Overview
This lecture covers experimental evolution, highlighting its methods, core findings, and applications in adaptation, sexual selection, and resistance, with examples from bacteria, mites, beetles, mice, and algae.
Introduction to Experimental Evolution
- Experimental evolution studies evolutionary processes in controlled environments over observable timescales.
- Differs from artificial selection; traits evolve in response to experimental conditions, not intentional human selection.
- Early example: William Dallinger evolved bacteria to survive higher temperatures over seven years.
Advantages of Experimental Evolution
- Allows precise control over environmental and genetic variables.
- Enables replication, so multiple experimental populations can be compared.
- Ancestral and derived populations can be directly compared for fitness and traits.
Long-Term Experiments: E. coli Case Study
- Richard Lenski’s E. coli experiment started in 1988 with 12 genetically identical populations.
- Populations are periodically frozen, enabling time travel to past generations.
- Adaptation is measured by relative fitness and cell size, showing continued adaptation even after 50,000 generations.
- Some lines evolved higher mutation rates, leading to faster adaptation.
- Evolution can show punctuated equilibria: long periods of stasis interrupted by sudden changes.
- Historical contingency: certain mutations must occur first before new traits, like citrate metabolism, can evolve.
Sexual Selection Explored Experimentally
- Sexual selection can purge deleterious mutations, demonstrated in mites and dung beetles.
- Studies show enforced polyandry (multiple mates) increases fertility and viability compared to enforced monogamy (single mate).
- Experiments in fruit flies and mice reveal that selection for mating success correlates with lower mutation load and improved reproductive traits.
Experimental Evolutionary Ecology & Resistance
- Environmental complexity affects trait evolution, as shown in mite habitat experiments.
- Evolution of resistance studied using fast-replicating algae under various herbicide regimes, revealing genetic correlations in resistance traits.
- Experimental evolution can inform agricultural and medical practices, such as managing herbicide or antibiotic resistance.
Criticisms and Limitations
- Laboratory environments are artificial and may not fully mimic natural conditions.
- Microbial evolution may not directly scale up to explain evolution in larger, slower-reproducing organisms.
Key Terms & Definitions
- Experimental Evolution — Study of evolutionary processes under controlled, repeatable laboratory conditions.
- Artificial Selection — Human-directed breeding for specific traits.
- Historical Contingency — The dependence of evolutionary outcomes on specific prior events or mutations.
- Punctuated Equilibrium — Pattern of evolutionary change involving long periods of little change interrupted by brief periods of rapid evolution.
- Polyandry — Female mating with multiple males, increasing sexual selection.
- Fitness — Relative genetic contribution of an organism to future generations.
Action Items / Next Steps
- Consider reading references provided by the lecturer for deeper understanding.
- Explore opportunities for honors projects or research in experimental evolution labs.
- Review data and methods from Lenski’s E. coli experiment and similar studies.