Climatic and genetic factors shape geographic color variation in the Guinan toad-headed lizard (Phrynocephalus guinanensis)

Coloration constitutes one of the most striking features of phenotypic diversity in animals, yet the evolutionary mechanisms underlying its diversification remain incompletely resolved, particularly in species expressing multiple distinct color traits. The Guinan toad-headed lizard (Phrynocephalus guinanensis), endemic to the Mugetan Desert region, exhibits pronounced ventral color polymorphism, including black, red (restricted to males), and green (restricted to females), offering a robust system to investigate the ecological and genetic drivers of coloration divergence. To identify the ecological and genetic factors governing this variation, ventral coloration was quantified in 137 individuals across 15 populations using standardized spectrophotometry and calibrated digital imaging. Generalized linear models incorporating bioclimatic data and population genetic structure showed that black pigmentation was strongly associated with mean annual temperature, consistent with a role in thermoregulation. In contrast, red and green coloration varied with population genetic structure in both sexes, suggesting divergence shaped by sexual selection. These results indicate that both climatic and genetic factors have together shaped the geographic color variation in this species, providing deeper insight into the evolutionary dynamics and diversity of animal coloration.