Aggressive wall lizard provides clues to understanding evolution

Body shape, color and behavior often evolve together as species adapt to their environment. Researchers from Lund University in Sweden have studied this phenomenon in a specific type of large, bright green and aggressive common wall lizard found near the Mediterranean. They discovered that a unique cell type might have played a key role in this joint evolution.

Adaptation is a genetic change that results in increased viability in the surrounding environment. It may affect color, shape and behavior. However, the basis for how this works genetically has remained shrouded in mystery.

In a new study, evolutionary biologists have combined field work and DNA analysis to study large, green, aggressive and sexually prominent wall lizards in the Mediterranean region. They discovered a number of genes responsible for the lizard's Hulk-like appearance. The paper is published in the journal Science Advances.

"All tissues and organs that are behind the Hulk-like appearance develop from cells called neural crest cells that form in the early embryo. We believe that the cells that underlie changes in shape, color and behavior are regulated together, and that the traits therefore evolve together," says Nathalie Feiner, evolutionary biologist at Lund University.

The research group investigated a common wall lizard with green and black coloring, impressive body size and aggressive behavior. Males with this appearance emerged many thousands of years ago, close to present-day Rome, and have shown themselves to be dominant over males with other color combinations. This has resulted in the Hulk lizards spreading throughout Italy.

"Our knowledge of neural crest cells comes almost entirely from a few model organisms, such as mice. We are now charting this type of cell in lizard embryos in order to understand how phenomena such as the Hulk lizard can evolve," says Feiner.

Over the next few years, Feiner and her team will conduct more field studies, set up breeding groups and undertake advanced genetic analyses, including using the CrispR-Cas9 gene-editing technique. All with the aim of establishing what role neural crest cells play in the intertwined evolution of color, shape and behavior.

"Our focus is on lizards, but our discoveries can probably be applied to all animals with neural crest cells, which would cover around 70,000 species of vertebrate. Although our work provides a possible explanation to how evolution works, it is also the beginning of many new areas of research," she says.