however, much evidence supports that a single event colonization is the best explanation. one theory of nearctic colonization states that the reason for the colonization was a larva host plant shift. the position of the poplar admiral ("l. populi"), a palearctic species, in a phylogenetic tree confirms that the poplar is the closest existing relative of the nearctic taxa and is consistent with the theory that the host plant had a large effect on the evolution of north american admirals. just like the wing-pattern of the palearctic butterflies has little evidence of divergence, the host plant use of these species also shows no sign of divergence. these species only feed on different species of honeysuckle ("lonicera" ssp.) the exception is the poplar that feeds exclusively on aspen ("populus tremulus" of the willow family). all north american "limenitis" feed on members of the willow family as well, suggesting that an (ancestral host plant shift) expansion of a novel host plant across the bering land bridge could have driven the colonization of the nearctic. species level phylogenies based on the mitochondrial gene coi and the gene efi-α of nearctic and palearctic species also indicate a single colonization of the nearctic species. the phylogenies produced indicate that a white-banded ancestor similar to the species "l. arthemis". established itself in north america and resulted in several major lineages, three of which involved mimicry independently of each other. given the present monophyly of the nearctic species, it is likely that a single migration and subsequent expansion of the population was the foundation of the nearctic butterflies.