Mechanisms for color convergence in a mimetic radiation of poison frogs

In animals, bright colors often evolve to mimic other species when a
resemblance is selectively favored. Understanding the proximate mechanisms
underlying such color mimicry can give insights into how mimicry evolves,
for example, whether color convergence evolves from a shared set of
mechanisms or through the evolution of novel color production mechanisms.
We studied color production mechanisms in poison frogs (Dendrobatidae),
focusing on the mimicry complex of Ranitomeya imitator. Using reflectance
spectrometry, skin pigment analysis, electron microscopy, and color
modeling, we found that the bright colors of these frogs, both within and
outside the mimicry complex, are largely structural and produced by
iridophores, but that color production depends crucially on interactions
with pigments. Color variation and mimicry is regulated predominantly by
iridophore platelet thickness and, to a lesser extent, concentration of
the red pteridine pigment drosopterin. Compared to each of the four morphs
of model species which it resembles, R. imitator displays greater
variation in both structural and pigmentary mechanisms, which may have
facilitated phenotypic divergence in this species. Analyses of non-mimetic
dendrobatids in other genera demonstrate that these mechanisms are
widespread within the family, and that poison frogs share a complex
physiological “color palette” that can produce diverse and highly
reflective colors.