Colorful evolution: Unrivaled beauty among chameleons

When looking for a partner, animals often find themselves in a dilemma: On the one hand, they have to send out the most conspicuous signals possible in order to draw the attention of potential partners.

On the other hand, it is advisable to keep a low profile so as not to attract predators as well.

Freed from this danger in a new environment, they should quickly thrive.

Researchers led by Martin Whiting from Macquarie University in Sydney and Brenden Holland from Hawaii Pacific University in Honolulu have observed that evolution can actually take place in this way.

The biologists used the three-horned chameleon

as a research object .

Native to mountain forests in East Africa, this stately chameleon is also popular as an inhabitant of terrariums.

This location was also intended for the specimens from Kenya that arrived in Hawaii on the island of Oahu in 1972.

After the long journey, however, the animals made such a miserable impression that they should first recover outdoors.

They promptly took the opportunity to flee.

Eat or be eaten?

Unlike in their old homeland, the escapees rarely encountered birds of prey or snakes in their new environment, which regard chameleons as welcome prey.

No wonder the animals have multiplied rapidly in the mountain forests of Oahu.

Far from picky when it comes to finding nutritious bites, the newcomers are now seen as a threat to the biodiversity of native insects and snails.

Especially since three-horned chameleons like to eat prey with a shell.

, which live exclusively on Oahu,

are eaten with their packaging, as are caterpillars of native moths of the genus

, known for the enormous variety of colors and shapes of their shells.

The fact that three-horned chameleons have been so incredibly successful in colonizing the Hawaiian island of Oahu gives evolutionary biologists a chance to analyze this unplanned experiment in more detail.

Whiting and colleagues wanted to find out whether three-horned chameleons from Hawaii already behave differently in certain life situations than conspecifics in Kenya.

They focused on the color change.

After all, it is typical for chameleons to quickly adapt to different situations in this way.

Mating success through guanine crystals

When male three-horned chameleons are intimidating a rival or courting a mate, they turn bright yellow and light green.

As Whiting and his colleagues report in the "Science Advances", three-horned chameleons from Hawaii can afford particularly bright colors.

Compared to males from the presumed origin population in Kenya, the Hawaiians present themselves with a significantly higher luminance.

Accordingly, they stand out more strongly from their plant environment.

Behind this bold color are guanine crystals that reflect light: when they are distributed over large areas in special skin cells, the pigments of the color cells above them appear brighter.

With skin cells in which the black-brown pigment melanin spreads, the chameleons can darken their appearance.

Not only do the mostly polled females make use of this, a male that is defeated in a duel also quickly changes to inconspicuous colors.

While a male three-horned chameleon adorns itself with bright colors, it not only catches the eye of its conspecifics.

It also risks attracting the attention of animals hungry for prey.

The evolution should lead to a compromise between imposing colors and sufficient camouflage.

To test how colorful male chameleons react to animals that target them in Kenya, they were confronted with a stuffed hawk and a lifelike model of a tree snake.

It turned out that Kenyan three-horned chameleons make themselves much more inconspicuous when they see a suspected threat.

Their Hawaiian counterparts dim their colorful outfit far less.

They can afford that too.

Because in Hawaii, domestic cats and feral cats are the greatest danger, i.e. animals for which color does not play a major role.

Adorning themselves with bright colors for social interactions therefore does not pose any particular risk for male three-horned chameleons there.

However, it probably improves the chances of success with the opposite sex.

Half a century was enough to change the behavior of the chameleons accordingly: Evolution has given males who are looking for mating attractive, brightly colored Hawaiian shirts, so to speak.

However, only for the time when the male three-horned chameleons are trying to find a partner and have to compete with rivals.

For most of their lives, they also play it safe in Hawaii and, like the females, dress in camouflage colors.