ANCESTRAL STATE RECONSTRUCTION OF MIGRATION: MULTISTATE ANALYSIS REVEALS RAPID CHANGES IN NEW WORLD ORIOLES (ICTERUS SPP.)

Abstract

During the past century, numerous theoretical articles explored the evolution of seasonal migration in birds; many of these focused on environmental or social conditions that may have led to the origin of migration. More recent work has focused not on the origin of migration, but on changes in migratory behavior that have occurred in modern species and their immediate ancestors. We used a novel approach, a multistate ancestral state reconstruction of migration, to examine patterns of migratory evolution in the New World orioles (Icterus spp.). Both the multistate and binary reconstructions indicated repeated gains in migration. However, the multistate method revealed details of how migration may be gained that the standard binary-state reconstructions would not have shown. Our maximum-likelihood reconstruction, using branch lengths based on a molecular phylogeny, suggested multiple instances of rapid gain of migration. Furthermore, we found that every migratory species’ migration type diff ered from that of its closest relatives. Surprisingly, no partially migratory species was closely related to a fully migratory species. These novel patt erns involving gain of migration demonstrate the utility of multistate ancestral reconstruction for examining changes in migratory behavior in closely related birds.