The industrial melanism mutation in British peppered moths is a transposable element

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From: Nature(Vol. 534, Issue 7605)
Publisher: Nature Publishing Group
Document Type: Report
Length: 5,854 words
Lexile Measure: 1510L

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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 pollution (1). 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 unknown (2). 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 novelty (3).

Ecological genetics, the study of polymorphism and fitness in natural populations, has been revitalised through the application of next-generation sequencing technology to open up what were previously treated as genetic black boxes (4,5). Growing appreciation of the loci and developmental networks that generate adaptive phenotypic variation (6) promises to answer fundamental questions about the genetic architecture of adaptation, such as the prevalence of genomic hotspots for adaptation (7), the relative contributions of major- and minor-effect mutations (8), and the structural nature and mode of action of beneficial mutations (9). Characterizing the identity and origin of functional sequence polymorphisms provides the explicit link between the mutation process and natural selection. In this context, while industrial melanism in the peppered moth has retained its appeal as a graphic example of the spread of a novel mutant rendered favourable by a major change in the environment, the crucial piece of the puzzle that has been missing is the molecular identity of the causal mutation(s) (10).

A combined linkage and association mapping approach previously localized the carbonaria locus to a <400-kb region orthologous to Bombyx mori chromosome 17 [(loci b-d) (2). Thirteen genes and two microRNAs occur within this interval, none of which was known to be involved in wing pattern development or melanization. By extending the association mapping approach to a larger population sample and more closely spaced genetic markers (see Methods), we narrowed the carbonaria candidate region to about 100 kb (Fig. 1a). The candidate region resides entirely within the...

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Gale Document Number: GALE|A454485426