Pigments, Chromatophore Structure, and Gene Expression Underlying Colour Polytypy of a Panamanian Poison Frog

Colour polytypism represents an example of phenotypic diversification shaped by genetic divergence and ecological pressures. Poison frogs of the genus Oophaga (Dendrobatidae) are highly polytypic in coloration, making them an ideal system for investigating the genetic and physiological basis of colour variation. We examined gene expression, pigment and histological differences across four colour morphs (aquamarine, brown, green, and red) of Oophaga vicentei from mainland Panama. RNA sequencing revealed 1838 and 5085 differentially expressed genes (DEGs) in the skin and liver, respectively. Melanin synthesis genes were upregulated in the brown morph, whereas pteridine pathway genes were upregulated in red and green morphs, consistent with previous findings in O. pumilio. In aquamarine frogs, pigment composition was similar to brown and green frogs, but transcriptional profiles were highly divergent. Red morphs upregulate a paralog of the dendrobatid ketolase cyp3a80 in the liver, suggesting modified ketolation mechanisms in O. vicentei. This is consistent with higher ketocarotenoid accumulation in red frogs. Co-expression network analysis identified morph-related modules in both tissues but the relationship between modules and known pigmentation pathways remains unclear. Comparative analysis across seven dendrobatid species revealed conserved pigmentation genes (e.g., xdh, ttc3b) alongside morph-specific expression patterns. Our results show that red frogs are dissimilar in pigments, chromatophore structure, and gene expression, whereas aquamarine, brown, and green coloration share overlapping pigment profiles and chromatophore organisation, with transcriptional differences suggesting structural or regulatory mechanisms.