Evolution of resting behaviour in polymorphic ‘industrial melanic’ moth species

Abstract

The behaviour of individually marked melanic and typical forms of Allophyes oxyacanthae was followed in four successive tests in an apparatus comprising bark of three different reflectances. In samples of wild populations, melanics showed a moderate preference for dark bark, while typicals did not seem to prefer or avoid this substrate. However, in four of the eight families of known parentage tested, both melanics and typicals preferred to rest on dark bark. These four families were the progeny of dark typicals which had shown a preference for dark bark and were the families containing the darkest typicals. In A. oxyacanthae the variation in resting behaviour is not therefore closely associated with the melanic allele but may be linked to a ‘dark typical’ allele which, together with other loci, produces polygenic darkening of the normal phenotype. The results with A. oxyacanthae are compared with those obtained with Biston betularia and other moth species.