mimicry is where a group of distasteful butterfly species have evolved to all look alike thus increasing the chances of recognition that a particular design and coloration scheme represents bad meal. Polymorphism the genetic code of a single species is capable of a couple of distinctly different looking adults. This characteristic is typically found in tropical butterflies. Polyphenism is defined by genetically identical caterpillars producing pattern variations in the adults due to environmental triggers such as the length of the day (season), temperature, or the relative availability of water. Dimorphism is where genetic differences between males and females result in differing color patterns for each gender.
In a few cases, specific butterfly patterns are more readily associated with functional advantages. The dorsal patternation of butterflies function as gender signals, allowing mates to recognize one another. Advertising your unpaletable nature through bold aposematic (warning) coloration, successfully establishes a learned avoidance response from predators. Camouflage and cryptic coloration have the obvious advantage of rendering the butterfly harder to find. Eyespots (ocelli) flashed as an otherwise cryptic butterfly makes a hasty retreat, can confuse an attacker or at least help to focus the attack towards non-critical regions of the body. Melanization is a useful device employed by some butterflies and moths. Forms that have extra black (melanized) scales are better equipped to absorb heat from the sun and thus thermoregulate themselves to activity in cooler climates. Many other design and wing structure advantages have been studied but his sampling should give you an idea that many designs amount to considerably more than an aesthetically pleasing set of wings. From a developmental perspective, the formation of a butterfly wing pattern is the result of a complex coordination of processes, timing and genetics. The mechanics that determine the ground scales (background), pigmentation, pattern element size, shape, position, and symmetry, ultimately determine the pattern. Experiments have revealed pattern determination is established and finalized within the first few days after the caterpillar enters its pupal stage. At this time, the wing views, the wing shape, the epidermal membrane, pattern elements and coloration are determined. At the root of the pattern development mechanism is the diffusion of a morphogenic substance through the epidermal layers. These diffusions, controlled by activating and inhibiting enzymes, result in gradients of the morphogenic substance. Reaction thresholds based on the concentration of the morphogen determine the contours of the actual pattern elements. Some pattern elements are formed from the source position of the morphogen while others are initiated by the absence of the morphogen (concentration sink). The exact pattern shapes are usually formed from the contours generated from the addition of multiple morphogen gradient sources or inhibitions. Controlled by genetic and environmental factors, the final pattern might best be described as a developmental freeze-frame at the beginning of pupal stage when the pattern finalized.