The evolution of carotenoid‐based plumage colours in passerine birds

Abstract

Many birds use carotenoids to colour their plumage yellow to red. Because birds cannot synthesise carotenoids, they need to obtain these pigments from food, although some species metabolise dietary carotenoids (which are often yellow) into derived carotenoids (often red). Here, we study the occurrence of yellow and red carotenoid‐based plumage colours in the passerines, the largest bird radiation and quantify the effects of potential ecological and life‐history drivers on their evolution. We scored the presence/absence of yellow and red carotenoid‐based plumage in nearly 6,000 species and use Bayesian phylogenetic mixed models to assess the effects of carotenoid‐availability in diet, primary productivity, body size, habitat and sexual selection. We also test the widespread assumption that red carotenoid‐based colours are more likely to be the result of metabolization. Finally, we analyse the pattern of evolutionary transitions between yellow and red carotenoid‐based plumage colours to determine whether, as predicted, the evolution of yellow carotenoid‐based colours precedes red. We show that, as expected, both colours are more likely to evolve in smaller species and in species with carotenoid‐rich diets. Yellow carotenoid‐based plumage colours, but not red, are more prevalent in species that inhabit environments with higher primary productivity and closed vegetation. In general, females were more likely to have yellow and males more likely to have red carotenoid‐based plumage colours, closely matching the effects of sexual selection. Our analyses also confirm that red carotenoid‐based colours are more likely to be metabolised than yellow carotenoid‐based colours. Evolutionary gains and losses of yellow and red carotenoid‐based plumage colours indicate that red colours evolved more readily in species that already deposited yellow carotenoids, while the reverse was rarely the case. Our study provides evidence for a general, directional evolutionary trend from yellow to red carotenoid‐based colours, which are more likely to be the result of metabolization. This may render them potentially better indicators of quality, and thus favoured by sexual selection.

To colour a bird: The evolution of carotenoid‐based colouration in passerines is shaped by sexual selection, ecology and life history

“…Delhey et al (2022) collated a vast dataset including plumage colouration, carotenoid dietary content, and ecological variables from various databases and previous studies. The authors then analysed these data to reveal broad evolutionary patterns addressing three main questions.…”

“…et al, 2004). InDelhey et al (2022), body size was negatively correlated with the evolution of carotenoid-based colouration. While evidence for environmental limitation does not necessarily imply that carotenoid-based colouration signals foraging ability, the work byDelhey et al (2022) draws renewed attention to the roles of ecology and life history on the macroevolution of sexually selected signals.…”

“…In birds, it is largely assumed that yellow colouration is produced by carotenoid deposition in feathers, with little or no chemical modification, whereas red colouration requires multiple metabolic reactions of the dietary carotenoids (Prum et al, 2012). Delhey et al (2022) examined the length of metabolic pathways leading to yellow and red colouration and confirmed that red colouration more often requires metabolically derived pigments.…”

“…Mahler et al, 2003), or conducted family-level analyses, bearing limited phylogenetic resolution (Olson, 2006). A recent study by Delhey et al (2022) investigates enduring question about the evolution of carotenoid-based pigmentation, using a species-level phylogeny of passerines, the largest bird radiation worldwide.…”

“…Nonetheless, the results of this study suggest that the rate at which carotenoids can be consumed is perhaps even more important than environmental availability. Due to their higher metabolic rate, smaller birds ingest more food relative to their body mass, which may explain why smaller birds have higher levels of carotenoids circulating in their blood (Tella F I G U R E 1 Schematic overview of some of the main results in Delhey et al (2022). (a) Red carotenoid-based pigmentation in passerines is likely to originate after yellow carotenoid deposition has evolved, with the former colouration being more metabolically derived.…”