Since classifications have existed, wall lizards have been known to exhibit a diversity of throat colors, a phenomenon that remained stable until now. Currently, this palette is diminishing at an accelerated rate. This rapid transformation, observed over an astonishingly short period, shows how an ancient balance can unravel under the pressure of a new form.
In many animals, color differences, called morphs, are not merely aesthetic. They often correspond to distinct strategies for occupying territories or attracting mates. For example, certain shades can signal dominance, while others facilitate social interactions. This diversity allows multiple approaches to coexist within the same population.
The spread of "Hulk" lizards leads to the loss of yellow and orange colors in the landscape.
Credit: Roberto García Roa The wall lizard, a Mediterranean species, was known for three throat colors: white, yellow, and orange. This chromatic triad persisted for ages, symbolizing an evolutionary balance where each morph found its niche. Scientists saw this as a classic example of long-term biodiversity maintenance. However, recent data indicate that this stability is disappearing.
The appearance of larger, bright green, and highly aggressive lizards has disrupted this established order. Nicknamed "Hulk," these individuals monopolize resources and mating opportunities due to their dominance. Their behavior alters social interactions, leading to the decline and eventual disappearance of yellow and orange morphs. Only the white form remains alongside the green one in many areas, marking a profound upheaval in the species' dynamics.
A study published in
Science, led by researchers from Lund University, analyzed data from about 240 populations and over 10,000 individuals. The results confirm that "Hulk" lizards destabilize the social systems that allowed the coexistence of colors. The aggression of these newcomers gradually eliminates the less competitive variants, providing a striking example of how evolution—here aggression associated with the color green—can rapidly reshape an entire population.
This case shows that evolution can occur quickly and unexpectedly. The emergence of a trait, like the aggression of "Hulk" lizards, can lead to profound changes in record time.
Yellow and orange colors have disappeared over time under the influence of dominant lizards.
Credit: Roberto García Roa