Lecture 9: Epigenetic Evolution

Question 1

What does this lecture talk about? the main theme/concepts, summarize?

Answer 1

1) This lecture emphasizes how phenotypic plasticity—the ability of an organism to change traits in response to its environment—can be a powerful driver of evolution. Epigenetic factors like Hsp90 support this process, potentially allowing for major evolutionary shifts. The lecture proposes that both Darwinian natural selection and environment-induced change have roles in shaping species over time, with epigenetics acting as a bridge between genetic evolution and environmental influence.

2) Lecture 9 explores “Epigenetic Evolution,” focusing on how the environment influences genetic and phenotypic evolution, deviating from the traditional model of Darwinian evolution.

Question 2

Darwinian vs. Lamarckian Evolution

Answer 2

1) Darwinian Evolution: Variation arises randomly through mutations, and natural selection acts on these traits. Extinction is common, and survival depends on “fitness” in a competitive environment.

2) Lamarckian Evolution: Proposed that environmental changes induce traits directly in response to need, leading to increasingly complex beings. Lamarck believed that organisms harmoniously adapt rather than compete.

Question 2

Microevolution ‘Standard Model’

Answer 2

1) Describes the flow from genome to phenome (visible traits) to population, community, and ecosystem.

2) Highlights developmental biases and modularity, emphasizing that both genome and phenome are organized in modular units that shape evolutionary outcomes.

Question 3

Epigenetic Landscape

Answer 3

Introduced by Conrad Waddington, this model visualizes gene expression as a landscape of “valleys” and “peaks.” Valleys represent stable developmental paths, or canalization, which buffers against minor genetic changes.

Question 4

Developmental Plasticity and Evolution

Answer 4

1) The concept that organisms can adapt traits in response to environmental pressures—known as phenotypic plasticity—which may later become genetically “fixed” through Darwinian processes.

2) Examples: Certain frogs, Daphnia, and zoo animals show adaptive traits under environmental stress that indicate a pathway where the environment influences gene expression in adaptive ways.

Question 5

Heat Shock Protein 90 (Hsp90)

Answer 5

Hsp90 acts as a stabilizer or “buffer” for development, concealing genetic variations unless environmental stress triggers change. When Hsp90 is inhibited, organisms like Drosophila and Arabidopsis exhibit hidden genetic traits, suggesting that environmental conditions can reveal latent diversity.

Question 6

Alternate Evolutionary Pathway

Answer 6

In contrast to traditional models, this approach suggests that phenotypic changes may come first, driven by environmental adaptation, which then leads to genetic changes—a process resembling “Lamarckian” ideas but validated by modern epigenetics.

Question 7

Evo-Devo-Eco Integration

Answer 7

This emerging framework incorporates evolutionary development (Evo-Devo) and ecology, emphasizing how development, phenotype, and environment intertwine. It highlights that phenotypic plasticity might have driven macroevolutionary change in early organisms.

Question 8

Polypterus as a Case Study

Answer 8

The fish Polypterus, with traits bridging aquatic and terrestrial life, exemplifies phenotypic plasticity. This “walking fish” adapts physically in lab settings, offering a model to study how terrestrial adaptation could have led to tetrapod evolution.