Lizard You will give muralis nigriventris it may not grow to freakish size and smash everything in sight, but evolution has turned this lizard into an Incredible Hulk of sorts — green skin included. P. nigriventris is something of a formidable Marvel superhero compared to other strains of common wall lizards (Podarcis muralis). While the common version tends to be relatively small and brownish to greenish brown, nigriventris the subspecies found in central Italy is visually striking due to its green(e) skin with black markings, larger size and increased aggressiveness.
A team of evolutionary biologists led by Nathalie Feiner from Lund University in Sweden decided to find out which genes contributed to the creation of P. nigriventris so Hulkish. Like many fictional people with superpowers (but unlike the mutant Hulk), this lizard is a hybrid.
Powerful hybrids
Although wall lizards are found from the Iberian Peninsula to Asia Minor, the researchers focused on lizards from populations in central Italy (lineage IT) and the southern Alps (lineage SA). These lineages most likely diverged from a common ancestor 5–6 million years ago and then began to hybridize—individuals from 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 were carried over 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. Traits the researchers focused on were back and belly coloration, lateral blue spots, body weight and head length.
Because P. nigriventris traits have entered the SA lineage through introgression, it can be difficult to determine what is truly ancestral. First, it was assumed that females select for P nigriventris traits in males, which increased their chances of finding a mate. However, some of these traits were later observed in females, so these traits are not exclusive to males competing for females.
“Different lines of evidence support the existence [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.
Brownish P. muralis are considered an ancestral phenotype. To see how nigriventris If a phenotype appeared, Feiner would have to find where in the lizard’s genome the characters that make up that phenotype were located.
Green genes
What Feiner and her team discovered when they analyzed the lizard genomes was that traits that P. nigriventris genes that regulate neural crest cells are identified. Formed during the early embryonic stage, these multipotent stem cells can transform into a variety of more specialized cell types throughout the embryo that contribute to everything from heart valves to coloration.
One such gene, 10 Rbm, regulates the proliferation of neural crest cells, which means their growth and division, while others, Tfcp2l1, regulates how they differentiate into more specialized cells during embryo development. yet another Gpc3, it is required for neural crest cells to migrate to various locations in the embryo where they integrate into tissues.
But where was the difference that would eventually change the coloring nigriventris phenotype? The answer was in a region of the chromosome that contains a gene known as rab18, which also helps with the migration of neural crest cells. Rab18 and Acbd5 both play a role in pigment production. This could be related to the green and black coloring P. nigriventris.
“Gene flow analyzes revealed that this is the case [chromosomal] the region likely introgressed from the IT lineage into highly expressing SA lineage populations nigriventris phenotype,” the researchers said in the same study.
While the exact factors that caused these green and black P. nigriventris monsters (at least the monsters next to them P. muralis relatives) to evolve different coloration to adapt to changes in their environment are still unknown, where their appearance comes from is no longer a mystery.
At least the Lizards with the Hulk don’t have to be exposed to extreme radiation to get their size, color and strength, unlike Bruce Banner himself.
Science Advances, 2024. DOI: 10.1126/sciadv.adk9315