An intronic transposon insertion associates with a trans-species color polymorphism in Midas cichlid fishes

Polymorphisms have fascinated biologists for a long time, but their genetic underpinnings often remain elusive. Here, we aim to uncover the genetic basis of the gold/dark polymorphism that is eponymous of Midas cichlid fish (Amphilophus spp.) adaptive radiations in Nicaraguan crater lakes. While most Midas cichlids are of the melanic dark morph, about 10% of individuals lose their melanic pigmentation during their ontogeny and transition into a conspicuous gold morph. Using a new haplotype-resolved long-read assembly we discover an 8.2 kb, transposon-derived inverted repeat in an intron of an undescribed gene, which we term goldentouch in reference to the Greek myth of King Midas. The gene goldentouch is differentially expressed between morphs, presumably due to structural implications of inverted repeats in both DNA and/or RNA (cruciform and hairpin formation). The near-perfect association of the insertion with the phenotype across independent populations suggests that it likely underlies this trans-specific, stable polymorphism. Roughly one in ten Midas cichlid fishes loses their characteristic dark coloration and transforms into a gold morph. Here, the authors describe a transposon insertion in the gene goldentouch likely constitute the genetic basis of this polymorphism.

Automated summary

This study uncovers the genetic basis of the gold/dark polymorphism in Midas cichlid fish by identifying a transposon insertion in the gene goldentouch.