A powerful way to study mechanisms that generate biodiversity is to focus on instances of convergent evolution. Convergent evolution occurs when the same trait evolves independently two or more times, providing natural replicates of adaptive evolution. For example, feeding on nectar and its accompanying morphological adaptations (e.g., long tapered bills with specialized tongue structures) have evolved independently in hummingbirds in North and South America, and in the sunbirds, spiderhunters, and flowerpeckers of Africa, Asia, and Australasia. This project will study these two groups of birds to better understand the ecological and genetic factors that lead to convergent evolution in associated genes and physiology. The research will investigate convergent evolution in the ability to taste sugar, metabolize alcohol, and live at high altitudes where there is less oxygen. It will also study convergence in the microbial communities living in the guts of the birds. This study will reveal how often the same genetic changes are responsible for the evolution of functionally similar physiological traits, and will lead to an improved understanding of adaptation and species diversification. The research will result in comprehensive evolutionary trees for hummingbirds, sunbirds, spiderhunters, and flowerpeckers, which will be an important resource for the conservation of these diverse avian groups that together constitute ~5% of bird species diversity. This project will train three graduate students and a postdoctoral fellow in research techniques integrating bioinformatics, functional physiology, behavioral ecology, genetics, and phylogenetics. It will also train up to ten undergraduates in sophisticated molecular genetic techniques and physiological research, which will give them valuable research experience. This grant will promote public understanding of science through a collaboration with educators who run the "Understanding Evolution" website, who will help to develop course materials for teachers that explain evolutionary concepts like adaptation and convergent evolution in the context of the diversification of hummingbirds and sunbirds.

This project will study convergence in traits that improve hypoxia resistance, convergence in traits related to nectarivory, and will investigate how traits related to nectarivory may converge in high-altitude environments that characterize the diversification of hummingbirds and sunbirds. On the genetic level, the research team will study genes related to nectarivory (i.e., sugar taste receptors, alcohol metabolism genes) and gene pathways that can confer hypoxia resistance (i.e., hemoglobin, OXPHOS, and hypoxia-inducible factor pathways). In addition, the researchers will sequence 16S ribosomal RNA genes from gut samples of nectarivorous birds to study microbial communities. On the functional level, the research team will test how genetic changes have altered phenotypes important for both organismal function and subsequent diversification into new ecological niches. To accomplish this, the team will perform physiological tests to measure hypoxia resistance, quantify dietary alcohol exposure (in the form of fermented nectar) from feather samples, predict metabolic functions of gut microbes from their 16S rRNA sequences, assay functional differences among genetic variants in the lab (e.g., cell-culture assays that measure responsiveness of different taste receptor variants), and conduct behavioral tests of taste discrimination abilities. On the phylogenetic level, the research team will study the evolutionary history of genes and phenotypes to reveal instances of convergent evolution within and between the two avian radiations. Finally, the team will integrate all genetic, functional, and phylogenetic data to evaluate: (1) how the prevalence of convergent genetic evolution changes with time, and (2) how suites of traits co-evolve in response to high-altitude environments.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Leslie J. Rissler
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University of California Berkeley
United States
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