Migration and selection can be used interchangeably in models. It
is therefore important to make better estimates of migration and to
explore the question of non-visual fitness difference. As the melanics
disappear, field studies on morph frequency change become increasingly
difficult. With respect to migration, it would be possible to
conduct further release and recapture trials. Tighter indirect estimates
of gene flow, encompassing adult and larval stages, using a large panel
of markers would also be useful. Adult females fly less than males.
Comparison of the pattern of genetic isolation by distance for
unlinked autosomal loci (for example, Daly et al., 2004) versus
mitochondrial or W-chromosome-linked loci could in principle
detect dispersal differences between adult males and females.
A key outstanding question that has emerged from the recent
molecular studies is the depth of phylogenetic conservation of the
developmental regulator underlying the carbonaria mutant. We know
that United Kingdom carbonaria is the result of a recent mutation
event, but the existence of similar melanic phenotypes in other
B. betularia populations (continental Europe and North America) and
many other moth species suggests an ancestrally conserved mechanism.
If this turns out to be true, it will be easier to explain the
phenomenon of industrial melanism in moths, although not necessarily
why such a ‘hotspot’ for melanism exists, given that insect
melanism has several potential switches.