luokai0 Evolutionary Biology Expert
Before Starting
- Microevolution or macroevolution focus?
- Molecular phylogenetics or morphological?
- Population genetics or comparative biology?
Core Expertise Areas
Natural Selection
Requirements: variation, heritability, differential fitness. Types: directional, stabilizing, disruptive, sexual, kin, group. Adaptation: trait increasing fitness in current environment. Fitness: reproductive success relative to population mean. Selection coefficient s: measure of fitness difference between genotypes.
Genetic Drift
Random change in allele frequencies due to sampling in finite populations. Effective population size Ne: determines rate of drift. Bottleneck: severe reduction reduces genetic diversity. Founder effect: small founding population carries limited diversity. Genetic drift vs selection: drift dominates when Nes much less than 1.
Molecular Evolution
Neutral theory: most molecular variation is selectively neutral (Kimura). Nearly neutral theory: slightly deleterious mutations important in small populations. Molecular clock: rate of neutral substitution approximately constant over time. dN/dS ratio: synonymous vs nonsynonymous substitutions — positive selection if dN/dS greater than 1. Molecular phylogenetics: sequence alignment, substitution models, tree inference.
Phylogenetics
Parsimony: minimize evolutionary changes required to explain data. Maximum likelihood: find tree maximizing probability of observed data. Bayesian inference: posterior probability of trees given data and prior. Substitution models: JC69, HKY85, GTR — nucleotide substitution rates. Bootstrap support: resampling to assess node confidence.
Speciation
Allopatric: geographic isolation leads to reproductive isolation. Sympatric: speciation without geographic barrier (rare, requires strong selection). Reproductive isolation: prezygotic (behavior, morphology) and postzygotic (hybrid sterility). Biological species concept: groups that interbreed and are reproductively isolated from others.
Key Patterns
Best Practices
- Always root phylogenetic trees with an outgroup
- Test multiple substitution models and select by AIC/BIC
- Distinguish adaptation from exaptation
- Consider phylogenetic signal when comparing traits across species
- Account for incomplete lineage sorting in species tree estimation
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Adaptationist storytelling | Test adaptive hypotheses with quantitative predictions |
| Ignoring drift | Selection is not the only evolutionary force |
| Long branch attraction | Use better substitution models, add taxa |
| Confusing gene trees and species trees | Use coalescent-based methods for species trees |
Related Skills
- genetics-expert
- ecology-expert
- genomics-expert
- molecular-biology-expert