Disseration Research for Marisa Lim: Molecular Basis of Hummingbird Distributions in the High Andes

This project will investigate the link between the distribution of hummingbird species across an elevational gradient in South America and the molecular basis of genetic adaptation to extreme conditions. We know that environmental variation effects the evolution and distribution of species. However, we do not know the molecular bases for how organisms adapt to this variation. A major challenge is to understand how molecular processes occurring in local populations relate to global species' distribution patterns over evolutionary time. This is difficult because evidence of adaptation can disappear over time, and because population genetic patterns can mimic adaptation. This project will compare several populations and species of Andean hummingbirds. Modern genetic methods will be used to measure natural selection on proteins while also taking account of population genetic structure. In addition, the project will include the training of high school and undergraduate students, and produce educational materials for genomic workshops. This project will bridge the gap between macroevolutionary distribution patterns and microevolutionary processes of adaptation. The goals are to test for genetic adaptation to high-altitude conditions in Andean hummingbird populations while controlling for demographic history, and to test for parallel evolution across populations that independently colonized the high Andes. Hummingbirds are an excellent system for studying genetic adaptation across altitudinal gradients. There are more than 300 species, they occur across a vast gradient - sea level to over 4000 meters - despite having the highest basal metabolic rates of any bird group, and there have been at least four independent colonization events of high-altitude habitats. The researchers will collect genomic data from 6-30 populations of two low and two high altitude species to test the hypothesis that adaptive changes in protein-coding genes shape altitudinal distributions in hummingbird populations that have recently colonized the high Andes. Researchers will use the genomic data to detect signatures of positive selection, an indicator of genetic adaptation, and measure population genetic structure across populations. The results of these analyses will provide critical insight into the mechanisms of colonization and adaptation to high elevation ecosystems.