Artificial selection on the shape of reaction norms for eyespot size in the butterfly Bicyclus anynana: direct and correlated responses

The tropical butterfly Bicyclus anynana shows phenotypic plasticity in its ventral wing pattern as an adaptive response to wet-dry seasonality. Wet season form individuals have large eyespots, whereas individuals of the dry season generation have small eyespots. In the laboratory these forms can be Obtained by rearing larvae at high and low temperatures, respectively. To study the extent to which the shape of the nearly linear reaction norms for eyespot size can be changed we applied four generations of sib selection by rearing full-sib families across three temperatures. in addition, we measured ecdysteroid titres shortly after pupation in the final generation. Although phenotypic variation in shape was present initially, the experiment yielded lines with reaction norms with similar shapes but different elevations. High, positive genetic correlation across temperatures can explain this lack of response. Differences in ecdysteroid titres did not readily relate to differences in eyespot size.