Variation and seasonal changes in hoverfly species: interactions between temperature, age and genotype

Abstract

Eristalis tenax L. and E. intricarius L. are two hoverflies which vary considerably in colour pattern. Whilst much of the phenotypic variation in both species is due to genetic variation at major gene loci, there are interactions with pupal temperature and with age of adult. Low pupal temperatures produce, on average, darker abdominal patterns in E. tenax, although the effect is hard to pick out in natural populations. Changes of pattern with age convert a bimodal autumn population to a unimodal post-hibernation population in the following spring. Hair colour is also made darker by cold treatment. Pupal treatments have a strong effect on hair colouration in E. intricarius. High temperatures inhibit the production of black hairs on the thorax, but not all the genotypes are equally sensitive to temperature. Seasonal fluctuations in colour pattern frequencies are detectable in E. intricarius. In three Eristalis species that have been studied so far, the interactions between genotype, age and temperature operate in quite different ways. The temperature responses may be relevant to theories of thermal melanism, although the colour pattern polymorphisms are, more obviously, examples of Batesian mimicry.