Study reveals how aggressive 'Hulk' lizards are wiping out millions of years of evolution

Humans for ages believed that wall lizards coexisted in three distinct color types, each with its own strategy for survival. 

For millions of years, scientists observed a vibrant mix of colors persisted within a single lizard species, but now, much of that diversity has vanished in a remarkably short time.

Strangely, researchers pointed to an unexpected cause: a bold green, highly aggressive, and dominant wall lizard that has rapidly eliminated several color forms within its own species.

Now, a powerful green variant is taking over. These dominant “Hulk” lizards are outcompeting the others, causing yellow and orange morphs to vanish. 

It’s a dramatic reminder that evolution can flip the script much faster than expected.

In many animal species, distinct color types, known as color morphs, are more than just visual differences. 

These variations often reflect different approaches to survival, such as how individuals compete for territory or attract mates. 

Each color can represent a unique strategy that helps maintain balance within a population.

The common wall lizard, or Podarcis Muralis, found widely across the Mediterranean, has long been a classic example of this balance.

As per researchers, these individuals typically display one of three throat colors: white, yellow, or orange. 

For millions of years, these color morphs coexisted within the same populations, maintaining a stable evolutionary system.

Analyzing more than 10,000 individual lizards. The findings were clear. A group informally known as "Hulk" lizards has altered the dynamics within the species.

To understand what is happening, researchers examined color patterns across about 240 populations.

These larger, more aggressive lizards, recognized by their striking appearance, have spread rapidly. As they expand into new areas, the yellow and orange throat variants are disappearing. In many places, only the white morph remains.

"The aggressive behavior disrupts the finely tuned social systems that previously enabled several color strategies to coexist," said researcher Tobias Uller, a professor of evolutionary biology at Lund University.

This research highlights how even long-standing evolutionary systems can be fragile and a single dominant trait can reshape competition and alter the balance within a species in a short time.

The research led by Lund University was originally published in the journal Adaptive spread of a sexually selected syndrome eliminates an ancient color polymorphism in wall lizards.