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 Stoll) with typical coloration were more successful in intrasexual competition for mating territories than were males altered to have female-like mimetic coloration. Sibling males were matched for wingspan and emergence date and released as pairs, one with its pattern altered and one a control that was marked but with unaltered appearance. Significantly fewer altered males were resighted one or more days after release compared with control males (33% vs. 76%, 1990; 46% vs. 83%, 1993). Altered males were less able to establish and maintain themselves in preferred territories. The inability of released, altered males to establish a territory appears related to significantly longer male-male encounters. Encounters involving at least one participant with altered appearance averaged 66 s compared with 24 s if neither male was altered. However, altering the coloration of P. polyxenes males that already had established themselves in a territory had little effect. After courtships of similar duration (≈ 40 s), released virgin females were equally likely to mate with either altered or control males. This suggests that male-male intrasexual selection is of greater importance than female mate choice in maintaining a non-mimetic dorsal coloration in male P. polyxenes. © 1996 The Society for the Study of Evolution.