Convergent evolution of parrot plumage coloration

Parrots have remarkable plumage coloration that result in part from a unique ability to produce pigments called psittacofulvins that yield yellow to red feather colors. Little is known about the evolution of psittacofulvin-based pigmentation. Widespread color mutations of captive-bred parrots provide perfect opportunities to study the genetic basis of this trait. An earlier study on blue budgerigars, which do not possess psittacofulvins, reveals the involvement of an uncharacterized polyketide synthase (MuPKS) in yellow psittacofulvin synthesis. The blue phenotype had repeatedly appeared in different parrot species, similar to independent experimental replications allowing the study of convergent evolution and molecular mechanism of psittacofulvin-based pigmentation. Here, we investigated the genetic basis of the blue phenotypes in two species of Agapornis parrots, Fischer's lovebird (A. fischeri) and Yellow-collared lovebird (A. personatus). Using whole-genome data, we identified a single genomic region with size <2 Mb to be strongly associated with the color difference between blue and wild-type (WT) birds in both species. Surprisingly, we discovered that the mutation associated with the blue Agapornis phenotype was identical to the previously described substitution causing the functional change of MuPKS in budgerigars. Together with the evidence of shared blue-associated haplotypes and signatures of a selective sweep in this genomic region in both species, we demonstrated both de novo mutation and interspecific introgression play a role in the evolution of this trait in different Agapornis species. The convergent substitution in the same gene in both lovebirds and budgerigars also indicates a strong evolutionary constraint on psittacofulvin-based coloration.