KU Leuven: Yellow color makes mating more efficient in locust swarm


An international team of researchers led by Professor Jozef Vanden Broeck (KU Leuven) discovered why adult male desert locusts in a swarm have a yellow color, in contrast to their brownish female counterparts. This color difference allows the male grasshoppers to recognize the fertile females during mating in a large swarm and prevent them from ending up with another male or an already formed pair. The research results are published today in the scientific journal PNAS .

Chameleons, frogs, octopuses, arctic foxes, spiders, seahorses… they can all adapt the color of their skin or fur to the environment. That way they are perfectly camouflaged and unnoticed by other animals. Young desert locusts also come in different colors, although there is another explanation for this. When born in a small population, they disperse in the landscape and – like many other animals – develop a camouflage color that makes them inconspicuous in their environment. However, young grasshoppers that end up in a large group turn very striking yellow and black, similar to the colors of a wasp. This color pattern has previously been shown to keep natural enemies at bay.

Strikingly, young grasshoppers that grow up scattered in the landscape develop into inconspicuous brownish adult males and females. In their congeners, which occur in large groups and eventually form immense swarms, a clear distinction can be made between brownish, fertile females and bright yellow, fertile males. This observation already happened in 1921, when it was discovered that desert locusts usually occur solitary, but under favorable living conditions form huge groups. In contrast, the underlying reason for the striking yellow color of adult males living in large groups remained unknown for another 100 years.

Color change is often used by animals as a defense mechanism to hide from predators. The fact that adult males with their yellow color just stand out in a group is an unusual phenomenon. So there had to be an important reason for it.

The results show that during mating, male grasshoppers have a hard time distinguishing between female conspecifics and males in which the production of the protein responsible for the yellow color is blocked. With the yellow color as a visual signal, so that adult males avoid each other, this process turns out to be very efficient. In nature, this happens in a huge swarm that can contain about 50 million grasshoppers per square kilometer, so that the choice of a partner should be made quickly and without major conflict.

“The yellow color therefore serves as a necessary recognition feature between male conspecifics to allow mating in a large flock to go well and thus to maintain the population. This yellow color is not necessary for the scattered, solitary grasshoppers and may even be detrimental to their survival because they then lose their camouflage effect,” explains Professor Vanden Broeck.

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