Instability of chromatophore maintenance as a potential route to transgressive color diversification: evidence from a hybrid grouper.

Groupers play an important role in coral reef ecosystems as top predators, but much remains unknown about their diverse colorations. Hulong hybrid grouper (Epinephelus fuscoguttatus ♀×E. lanceolatus ♂) typically exhibits a black-brown patterned appearance but occasionally aberrant morphs, including pure white, pure yellow, and variegated forms which exceed the phenotypic range of either parent. What is the physiological basis of these transgressive colorations? Does each aberrant phenotype reflect an independent underlying state? Here, we combined long-term phenotypic observation with cytological analyses, transcriptome profiling and metabolomic assays of skin tissues from Hulong hybrid grouper. Cytological analyses revealed severe alterations in chromatophore composition. Color transitions documented in a single individual, together with multi-omics analyses, suggested that phenotypically diverse individuals possess an intrinsically unified and labile pigmentation system. These findings provide new insights into how coloration diversity is generated in hybrid offspring, and present Hulong hybrid grouper as an emerging model system for studying the evolution of novel color traits in fishes.