Ancient Lizard Colour Morphs Threatened by Aggressive Newcomer in Italy
Just twelve miles from the bustling heart of Rome, Dr Javier Ábalos, a researcher from the University of Valencia, pauses during a walk and points to a rocky wall. There, basking in the sun, sits a strikingly beautiful lizard. Its body is coated in charcoal-black tones speckled with vibrant yellow across a green dorsum, and its head features a prominent jaw splashed with fluorescent blue spots. The reptile appears utterly unconcerned by human presence.
Approximately eighty miles farther along the road connecting Rome to the small village of Poggio di Roio, Ábalos has barely stepped out of his car when he spots another lizard. This one is smaller, with a brownish body and a narrower head crisscrossed by a network of dark stripes. Despite their obvious differences, both animals are adult males of the common wall lizard, scientifically known as Podarcis muralis. This widespread species exhibits remarkable variation in colour, size, and behaviour, revealing a crucial dimension of biodiversity: the variation within species.
The Delicate Balance of Colour Morphs
For millions of years, three alternative body colourations, known as white, yellow, and orange morphs, have coexisted in Italy. Researchers describe this coexistence as a delicate and enigmatic balance maintained through complex social and sexual interactions. Some males display brown bodies with pale, almost white, throats and bellies. Others show yellow undersides, while a third group exhibits bright orange or reddish colours.
However, these three morphs are no longer the only ones. A recently published study in the journal Science suggests that the emergence of a fourth variation, known as nigriventris, could disrupt this ancient equilibrium. The nigriventris morph is bulkier, with a bright green dorsal colour over a pitch-black reticulation, and it is notably more aggressive than its relatives.
Research Findings and Evolutionary Threats
The study, led by an international team of researchers including Prof Tobias Uller of Lund University in Sweden, involved measuring the colouration of 2,506 lizards captured across 148 locations in Italy. The team reconstructed the evolutionary history of these populations. Their results indicate that the spread of the nigriventris form, which may have originated on ancient islands in the Rome basin during the Pliocene and Pleistocene epochs, could skew competition among males.
This new morph's larger size and aggressive behaviour leave the white, yellow, and orange morphs struggling to persist. Prof Uller explains, "We are seeing how the coexistence of different colour morphs – something that has been stable for millions of years – is being lost over a very short evolutionary timescale." He adds that by showing how colour variants that have coexisted for millennia can be wiped out, researchers now better understand how the emergence of new traits changes the natural processes that maintain diversity within species.
The Broader Implications of Intraspecific Biodiversity
In nature, biodiversity within species extends far beyond mere appearance. Genetic, behavioural, and morphological variation shape not only what a species is but also what it might become. This variation offers a reservoir of traits that may help populations face present and future challenges to survival and reproduction. Dr Nathalie Feiner of the Max Planck Institute, a co-author of the study, emphasises, "Without such variation, evolution would stall, and the capacity for adaptation would be lost. Understanding and preventing the erosion of this diversity therefore lies at the very core of conservation biology."
Human pressures can also push biodiversity, including within species, towards collapse. The common wall lizard study provides insight into this, as similar threats are affecting other species. For instance, the Aeolian wall lizard (Podarcis raffonei), one of Europe's most endangered vertebrates, is facing extinction due to habitat degradation, invasive black rats, and the introduction of the Italian wall lizard (Podarcis siculus).
Conservation Efforts for the Aeolian Wall Lizard
Researchers have launched the Life Eolizard conservation project in 2023 to save the Aeolian wall lizard. This initiative combines habitat restoration, such as vegetation recovery, rat control, and the removal of invasive lizards. Scientists have also begun captive breeding programmes at Rome's Bioparco zoological centre, focusing on two Aeolian lizard populations with different morphological and genetic backgrounds.
Dr Daniele Salvi of the University of L'Aquila, one of the project's lead researchers, states, "In 2025, we selected breeding pairs using genomic data and produced the first 64 captive-born juveniles of this species. This allows us to maximise genetic diversity and resilience so reintroductions start off strong in the wild." The ultimate aim is to reintroduce these captive-bred individuals into restored island ecosystems in the near future.
Dr Leonardo Vignoli of Roma Tre University, coordinator of Eolizard, highlights the creation of dedicated sanctuaries on two small islets, Lisca Bianca and Bottaro. He says, "We are creating safe strongholds where the Aeolian wall lizard can thrive again. This doesn't just boost numbers, it reshapes the species' distribution, expanding it into areas that were lost and dramatically improving its chances of long-term survival."
Conclusion: The Importance of Intraspecific Diversity
Diversity within species contributes significantly to ecosystem functioning and represents an often-overlooked layer of biodiversity. Prof Uller reflects, "Understanding why wall lizards have this extraordinary capacity to generate diversity is fascinating and brings us closer to understanding why nature works the way it does." The threat to the common wall lizard's colour morphs serves as a stark reminder of the fragility of intraspecific biodiversity and the urgent need for conservation efforts to preserve these unique variations for future generations.
