Moths moths moths

Following on from yesterday's post about the peppered moth we have Industrial Melanism in British Peppered Moths Has a Singular and Recent Mutational Origin.

This paper follows on from the failure to pinpoint any of the usual suspects as responsible for the two alternative forms of this moth, mottled or black. By examining the offspring of matings between the two forms, the authors were able to home in on the region responsible. This DNA of this region was then sequenced and compared with the genome of the silkmoth. They found that this region corresponds to part of chromosome 17 in the silkmoth and the order of the genes along the chromosome is the same in both species. With some sequences of these genes in hand, the authors could now examine the differences between the two  forms of peppered moth more closely.

Moths were collected from across the UK for DNA analysis using 6 sites along the chromosome region suggested by genetics. The authors found that some of these sites showed statistically significant association with the wing pattern (peppered or dark). Because of the strong similarity of DNA sequences from the darker moths (compared to the much higher diversity among the typically patterned moths), the authors suggest that this form only arose once in Britain.

Having demonstrated that one region in particular is associated with the darker pattern, and that this darker pattern arose once, the next question is to look for a genetic cause, particularly in light of the failure of the candidate gene approach. By looking at the statistical associations among DNA sequence variants, it was possible to narrow the chromosomal region of interest to about 200,000 nucleotides (the 'letters' of DNA - A, T, G and C). This region is the peppered moth equivalent of a chromosomal region known to be important in butterfly wing patterning - the Bigeye region in the African butterfly Bicyclus anynana and a region known to be important in determining elements of the wing pattern in South American Heliconius butterflies.

These findings, together with the enormous amount of previous work on the peppered moth means that we can truly call this an icon of evolution: this one species of moth can tell us an almost unparalleled story about evolution. This is particularly relevant in the current context of climate change - the darker form of this moth arose once by a change in a genome region already known to be important in generating diversity in Lepidopteran wing patterns.