Colonization of Galápagos Birds: Identifying the Closest Relative and Estimating Colonization

Native Galapagos bird species show varying colonization histories, with lineages representing a wide age distribution and various geographic origins. Of the taxa studied, founding lineages arrived from less than 300,000 years ago (e.g., Band-rumped Storm Petrel, hawk) up to 2.0–5.5 million years ago (e.g., dove, finches, mockingbirds). Some of these earlier lineages reached Galapagos before the youngest of the current islands formed, so they must have first colonized what are now the eastern islands. While the exact origin of colonizing lineages cannot always be determined, all the native land birds studied originated from the New World, where their closest living sister taxa breed. The closest related lineages to Galapagos seabirds are generally found elsewhere in the Pacific Ocean. Galapagos species vary in their diversification patterns post-colonization, with factors such as life history traits, island geology, and trade winds affecting the genetic patterns described. The mockingbirds and Darwin’s finches radiated into multiple species, while most others have not, probably due to high rates of gene flow (e.g., dove) or lack of time since colonization (e.g., hawks, warblers). Humans were responsible for the introduction of 12 bird species to Galapagos, as well as the introduction of invasive invertebrates, parasites, and pathogens, which pose a serious threat to native Galapagos fauna. Continued research into colonization histories and evolutionary units of native lineages will aid our understanding of host-parasite interactions and better inform conservation management decisions.