THE GENETICS OF WING PATTERN ELEMENTS IN THE POLYPHENIC BUTTERFLY, BICYCLUS-ANYNANA

The tropical butterfly, Bicyclus anynana, is highly polyphenic in response to seasonal changes (temperature and rainfall) in Malawi. The wing pattern varies considerably between the wet and dry season forms, particularly with respect to the background colour and the size of many of the wing pattern elements (e.g. eyespots). A selection experiment was carried out to determine the heritability of one of the ventral wing surface eyespots. The degree of genetic covariation among the various polyphenic ventral surface pattern elements and two non-polyphenic dorsal surface eyespots was also investigated. Selection to both increase and decrease the relative size of the second eyespot on the ventral surface was successful and indicated a heritability of more than 0.4. Other eyespots and the transverse wing band on the ventral surface all showed correlated responses. On the dorsal surface only the second eyespot showed a correlated response to selection. The results indicate that response to selection occurred at two levels: (i) the genes affecting the size of the eyespot directly and (ii) the eyespot biochemical determination mechanism. The fact that not all of the dorsal surface features showed correlated responses suggests that subtle differences may exist between the ways in which the production of eyespots on the ventral and dorsal surface is controlled.