THE REGULATION OF PHENOTYPIC PLASTICITY OF EYESPOTS IN THE BUTTERFLY BICYCLUS-ANYNANA

We use an outcrossed stock and selected lines of Bi-cydus anynana in c ombination with measurements and manipulations of ecdysteroid hormones in early pupae to examine the regulation of eyespot size in adult but terflies. The eyespots on the ventral wing surfaces express adaptive p henotypic plasticity in response to the dry-wet seasonal environments of the butterflies. Larvae reared at low or high temperatures produce adults with small or large ventral eyespots, respectively. Our experim ents examine the role of ecdysteroids in mediating this phenotypic pla sticity. Higher titers of ecdysteroids shortly after pupation yield la rger ventral wing eyespots. There is an uncoupling of the ventral eyes pots and those on the dorsal forewing.;The latter do not show phenotyp ic plasticity. They show very little response to rearing temperature, and variation in their size is not associated with differences in the dynamics of ecdysteroids in early pupae. A testable hypothesis in term s of the distribution of hormone receptors in the developmental ''orga nizers'' or foci of the eyespots is proposed to account for how some e yespots express plasticity while others do not.