‘Who’d guess they’re the same species?’ What Italy’s wall lizards reveal about genetic diversity and why it matters | Biodiversity
TTwelve kilometers from the heart of Rome, Dr. Javier Ábalos stops his walk, raises his sunglasses and points. To his right, perched on a rock wall, sits a magnificent lizard. Its body is covered in charcoal black tones speckled with bright yellow on a green back, and its head, with a prominent jaw, is dotted with fluorescent blue spots. The reptile basks in the sun, indifferent to our presence.
After about 130 kilometers of driving on the road that connects the capital to the small village of Poggio di Roio, the researcher from the University of Valencia has barely gotten out of the car when he sees another lizard. This one is smaller, with a brownish body and a narrower head furrowed by a network of dark stripes.
Even after more than a decade of studying color variations among European lizards, their differences still amaze Ábalos. “Who would guess they are the same species?” » he said smiling.
Despite their obvious differences, both animals are adult males of the wall lizard (Podarcis muralis), a widespread species whose remarkable variation in color, size and behavior reveals a crucial dimension of biodiversity: variation within species.
Lizards are proof that biodiversity is much more complex than a simple inventory of species inhabiting an ecosystem.
Differences in rostral ornaments, or horns, among male Parson’s chameleons (Calumma parsonii) in Madagascar, the social or dietary behaviors of chimpanzee populations (Pan troglodytes), regional song dialects in white-crowned sparrows (Zonotrichia leucophrys), or the color variation in common wall lizards are all expressions of biodiversity within species. And this biodiversity is not static, but often evolves at the rate of evolution.
When it comes to the wall lizard, three alternative body colorations (called white, yellow and orange “morphs”) have coexisted for millions of years in Italy in what researchers describe as a delicate and enigmatic balance maintained by complex social and sexual interactions.
Some males have a brown body with a pale, almost white throat and belly. Others have yellow undersides, while a third group has bright orange or reddish colors.
However, these three forms are no longer the only ones. A study recently published in Science suggests that the emergence of a fourth variation of the species (a larger form with a bright green dorsal color over black reticulation, known as nigriventris) could disrupt the ancient balance and potentially drive the three original forms toward extinction.
The study, carried out by an international team of researchers, measured the coloration of 2,506 lizards captured in 148 sites in Italy and reconstructed the evolutionary history of the populations studied.
Their results show that the spread of this new, larger, darker and more aggressive nigriventris form (which may have originated from ancient islands that existed in the Rome Basin during the Pliocene and Pleistocene eras) could distort competition between males, leaving the white, yellow and orange forms struggling to persist.
“We see how the coexistence of different color forms – something that has been stable for millions of years – is lost on a very short evolutionary time scale,” explains Professor Tobias Uller, from Lund University in Sweden, who led the study.
“By showing how color variants that have coexisted for millions of years can be eliminated, we now better understand how the emergence of new traits alters the natural processes that maintain diversity within species. »
In nature, biodiversity within species extends beyond appearance. Genetic, behavioral, and morphological variations shape not only what a species is, but also what it might become, providing a reservoir of traits that can help populations cope with present and future challenges to survival and reproduction.
Dr Nathalie Feiner, from the Max Planck Institute and co-author of the study, says: “Without such variation, evolution would stop and the ability to adapt would be lost.
“Understanding and preventing the erosion of this diversity is therefore at the very heart of conservation biology. »
However, nature does not develop in isolation. Human pressures can also push biodiversity (including within species) towards collapse. Here again, wall lizards provide insight.
A group of researchers, some of whom contributed to the wall lizard study, are working hard to save one of Europe’s most endangered vertebrates: the aeolian wall lizard (Podarcis raffonei). Their goal is to prevent extinction, but also to preserve the diversity that defines the species.
For millions of years, Aeolian wall lizards have inhabited a few small islets in the Aeolian archipelago, north of Sicily. On each islet, the lizards display distinctive colors, ranging from pale brown to emerald green. Today, habitat degradation, the presence of the invasive black rat and, above all, the introduction of the Italian wall lizard (Podarcis siculus), threaten their survival.
Research shows that Aeolian wall lizards behave poorly during encounters with invasive lizards, as they compete for food and shelter, being attacked and having to escape more frequently. The strong competitive advantage of invaders often results in territorial monopolization, reducing the breeding possibilities of Aeolian wall lizards.
In response, researchers launched the Life Eolizard Conservation Project in 2023. The initiative combines habitat restoration (such as vegetation recovery), rat control, and removal of invasive lizards.
The scientists also launched captive breeding programs for two populations of aeolian lizards with different morphological and genetic backgrounds at the Bioparco Zoological Center in Rome.
“In 2025, we selected breeding pairs using genomic data and produced the first 64 juveniles of this species born in captivity,” explains Dr Daniele Salvi, from the University of L’Aquila, one of the main researchers of the project.
“This allows us to maximize genetic diversity and resilience so that reintroductions hit the ground running in the wild.”
The ultimate goal is to reintroduce these captive-bred individuals into restored island ecosystems in the near future.
Dr Leonardo Vignoli from Roma Tre University, coordinator of Eolizard, says: “The creation of a dedicated sanctuary on two small islets – Lisca Bianca and Bottaro – is a turning point for the species.
“We are creating safe strongholds where the aeolian wall lizard can thrive again. This doesn’t just increase numbers, it reshapes the distribution of the species, expanding it into areas that have been lost and significantly improving its chances of long-term survival.”
Diversity within species contributes to the functioning of ecosystems and represents an often overlooked layer of biodiversity.
Uller says: “Understanding why wall lizards have this extraordinary ability to generate diversity is fascinating and brings us closer to understanding why nature works the way it does. »
