Microstructures amplify carotenoid plumage signals in tanagers

Area of Science:

• Evolutionary biology
• Animal coloration
• Sexual selection

Background:

• Carotenoid-based plumage colors are often considered honest signals of an individual's condition.
• Sex differences in feather pigments and microstructures that produce coloration are not fully understood.
• Tanagers (Ramphocelus) exhibit striking sexual dimorphism in plumage color.

Purpose of the Study:

• To investigate the drivers of male-female color differences in the tanager genus Ramphocelus.
• To determine the relative roles of feather pigments and microstructures in producing plumage coloration.
• To test whether carotenoid pigments alone explain the observed color dimorphism.

Main Methods:

• Spectrophotometry was used to quantify feather color.
• Liquid chromatography-mass spectrometry (LC-MS) analyzed pigment profiles.
• Scanning electron microscopy (SEM) and finite-difference time-domain (FDTD) optical modeling examined feather microstructures.

Main Results:

• Males exhibited significantly more saturated plumage than females.
• Carotenoid pigment profiles were largely concordant between sexes.
• Elaborate feather microstructures in males, absent in females, amplified color saturation and generated specific hues like 'super black' and 'velvet red'.

Conclusions:

• Feather microstructures, rather than carotenoid pigments, are the primary drivers of male-female color differences in Ramphocelus tanagers.
• The evolution of microstructural amplifiers may allow males to enhance appearance independently of quality.
• Carotenoid-based honesty indices may not fully explain the evolution of male plumage coloration.