Hulk lizard” knocks out ancient color palette

As the "Hulk" lizards spread across the landscape, the yellow and orange throat colors also disappear.
 Photo Credit: Roberto García Roa

Scientific Frontline: "At a Glance" Summary

• Main Discovery: A sexually dominant, aggressive "Hulk" morph of the common wall lizard is rapidly extinguishing ancient yellow and orange throat color variants that previously coexisted for millions of years.
• Methodology: Researchers analyzed throat color distributions in over 10,000 Podarcis muralis individuals across roughly 240 populations in the Mediterranean region.
• Key Data: The dataset covers >10,000 lizards; the spread of the green "Hulk" morph correlates with the complete loss of yellow and orange phenotypes, often leaving only the white morph remaining.
• Significance: This study demonstrates that ancient, stable evolutionary polymorphisms can be collapsed abruptly by a single new trait, overturning assumptions about the inherent stability and slow pace of evolutionary balance.
• Future Application: These findings provide a model for predicting how emerging traits or invasive phenotypes can rapidly alter competitive dynamics and reduce intraspecific biodiversity.
• Branch of Science: Evolutionary Biology
• Additional Detail: The elimination of color variants is attributed specifically to the aggressive behavior of the "Hulk" morph, which destroys the social equilibrium required for multiple morphs to persist.

The "Hulk" lizard.
Photo Credit: Roberto García Roa

A myriad of colors that survived millions of years of evolution have disappeared in a short period of time. The culprit? A bright green, aggressive, and sexually dominant wall lizard that has wiped out several color variants within its species. 

Many animal species display clearly defined color variants, or color morphs. These are not just superficial differences but are often linked to different strategies for securing access to territories, mates, or similar advantages. 

The common wall lizard (Podarcis muralis) is a species widespread in the Mediterranean region, and can have three different throat colors: white, yellow, and orange. These have coexisted within the same populations for millions of years and served as a textbook example of stable evolutionary balance. However, in a new study published in Science, a research team led by Lund University shows that this balance has now been broken. 

“We are seeing how the coexistence of several different color morphs, something that has been stable for millions of years, is being lost over a very short evolutionary time scale,” says Tobias Uller, professor of evolutionary biology at Lund University. 

The yellow and orange colours disappeared over time.
Photo Credit: Roberto García Roa

Data from over 10,000 lizards 

The researchers analyzed color data from about 240 populations of wall lizards, totaling more than 10,000 individuals. The results speak for themselves. The so‑called Hulk lizards - large, aggressive lizards with a characteristic appearance - have shifted the balance within the species. 

As the "Hulk" lizards spread across the landscape, the yellow and orange throat colors also disappear. Only the white color remains. 

“The aggressive behavior disrupts the finely tuned social systems that previously enabled several color strategies to coexist,” says Tobias Uller. 

Evolution not always slow 

The color study is unique. It shows how long‑lasting sets of colors within a species can be surprisingly vulnerable. Evolution is not always slow and balanced - sometimes a single new, powerful player is enough to rewrite the rules.  

“By showing how color variants that have coexisted for millions of years are wiped out; we now better understand how the emergence of new traits changes competition in nature,” concludes Tobias Uller. 

Reference material: Wall lizard (Podarcis muralis)

Published in journal: Science

Title: Adaptive spread of a sexually selected syndrome eliminates an ancient color polymorphism in wall lizards

Authors: Tobias Uller, Nathalie Feiner, Roberto Sacchi, Marco Zuffi, Stefano Scali, Panayiotis Pafilis, Konstantinos Plavos, Javier Abalos, Pedro Andrade, Prem Aguilar, Daniele Salvi, and Geoffrey M. While

Source/Credit: Lund University | Johan Joelsson

Reference Number: ebio012126_01

Privacy Policy | Terms of Service | Contact Us