The lizard Podarcis muralis nigriventris may not grow to a freakish size and destroy everything in sight, but evolution has turned this lizard into a kind of Incredible Hulk, green skin included. P. nigriventris is something like the imposing Marvel superhero compared to other species of common wall lizards (Podarcis muralis). Although the common version is relatively small and brownish to greenish brown, the nigriventris subspecies, found in central Italy, is visually impressive due to its green(er) skin with black markings, larger size and increased aggression.
A team of evolutionary biologists led by Nathalie Feiner of Lund University in Sweden decided to find out which genes helped create P. nigriventris so Hulk-like. Like many fictional people with superpowers (but unlike the mutated Hulk), this lizard is a hybrid.
Giant hybrids
Although common wall lizards are found from the Iberian Peninsula to Asia Minor, the researchers focused on lizards from populations in central Italy (IT lineage) and the southern Alps (SA lineage). These lineages most likely diverged from a common ancestor five to six million years ago and then began to hybridize: individuals from the different lineages mated with each other to produce hybrid offspring.
P. nigriventris originated as a subspecies of the IT lineage. However, some of its features have been passed down from the SA line. This is called introgression, which occurs when genetic information is transferred from one lineage or species to another as a result of hybridization. The characteristics the researchers focused on were coloration on the back and abdomen, lateral blue spots, body mass and head length.
Because P. nigriventris Because traits came into the SA lineage through introgression, it can be difficult to say what is truly ancestral. It was first assumed that women were selected P nigriventris characteristics in men, which increased their chances of finding a partner. However, some of these characteristics were later seen in women, so these characteristics are not exclusive to men competing for women.
“Several lines of evidence support the existence of [these traits] in both sexes, and [the traits] remain intact during introgression into a distantly related lineage,” the researchers said in a study recently published in Science Advances.
The brownish one P. muralis are considered the ancestral phenotype. To see how the nigriventris phenotype arose, Feiner would have to figure out where the traits that make up this phenotype were located in the lizard’s genome.
Green genes
What Feiner and her team discovered while analyzing the lizards’ genomes were the traits that make… P. nigriventris conspicuousness are determined by genes that regulate neural crest cells. These multipotent stem cells, which form during an early embryonic stage, can transform into different types of more specialized cells throughout the embryo, contributing to everything from heart valves to coloration.
One such gene, Rbm10, regulates the proliferation of neural crest cells, meaning their growth and division, while another, Tfcp2l1, regulates how they differentiate into more specialized cells as the embryo develops. Yet another, Gpc3, is necessary for neural crest cells to migrate to different sites in the embryo where they integrate into tissues.
But where was the difference that would ultimately change the color? nigriventris phenotype? The answer lay in a region of a chromosome that contains a gene, known as Rab18, which also helps in the migration of neural crest cells. Rab18 And Acbd5 both play a role in pigment production. This may have to do with the green and black color of the car P. nigriventris.
“Analyses of gene flow have shown this [chromosomal] region probably invaded from the IT lineage into populations of the SA lineage that the nigriventris phenotype,” the researchers said in the same study.
While the exact factors that caused these green and black P. nigriventris monsters (at least monsters next to them P. muralis relatives) to develop different colorations to adapt to changes in their environment are still unknown, where their appearance comes from is no longer a mystery.
At least Hulk-like lizards don’t have to expose themselves to extreme radiation to gain their size, color and strength, unlike Bruce Banner himself.
Scientific Progress, 2024. DOI: 10.1126/sciadv.adk9315