Historical Specimens Reveal a Century of Genetic Change in Darwin's Finches

• Main Author: Farrington, Heather
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2011
• Subjects: Conservation; Conservation biology; Evolution & development; Evolution and Development; Genetics
• ISBN: 9781124595566; 1124595562

Understanding how populations change through time is critical in the generation of effective conservation biology practices. However, data from multiple time points, especially those that span a significant number of years/generations are rare. In this series of studies, I used a model system, Darwin’s finches of the Galápagos Islands, to investigate questions related to both long term and short term evolution in this system. These species are thought to be in a state of decline due to recent human-induced habitat disturbances, and increasing local extinction events. Darwin’s finches are also well-represented in museum collections. Therefore, this is an ideal system in which to study both change over time and extinction events in fragmented populations. I first used a traditional phylogenetics approach using multiple nuclear introns to examine the overall evolutionary history of this species radiation. These data generated a novel evolutionary tree topology, leading to the reevaluation of the earliest species divergences in this system. I then investigated short term evolutionary trends in warbler finch populations by utilizing genetic information (in the form of microsatellite markers) generated from museum specimens collected approximately 100 years ago. There was no genetic evidence of archipelago-wide population declines in the warbler finches. Both increases and decreases in genetic diversity were noted for individual populations. Decreases in genetic diversity were attributed to fluctuations in population size due to El Niño cycles, while increases were due to migration from other populations. On the island of Española, a suspected case of “genetic rescue”, when a population with low genetic diversity is infused with genetic variation through migration, was revealed. This suggests that migration may play an important role in maintenance of genetic diversity within island populations. Lastly, I again used museum specimens to compare extinct and extant populations to determine if there was any genetic indication of population declines prior to extinction events. In this rare test of the predictive ability of standing genetic variation to predict extinction risk, genetic diversity was generally equal to or greater than diversity in populations that have persisted through time. This result emphasizes the caution in using genetic data alone to monitor populations and evaluate extinction risk. All three studies yielded unexpected results, particularly those that utilized museum specimens from natural history collections. The overall conclusion of this dissertation highlights the importance of understanding population interactions in fragmented landscapes, which has major conservation implications for population persistence and viability.