This Diminutive Reptile Plays Its Own Version of Rock‑Paper‑Scissors

What the Game Looks Like in the Wild

Among the sun‑baked rocks of the western United States, the Uta stansburiana—commonly known as the side‑blotched lizard—engages in a surprisingly strategic battle for territory and mates. Researchers have long observed three distinct male colour morphs, each with a different throat patch: orange, blue, and yellow. These morphs do not merely differ in hue; they embody a cyclical dominance system that mirrors the classic hand game rock‑paper‑scissors.

How the “Rock‑Paper‑Scissors” Cycle Works

Orange‑throated males are the most aggressive. They defend large territories and can easily overpower blue‑throated rivals, who are better at sneaking into an opponent’s nest. However, yellow‑throated males excel at mimicking the female’s coloration, allowing them to slip past the vigilant orange males and steal their mates. In turn, the blue males can outmaneuver the deceptive yellows by guarding their mates more effectively.

The result is a never‑ending loop: orange beats blue, blue beats yellow, and yellow beats orange. No single strategy can dominate forever, keeping the population in a dynamic equilibrium.

The New Study that Unveiled the Mechanism

In a paper published this month in Nature Ecology & Evolution, a team led by Dr. Samantha Reyes of the University of Arizona combined field observations with genetic analysis to decode the underlying biology of this tri‑morphic system. The researchers:

• Tracked over 1,200 individual lizards across three desert sites for two breeding seasons.
• Sequenced the genomes of each colour morph to identify alleles linked to hormone production and behavior.
• Conducted controlled laboratory experiments to test how altering hormone levels changed a male’s aggression and mating tactics.

The findings reveal that a single supergene—a tightly linked cluster of genes—governs both the throat coloration and the associated behavioral repertoire. This supergene is inherited in a Mendelian fashion, ensuring that each male receives one of the three possible morphs.

Why This Matters

The study provides a rare glimpse into how complex social interactions can be encoded genetically. It also demonstrates that “rock‑paper‑scissors” dynamics are not just a metaphor but a real evolutionary strategy that can maintain genetic diversity within a species. Understanding such mechanisms could help conservationists predict how populations might respond to environmental changes that disrupt the balance of these interactions.

Future Directions

Dr. Reyes and her colleagues plan to explore whether similar supergene‑driven cycles exist in other reptiles and amphibians. They are also investigating how climate‑driven shifts in habitat might tilt the balance toward one morph, potentially threatening the long‑term stability of the system.

By Emily Carter, Science Correspondent