Peppered Moth Evolution - Rise and Fall of Phenotype Frequency

Rise and Fall of Phenotype Frequency

Melanism has appeared in the European and North American peppered moth populations. Information about the rise in frequency is scarce. Much more is known about the subsequent fall in phenotype frequency, as it has been measured by lepidopterists using moth traps.

Though a black peppered moth was found in 1811, this can be seen as an aberrant morph caused by a recurrent mutation that was probably selected out of the population. The first carbonaria to be found was caught in Manchester, England in 1848, but was only reported 16 years later in 1864 by Edleston. Edleston notes that by 1864 it was the more common morph in his garden in Manchester. Steward compiled data for the first recordings of the peppered moth by locality, and deduced that the carbonaria morph was the result of a single mutation that subsequently spread. By 1895, it had reached a reported frequency of 98% in Manchester.

From around 1962 to the present, the phenotype frequency of carbonaria has steadily fallen. Its decline has been measured more accurately than its rise, because of more rigorous scientific studies being conducted. Notably, Bernard Kettlewell conducted a national survey in 1956, Bruce Grant conducted a similar one in early 1996., and L.M. Cook in 2003.

Similar results were found in America. Melanic forms have not been found in Japan. It is believed that this is because peppered moths in Japan do not inhabit industrialised regions.