Peppered moth

Status: Secure species of night-flying moth notable for its evolution of peppered moth ecology (including a discussion of resting positions)

In Britain, the peppered moth is univoltine (i.e. it has one generation per year), whilst in south-eastern North America it is bivoltine (two generations per year). The Lepidopteran life cycle consists of four stages; ova (eggs), several larva instars (caterpillars), pupae and imagines (adults). During the day, the moths cryptically rest on trees, where they are predated by birds.

Genetics

Main article: peppered moth genetics

The are several melanic and non-melanic morphs. In Britain, the typical white speckled morph is known as f. typica, the melanic morph is f. carbonaria and the is f. insularia. These are controlled genetically. At present the biochemistry of the melanism remains unknown, though it should be possible for it to be elucidated.

Evolution

Main article: peppered moth evolution

The first carbonaria morph was recorded by Edleston in Manchester in 1848, and over the subsequent years it increased in frequency. This evolution was caused by natural selection (it is too fast to be due to genetic drift), though the increase was not monitored very effectively.

Predation experiments (see below) particularly by Bernard Kettlewell established that the agent of selection was birds who predated on the f. carbonaria morph.

The Clean Air Acts reduced levels of pollution, and typica morph frequency has increased, again by natural selection.

A similar process occurred in North America.

Predation experiments

Main Article: peppered moth predation experiments

Experiments to show differential bird predation in the wild have been conducted, notably by Bernard Kettlewell, who in 1953 and 1955 conducted classic experiments mark-release-recapture experiments. Later experiments have shown that was qualitatively correct.

Alternative theories

Main article: peppered moth alternative theories

Alternative theories to explain industrial melanism were proposed during the 1920s and 1930s. Particularly notable was the phenotypic induction hypothesis of J.W. Heslop-Harrison, who proposed that industrial pollutants could induce mutations in the peppered moth. The quality of the original science was poor.

Later some scientific dissenters have criticised the acceptance of the peppered moth story. In particular, Sargent et al (1998) argued for a developmental induction hypothesis, Cook, Grant and Majerus have all argued that Sargent et al's hypothesis does not fit the evidence.

Creationism

Main article: creationism and the peppered moth

Several people oppose the theory of evolution on religious grounds. From 1998 the traditional peppered moth story has been criticised. The scientific community remains unimpressed.

Further reading

The definitive reference on this work is Majerus' 1998 book Melanism: Evolution in Action, which provides an introduction to evolutionary theory as well as describing the peppered moth case study. There have been subsequent summaries by Cook [erm...], and Bruce Grant's can be downloaded here: