The relationship between mimetic imperfection and phenotypic variation in insect colour patterns.

Many hoverflies (Syrphidae) mimic wasps or bees through colour or behavioural adaptations. The relationship between phenotypic variation in colour pattern and mimetic perfection (as determined by pigeons) was investigated in three species of Müllerian mimics (Vespula spp.) and 10 Batesian hoverfly mimics, plus two non-mimetic species of flies. Four predictions were tested: (i) Batesian mimics might be imperfect because they are in the process of evolving towards perfection, hence there should be a positive relationship between variation and imperfection; (ii) some Batesian mimics are imperfect because they do not have the appropriate genetic variation to improve and have evolved to be as good as possible, hence there should be no differences between species, all displaying a low level of variation; (iii) very common hoverflies should show the highest levels of variation because they outnumber their models, resulting in high predation and a breakdown in the mimetic relationship; and (iv) social wasps (Vespula) have such a powerful defence that anything resembling a wasp, both Müllerian and perfect Batesian mimics, would be avoided, resulting in relaxed selection and high variance. Poor mimics may still evolve to resemble wasps as well as possible and display lower levels of variation. The data only provided support for the fourth prediction. The Müllerian mimics, one of the most perfect Batesian mimics, and the non-mimetic flies displayed much higher levels of variation than the other species of Batesian mimics.