Butterflies Mimic Wing Coloration Of Toxic Counterparts To Ward Off Birds

Mimicry is a valuable trait for some butterflies hoping to avoid predation. That is, some butterflies have the ability to become poisonous and unappetizing by ingesting chemical defenses from the plants they feed on as caterpillars. Knowing this, some fairly harmless butterflies simply mimic others' warning-signal colorations and wing patterns, which are also called "aposematic" and make it look as if they too are poisonous. In order to better understand this defense mechanism, researchers from the National Centre for Biological Sciences (NCBS) and the National University of Singapore (NUS) investigated how well butterflies are actually able to resemble their lethal counterparts. 

For their study, researchers examined mimetic butterfly communities called "butterfly rings" from the Western Ghats of India. Butterflies are considered a delicacy for insectivorous birds, so researchers were interested in how similar mimicking butterflies appeared to bird predators, compared to their aposematic friends, according to a news release. 

It turns out that female butterflies are actually better at mimicry than males, researchers revealed in their study. This is attributed to the fact that males have to sport brighter colored wings in order to attract females for breeding, the release noted. 

"Female butterflies carry heavy loads of eggs, which impairs their escape flight when they are attacked by birds and other predators. Because of this risk of predation, female butterflies are under intense natural selection to be very good mimics. Therefore, it makes sense that females are better mimics than males," Krushnamegh Kunte, one of the researchers from NCBS, explained in the release. 

That said, the opposing forces of natural selection on females and sexual selection on males can ultimately lead to less reproductive success in the long run and cause males and females of the same species to look radically different. This is known as sexually dimorphic and generally occurs when females are mimicked but males are not. 

Oftentimes, when males and females lacking the genetics for mimicry mate, the chance that their offspring will be able to do so is also low. In this case, one would expect females to be very poor mimics. However, researchers were rather surprised by the fact that female-limited butterflies were still able to resemble their aposematic counterparts. This suggests that natural selection is strong enough to overcome the effects of genetics, the researchers explained. 

Researchers also explored the theory that certain wings of a butterfly may be able to mimic warming colorations more successfully than others. This would be possible because only the upper wing surfaces are exposed during flight and visible to bird predators. Therefore the upper wings would need to be able to mimic the colors of other butterflies, while the ventral, or underside, wing surfaces could remain unchanged, researchers noted. 

However, researchers discovered the exact opposite happens. In actuality, the lower sides of butterfly wings are better mimics than the upper sides. Researchers explained that this may because the butterflies have adapted to bird predation while they are at rest, during which time their wings are folded and the undersides are visible. However, further researcher is required to better explain the evolutionary abilities of mimicry. 

"Although the first result was easy to understand, the other two results were surprisingly counter to expectations. This paper throws open new questions about the evolution of mimicry and the selective forces that influence the evolution of butterfly wing patterns. Many of these questions are amenable to experimental analysis and we hope to have some more answers soon," Kunte added in the release. 

Their findings were recently published in the journal Evolution.

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