Industrial melanism is a celebrated evolutionary phenomenon because it demonstrates the efficacy of natural selection in response to anthropogenic environmental change. We investigated a potential instance of industrial melanism in a vertebrate, the vermilion flycatcher (Pyrocephalus rubinus). The species is strikingly bright red throughout its broad range, but a sooty brown morph is abundant in the heavily polluted city of Lima, Peru. We found that plumage morph is perfectly predicted by a single nucleotide polymorphism in the MC1R gene. We quantified genotype and allele frequencies in seven neighborhoods of Lima. Within neighborhoods, there were fewer heterozygotes than expected, and surveys of mated pairs were consistent with assortative mating. The melanic allele frequency dropped from ~60% to ~5% across the urban-suburban interface, implicating strong divergent selection on plumage color. Spatial autoregressive models showed that coastal cloudiness predicted melanic allele frequency, while air pollution did not. We conclude that divergent selection and assortative mating act together to maintain the melanic allele at one extreme of a cloudiness gradient, even with no physical barriers to gene flow. The co-occurrence of industrial pollution and the melanic morph of the vermilion flycatcher is not industrial melanism, but a coincidence of human history and natural history
