Colourful and beautifully patterned; the wings of butterflies might call to mind similar descriptive phrases. These elegant wings have intrigued one group of scientists from NUS Biological Sciences to take a closer look at the genetic scaffolding that affect their appearance. Led by Associate Professor Antonia Monteiro and her PhD student Anupama Prakash, the scientists identified a gene — apterous A — that impacts the appearance of the dorsal wing surfaces of the African squinting bush brown butterfly, Bicyclus anynana.
The two surfaces of a butterfly’s wings — dorsal (top) and ventral (underside) — can have distinct patterns and colours which have evolved from the divergent functions of each surface.
“As butterflies sit with their wings folded, the exposed ventral surfaces usually help to camouflage them from predators. On the other hand, the hidden dorsal surfaces have bright colours to attract potential mates. However, the mechanisms involved in the development of these distinct differences in butterfly wing patterns are not clear,” explained Assoc Prof Monteiro.
The research team hypothesised that the gene apterous A could be involved in differentiating the appearance of the two wing surfaces. This gene is known to play a role in the wing development of some insect species such as the fruit fly, and is important in functions such as wing growth and determination of the boundary between the dorsal and ventral surfaces.
To verify the functions of this gene in wing development and patterning, the biologists investigated the expression of apterous A in the wings of the African squinting bush brown butterfly and then selectively removed it from the genome in a gene knockout process.
apterous A was found to be expressed solely on the dorsal wing surfaces and when it was removed from the genome, some butterflies experienced mutations and defects in wing development, shared Anupama.
“When this gene is mutated, the dorsal wing patterns of butterflies with the mutated genome develop the same patterns as their ventral wing surfaces,” she added.
apterous A is thus not only necessary for the development of butterfly wings but is also a key factor in determining the different patterning of each dorsal wing surface.
Their studies also revealed that this multifunctional gene is involved in the development of other features such as eyespot patterns — markings resembling an eye — and sex-specific traits found on the dorsal wing surface.
When the gene was deleted, multiple additional eyespots developed on these dorsal wing surfaces — as many as the number present on the ventral surfaces.
“In the evolution of butterfly wing patterns, eyespots appeared on the dorsal wing surfaces of butterflies long after their origin on the ventral surfaces, but the reason for this was unclear,” said Assoc Prof Monteiro.
Their study gave some clarity to this, revealing that areas where eyespot patterns appeared on the dorsal wings were also where there was an absence of apterous A, implying that the gene acts as a repressor of these traits.
The presence of apterous A also had an effect on the sex-specific wing traits on the dorsal surfaces. The researchers observed that the gene acted as either a repressor or activator of various male-specific wing traits found on both the fore- and hindwings of the dorsal surfaces, such as pheromone-producing organs and silver scales.
“This study has identified a gene that influences surface-specific wing patterns in butterflies. This can potentially be used as a biomarker to understand how specific cells produce the different colours and patterns that we see on butterfly wings,” said Anupama.
“Since apterous A is expressed only in cells of the dorsal surface, we can now identify dorsal-specific cells based on this gene expression. This is very useful if, for example, we want to study how a certain colour develops. In some butterfly species such as the Morphos, the ventral surface is mostly brown while the dorsal surface is blue. Isolating dorsal-specific cells by using apterous A as a marker can help us study how these blue scales are developing,” she elaborated.
The research team hopes to continue studying the function of the apterous A gene in butterflies. This includes determining if the gene performs similarly in other families of butterflies, including butterflies without surface-specific wing patterns, as well as investigating the way in which the gene represses eyespot pattern development.
See press release.