THE EVOLUTIONARY GENETICS AND DEVELOPMENTAL BASIS OF WING PATTERN VARIATION IN THE BUTTERFLY BICYCLUS-ANYNANA

We have studied interactions between developmental processes and genet ic variation for the eyespot color pattern on the adult dorsal forewin g of the nymphalid butterfly, Bicyclus anynana. Truncation selection w as applied in both an upward and a downward direction to the size of a single eyespot consisting of rings with wing scales of differing colo r pigments. High heritabilities resulted in rapid responses to selecti on yielding divergent lines with very large or very small eyespots. St rong correlated responses occurred in most of the other eyespots on ea ch wing surface. The cells at the center of a presumptive eyespot (the ''focus'') act in the early pupal stage to establish the adult wing p attern. The developmental fate of the scale cells within an eyespot is specified by the ''signaling'' properties of the focus and the ''resp onse'' thresholds of the epidermis. The individual eyespots can be env isaged as developmental homologues. Grafting experiments performed wit h the eyespot foci of the selected lines showed that additive genetic variance exists for both the response and, in particular, the signalin g components of the developmental system. The results are discussed in the context of how constraints on the evolution of this wing pattern may be related to the developmental organization.