EVOLUTIONARY ORIGIN OF INSECT WINGS FROM ANCESTRAL GILLS

Two hypotheses have been proposed for the origin of insect wings. One holds that wings evolved by modification of limb branches that were al ready present in multibranched ancestral appendages and probably funct ioned as gills(1-5). The second proposes that wings arose as novel out growths of the body wall, not directly related to any pre-existing lim bs(6). If wings derive from dorsal structures of multibranched appenda ges, we expect that some of their distinctive features will have been built on genetic functions that were already present in the structural progenitors of insect wings, and in homologous structures of other ar thropod Limbs. We have isolated crustacean homologues of two genes tha t have wing-specific functions in insects, pdm (nubbin) and apterous. Their expression patterns support the hypothesis that insect wings evo lved from gill-like appendages that were already present in the aquati c ancestors of both crustaceans and insects.