Genetic Diversity in Endemic Galápagos Birds: Patterns and Implications

Due to their smaller sizes and isolation, island populations generally have reduced genetic variability, which can have negative fitness consequences. The Galapagos Islands have played a unique and important role in our understanding of evolution, and the population genetics of bird species native to the islands is relatively well studied. Native Galapagos bird species exhibit a range of genetic patterns at neutral loci. For example, hawk and mockingbird population genetic variability is closely correlated with island size, demonstrating the effect of genetic drift, whereas gene flow has mitigated the effect of drift in dove and finch populations, resulting in higher genetic variability. Similarly, Galapagos seabirds exhibit a range of patterns, with some having greatly reduced variation compared to relatives outside of Galapagos (e.g., magnificent frigatebirds, penguins) and others having relatively high genetic variability (e.g., great frigatebirds). Published studies of major histocompatibility variability in hawks and penguins show a pattern of reduced variability at functional loci for Galapagos species compared to mainland congeners. Research has also demonstrated a relationship between genetic variability and fitness in some Galapagos species. Galapagos hawks have weaker innate immune function and higher louse loads than their more heterozygous mainland congener, and medium ground finches with higher heterozygosity are more likely to survive and breed. In contrast, no relationship between inbreeding and innate immune function or ectoparasite load was detected for mockingbirds. Further study of the population genetic dynamics of these species will continue to better inform management practices in the face of evolving threats.