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Parallel Molecular Evolution in Pathways, Genes, and Sites in High-Elevation Hummingbirds Revealed by Comparative
Marisa C W Lim1, Christopher C Witt2, Catherine H Graham1,3
1Department of Ecology and Evolution, Stony Brook University.
Genome Biology and Evolution
|May 23, 2019
Summary
High-elevation hummingbirds show parallel evolution in cellular respiration and metabolism pathways due to environmental pressures. However, independent lineages rarely share the exact same genetic changes for adaptation.
Area of Science:
- Evolutionary Biology
- Molecular Evolution
- High-Altitude Adaptation
Background:
- High-elevation environments present unique challenges like low oxygen, cold, and high UV radiation.
- These shared challenges may drive similar genetic adaptations across different species (parallel evolution).
- Hummingbirds (Trochilidae) in the Andes offer a model system with multiple independent high-elevation transitions.
Purpose of the Study:
- To investigate parallel molecular evolution in Andean hummingbird species at high elevations.
- To identify specific biochemical pathways, genes, and sites under positive selection.
- To understand the role of elevation thresholds in detecting adaptive genetic changes.
Main Methods:
- Phylogenetic analysis of 12 Andean hummingbird species.
- Comparative genomic analysis to detect positive selection across elevation gradients.
- Examination of gene functions and pathways, including cellular respiration, metabolism, and cell death.
- Testing different elevation cutoffs (>1,500m vs. >2,500m) to define high-elevation categories.
Main Results:
- Evidence of parallel evolution in several biochemical pathways and genes across high-elevation hummingbird species.
- Positively selected genes were predominantly involved in cellular respiration, metabolism, and cell death.
- While pathways and functions were similar across different elevation thresholds, specific genes under selection rarely overlapped.
- The gene EPAS1 (HIF2α) showed positive selection only when high-elevation was broadly defined (>1,500m).
Conclusions:
- A few biochemical pathways and genes predictably evolve during hummingbird adaptation to high-elevation.
- Despite convergent functional adaptation, independent hummingbird lineages seldom utilize the same specific genetic substitutions.
- The definition of elevation categories can influence the detection of specific genes under selection.
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