Genetic isolation by distance underlies colour pattern divergence in red‐eyed treefrogs (Agalychnis callidryas)

• Published in: Molecular ecology 2022-03, Vol.31 (6), p.1666-1681
• Main Authors: Clark, Meaghan I., Bradburd, Gideon S., Akopyan, Maria, Vega, Andres, Rosenblum, Erica Bree, Robertson, Jeanne M.
• Format: Article
• Language: English
• Subjects: Agalychnis callidryas; Animals; Anura - genetics; Color; colour‐pattern polymorphism; Costa Rica; Divergence; Evolution; Frogs; Gene polymorphism; Genetic analysis; Genetic diversity; Genetic Drift; Genetic isolation; Genetic structure; Genetic Variation - genetics; Hybridization; Mutation; Nucleotides; Patterning; Phenotype; Phenotypes; Phenotypic variations; Polymorphism; Population genetics; Reproductive Isolation; Single-nucleotide polymorphism; Spatial distribution; Transition zone
• ISSN: 0962-1083; 1365-294X
• DOI: 10.1111/mec.16350

Investigating the spatial distribution of genetic and phenotypic variation can provide insights into the evolutionary processes that shape diversity in natural systems. We characterized patterns of genetic and phenotypic diversity to learn about drivers of colour‐pattern diversification in red‐eyed treefrogs (Agalychnis callidryas) in Costa Rica. Along the Pacific coast, red‐eyed treefrogs have conspicuous leg colour patterning that transitions from orange in the north to purple in the south. We measured phenotypic variation of frogs, with increased sampling at sites where the orange‐to‐purple transition occurs. At the transition zone, we discovered the co‐occurrence of multiple colour‐pattern morphs. To explore possible causes of this variation, we generated a single nucleotide polymorphism data set to analyse population genetic structure, measure genetic diversity and infer the processes that mediate genotype–phenotype dynamics. We investigated how patterns of genetic relatedness correspond to individual measures of colour pattern along the coast, including testing for the role of hybridization in geographic regions where orange and purple phenotypic groups co‐occur. We found no evidence that colour‐pattern polymorphism in the transition zone arose through recent hybridization. Instead, a strong pattern of genetic isolation by distance indicates that colour‐pattern variation was either retained through other processes such as ancestral colour polymorphisms or ancient secondary contact, or else it was generated by novel mutations. We found that phenotype changes along the Pacific coast more than would be expected based on genetic divergence and geographic distance alone. Combined, our results suggest the possibility of selective pressures acting on colour pattern at a small geographic scale. Resumen La investigación de la distribución espacial de la variación genética y fenotípica puede proporcionar información sobre los procesos evolutivos que dan forma a la diversidad en los sistemas naturales. Caracterizamos patrones de diversidad genética y fenotípica para conocer los impulsores de la diversificación de patrones de color en ranas con ojos rojos (Agalychnis callidryas) en Costa Rica. A lo largo de la costa del Pacífico, las ranas con ojos rojos tienen un patrón de color llamativo en las patas que cambia de naranja en el norte a púrpura en el sur. Medimos la variación fenotípica de las ranas en los sitios del Pacífico, con un mayor muestreo en los sitio