THE GENETICS OF PHENOTYPIC PLASTICITY IN ADULT ABDOMINAL COLOR PATTERN OF ERISTALIS-ARBUSTORUM (DIPTERA, SYRPHIDAE)

The abdominal colour pattern of Eristalis arbustorum is a plastic char acter which is heavily influenced by developmental temperature. The pr esent study investigated the form of the reaction norms of amount of a bdominal yellow and intensity of the yellow (measured as grey value) o n pupal development temperature. The slope of the reaction norm for am ount of yellow was steeper in males than in females. The reaction norm s for grey value on temperature were nonlinear. Family groups were rea red to enable a consideration of the genetics to be made. There were s ignificant family by environment interactions for both characters for both sexes indicating genetic variance for plasticity. Pupal developme nt time is closely correlated with developmental temperature. The rela tionship between amount of yellow on the abdomen and log pupal develop ment time was curvilinear and fitted a quadratic function well. There was significant among-family variation in the slopes of these lines fo r females, but not for males, again suggesting genetic variation for p lasticity. The results are discussed in relation to the maintenance of genetic variation.