Colour Patterns on Buttrfly Wings.
Introduction
The vibrant color patterns on butterfly wings result from both pigments and structural features. Some colors are produced by light-absorbing chemicals, while others, like brilliant blues, come from microscopic scales that reflect light. These patterns have evolved for various purposes, such as attracting mates and camouflage. In this blog, we'll explore the science behind butterfly wing patterns, revealing how biology and physics work together to create these stunning displays
- A German Entomologist, Naturalist & Scientific illustrator, named Maria Sibylla first observed that butterflies develop from cattrerpillars.
- All butterflies and moths belong to the order Lepidoptera, which literally means "Scaled wings" in Greek.
Colour pattern in wings of the Butterflies
- The colour pattern of wings are formed from a mosaic of scale cells containing pigments, called Symmetry system
- With the colouration cause by the reflection of light with particular wavelengths by ridges found on scale surfaces.
The Symmetry system
- In the Symmetry system, there are a pair of pigment bands, that run parallel to each other from the anterior to the posterior margin of the wings.
- There are three symmetry systems that make up the basic wing patterns of the butterflies.
- The basal symmetry system,
- The central symmetry system, and
- The border symmetry system.
- There may be one or two narrow bands that run closely parallel to the distal wing margin known as Submarginal bands.
- Along the middle of the border, a cntral symmetry system is present with distinctive set of pigment marks.
- The border symmetry system are highly elaborated into eyespots and are called border ocelli.
- Each pigment band is interrupted whenever it crosses a wing vein, the reason why it looks like a linear series of short segments.
Fig.: The vertical structure of ground plan and it's constitutive symmetry system
Fig.: The wing veins, breaking up the bands of symmetry system into semi-independent pattern.
The ground plan of the symmetry system consists of 8 parallel series of pattern elements, one for each band in each symmetry system- a row of border ocelli and a set of submarginal bands.
Fig.: Border ocelli an Submarginal bands.
Structures, that produce colouration
- The colour producing structures present in the wings of butterflies are the scale cells, the modification of epithelial cells of the wings.
Fig.: Scanning Electron Microscope image of an isolated ground scale showing ridges and cross ribs.
Common pigments, that cause the colouration
- Melanin: Grey, Black & Bronwn.
- Ommachrome: Red, Orange & Tan.
- Pterin: Orange.
- Papiliochrome: Yellow & Creme.
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Genes, that control colour pattern
- These genes encode some proteins that lead to varied colouration in their wings.
- These genes are of two sets-
- Some cause the colouration.
- Other control the pigment making pathway by switching on or off.
Studies have been done on the genetic basis of colour variation of two genera, Heliconius & Papilio.
Optix
- These are the factors and are responsible for turning on and off in most Red, Orange, and Brown colour patterns in H. erato, H. melpomene and H. cyndo.
H. erato Image Source
H. melpomene Image Source
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H. cyndo Image Source
Cortex
- It belongs to a family of cell cycle regulator, that can control the scale cell colour through controlling melanin pigmentation in the peppered moth, by the insertion of the transposable elements.
- The Cortex gene actually functions as a Cis-regulatory gene rather than directly controlling the colouration of the wings.
- Cortex has seveeral 5' Untranslated Exons (UTRs) of over 100kb.
Wnt A
- It controls several aspects of the size and shape of the colour elements.
- It also controls the colour pattern differences between Batesian mimetic and Non-Batesian populations of the admiral butterfly.
- Its locus is not as cleaer as of the previous two.
Fig. : Batesian Mimicry : Image source
Chromosome 13
- It controls the shape of colour bands on forewings in H. erato & H. melpomene.
K locus in Chromosome 1
- It controls a switch between yellow and white in H. melpomene & H. cyndo.
- The exact gene in this locus is unknown yet.
Significance of Colour Patterns on Butterfly Wings
Camouflage
- The wing patterns and colours help the butterflies to blend into their surroundings to avoid threats.
Warning Signals
- bright and vibrant colours on butterfly wings can act as warning signals to predators, indicating that the butterfly is toxic or unpalatable. This behaviour is known as aposematism.
Mate Attraction
- Butterfly wing colouration plays a vital role in courtship behaviour, where males display colourful & intricate wing patterns with some visual striking features to attract females.
Thermoregulation
- The colouration of butterfly wings can impact their ability to regulate body temperature.
- Darker colours can absorb more heat, which aid the butterflies in surviving in cooler climates and in the time when they need to warm-up their flight muscles.
- Conversely, light colours reflect more sunlight & heat, helping them to stay cool in hot environment.
Species Identification
- Each butterfly species often has unique wing patterns and colours, aiding in species recognition for mating, foraging and other behaviours.
Communication
- Butterfly wing colours can serve as a form of communicaton between individuals of the same species.
- Some species engage in territorial display or interaction using their wing patterns and colour to convey dominance or submission.
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