Discovering the mutational events that fuel adaptation to environmental change remains an important challenge for evolutionary biology. The classroom example of a visible evolutionary response is industrial melanism in the peppered moth (Biston betularia): the replacement, during the Industrial Revolution, of the common pale typica form by a previously unknown black (carbonaria) form, driven by the interaction between bird predation and coal pollution1. The carbonaria locus has been coarsely localized to a 200-kilobase region, but the specific identity and nature of the sequence difference controlling the carbonaria–typica polymorphism, and the gene it influences, are unknown2. Here we show that the mutation event giving rise to industrial melanism in Britain was the insertion of a large, tandemly repeated, transposable element into the first intron of the gene cortex. Statistical inference based on the distribution of recombined carbonaria haplotypes indicates that this transposition event occurred around 1819, consistent with the historical record. We have begun to dissect the mode of action of the carbonaria transposable element by showing that it increases the abundance of a cortex transcript, the protein product of which plays an important role in cell-cycle regulation, during early wing disc development. Our findings fill a substantial knowledge gap in the iconic example of microevolutionary change, adding a further layer of insight into the mechanism of adaptation in response to natural selection. The discovery that the mutation itself is a transposable element will stimulate further debate about the importance of ‘jumping genes’ as a source of major phenotypic novelty3.
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The typica 1 haplotype (b–d interval) reference sequence has been deposited in GenBank under accession number KT182637; The B. betularia whole genome sequence has been deposited in the NCBI SRA database under accession number SRX1060178; the cortex splice variants have been deposited in GenBank under accession numbers KT235895– KT235906; Rps3A has been deposited in GenBank under accession number JF811439; α-spec has been deposited in GenBank under accession number KT182638.
The University of Liverpool Centre for Genomic Research (M. Hughes, C. Bourne, R. Eccles, C. Hertz-Fowler and J. Kenny) performed next-generation sequencing and Fragment Analyzer measurements. L. Cook directed us to historical data sources. C. Bergman advised on transposon detection. Population genetics simulations were performed on the University of Liverpool Advanced Research Computing Condor service. This work was supported by Natural Environment Research Council grants NE/H024352/1 and NE/J022993/1.
Extended data figures
Extended data tables
This table shows polymorphisms in the carbonaria candidate region.
This table contains polymorphisms in the locus b-d region.
This table contains Carbonaria morph frequencies in the Manchester area.
This table contains PCR primers for cortex, control genes and candidate genes.
This table contains sources, including accession numbers, for cortex and Fizzy family sequences.