The meaning of melanin, carotenoid, and pterin pigments in the bluefin killifish, Lucania goodei

Lay summary This is the first study to directly compare the signaling properties of the 3 major types of pigments: carotenoids, melanins, and pterins. While there have been many studies examining melanin and carotenoid, few studies have examined the signaling properties of pterins. In bluefin killifish, melanin predicts dominance and mating, whereas carotenoid and pterin predict health and mating. The elaborate colors used by male killifish potentially provide multiple messages to multiple receivers.Male bluefin killifish (Lucania goodei) exhibit extensive color variation in their fins, but the utility of this variation has not yet been determined. We collected males from multiple populations and spectrophotometrically determined the pigment types responsible for fin coloration. We determined that the orange coloration in the caudal fin is caused by carotenoid pigmentation. In contrast, color in the anal fin is either pterin based (yellow and red) or structural (blue) with a melanic fin border. As these colors have different developmental origins, the potential for complex signaling is high. Therefore, we sought to determine whether behavior, reproductive success, or health correlated with pigmentation. Males with more melanin on the anal fin were more dominant and had higher spawning success. Male-male aggression was greater between males with similar-sized melanic borders, indicating that melanic markings function as badges of status between males. Caudal carotenoid pigmentation did not correlate with dominance, but this highly labile ornament was correlated with body condition, parasite infection, and spawning success, suggesting a role in intersexual selection by signaling health to potential mates. Similar results were found for caudal fin coloration using digital photography. Pterin pigmentation in the anal fin was not related to dominance but was related to overall spawning levels and parasite infection, suggesting that pterin pigmentation may also signal immune status. Thus, the coloration of male bluefin killifish provides multiple messages to multiple receivers through these 3 pigments (melanin, pterin, and carotenoid) that have distinct developmental origins.