Natural selection has been a mystery because it has favored structural colors like iridescence that are stunning to behold.
From dazzling hummingbirds to skinks shining in rainbow to jewel-like flies, metallic sheens have evolved many times across the animal kingdom. Sexual selection has played a role in some animals where the iridescence is more prominent in one sex than the other.
The groundsel bush beetles are only iridescent in their larval forms, but both sexes are equally iridescent in many insects. Experiments show that the color shifts may serve a protective function in these animals.
One of the challenges when studying the functions of highly reflective structural coloration has been to separate the effects of changeability of colors, the hallmark of iridescence, from the effects of simply having multiple colors at the same time.
To achieve this, Kjernsmo and colleagues set up an experiment where they tested young chickens with different types of wing cases, in the form of real and artificial jewel beetles, with a tasty mealworm snack inside.
The chicks were presented with wing cases that were either glossy with a static gradient, or matt with shifting colors.
The birds attacked the prey that displayed multiple colors at the same time. They thought twice about going for the prey. The strength of the hesitation was not as strong as the color shifted. They had no experience with iridescence.
Our new @Camo_Lab #colsci paper showing that #jewelbeetle #iridescence 🪲🌈and #gloss can protect prey by reducing the attack-willingness of naïve #birds is out now & published #openaccess in @AnimBehSociety @asab_tweets : https://t.co/qrX1rszRAm @VisionInstitute @BristolBioSci pic.twitter.com/gyTIt4CW60
— Karin Kjernsmo (@KarinKjernsmo) May 3, 2022
For the first time, we were able to test for each of these effects on their own, and found that both iridescence and gloss can protect prey even after detection.
In 2020, the same team provided evidence that iridescence may be an effective form of camouflage, even though it might seem counterintuitive given how attractive some of the brilliant structural colors can be.
This idea has never been shown before. I think it has been neglected or forgotten, according to Kjernsmo.
These results need to be demonstrated in natural conditions to confirm and ensure there is nothing else that is different from the results in the laboratory setting.
Our results are important because they show that even when prey are presented up close and against a mismatching background, iridescence may confer a survival benefit by inducing hesitation or even an aversion response in attacking birds.
They theorize that this is due to a form of aposematism, when animals use colors to advertise their poisonous nature. The poisonous warning idea was supported by a study on an iridescent Alpine leaf beetle.
The researchers of the study suggest that future studies could establish the Frequency with which the combination of iridescence and secondary defenses occurs.
Their research was published.
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