AsianScientist (Aug. 27, 2021) – Too much of anything can be a bad thing—for bush brown butterflies, having more eyespots on their forewings is akin to flashing neon signs to trigger predatory attacks. Researchers from the National University of Singapore (NUS) published their findings in the Proceedings of the Royal Society B.
Thought to help defend against predation, butterflies’ wings are nothing short of dazzling, with many species showcasing rings called eyespots. With their stand-out colors, however, these circular markings are in fact easily spotted by predators.
But their protective function lies in their strategic positions on the wings. Often, eyespots are found along the wing margins or on the hindwings, which are considered less important parts of the body. When predators attack these parts, butterflies can often escape from their attackers’ clutches with little significant damage.
While the bush brown butterfly, Bicyclus anynana, typically has half as many forewing eyespots than the hindwings, NUS scientists investigated whether variations in this number affected predation. Butterflies that bared more forewing eyespots suffered from more intense attacks, leading to a sharp drop in their population.
After unleashing mantid insects in a series of experiments, the team compared the extent of damage sustained by butterflies with either two or four eyespots on their forewings. Both groups had injured hindwings, but those with the extra eyespots had become easy targets of predation, with their forewings also experiencing a battering.
As forewings are especially critical for agile maneuvers to evade predators, attacking this part turned out to be particularly disastrous to the butterflies’ flight. According to the researchers, butterflies are usually able to cope with damaged hindwings, but broken forewings make them more vulnerable to future attacks—quite literally dealing a death blow to their survivability.
With shorter lifespans, these four-eyespot butterflies also had less time to lay eggs, the team found. These results might just hold the story behind why bush brown butterflies evolved to have fewer forewing eyespots. Those having more eyespots likely meet their demise too soon before they can produce offspring to bear the same pattern.
More than being a sight for sore eyes, eyespot number diversity remains an interesting phenomenon to study, especially as other butterfly species have the opposite pattern, carrying more forewing eyespots than hindwing. For the researchers, exploring entire communities of predator-prey relations will be key to understanding how and why these wing patterns came to be.
“Our findings demonstrate how the location of eyespots on butterfly wings both influences and is influenced by the behavior of their predators, revealing more of the complexity behind how animals communicate to one another,” said corresponding author Professor Antonia Monteiro from NUS.
The article can be found at: Chan et al. (2021) Predation Favors Bicyclus anynana Butterflies with Fewer Forewing Eyespots.
Source: National University of Singapore; Photo: David Clode/Unsplash.
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