INTRASEXUAL SELECTION CONSTRAINS THE EVOLUTION OF THE DORSAL COLOR PATTERN OF MALE BLACK SWALLOWTAIL BUTTERFLIES, PAPILIO POLYXENES

Males of the eastern black swallowtail (Papilio polyxenes asterius Sto ll) with typical coloration were more successful in intrasexual compet ition for mating territories than were males altered to have female-li ke mimetic coloration. Sibling males were matched for wingspan and eme rgence date and released as pairs, one with its pattern altered and on e a control that was marked but with unaltered appearance. Significant ly fewer altered males were resighted one or more days after release c ompared with control males (33% vs. 76%, 1990; 46% vs. 83%, 1993). Alt ered males were less able to establish and maintain themselves in pref erred territories. The inability of released, altered males to establi sh a territory appears related to significantly longer male-male encou nters. Encounters involving at least one participant with altered appe arance averaged 66 s compared with 24 s if neither male was altered. H owever, altering the coloration of P. polyxenes males that already had established themselves in a territory had little effect. After courts hips of similar duration (approximate to 40 s), released virgin female s were equally likely to mate with either altered or control males. Th is suggests that male-male intrasexual selection is of greater importa nce than female mate choice in maintaining a non-mimetic dorsal colora tion in male P. polyxenes.