Bio 9/4

Introduction

• Marine iguanas exemplify adaptations for survival in cold-water foraging conditions, with physiological limits on dive duration.

• Biologists study variation in populations and how natural selection acts on it to understand adaptations.

Key Concepts

• Variation: All populations exhibit variation in traits.

• Heritability: For natural selection, variation must be heritable.

• Adaptation: Traits like lung capacity, skin color, claws, and swimming ability are examples.

• Reproduction vs. Survival: Reproduction is the central currency of natural selection; survival often correlates but isn't always perfect.

• Trade-offs: Almost every adaptive trait involves a cost; adaptations are not perfection-agents.

Lamarck vs. Darwin

• Lamarckian idea: Organisms acquire traits during their lifetime and pass them on (e.g., stretching necks).

• Darwinian view: Existing variation in populations; individuals with advantageous traits reproduce more, passing those traits to offspring; favorable traits accumulate over generations.

Darwin's Observations and Inferences

• Observations: Variation among individuals; overproduction of offspring; many offspring fail to survive and reproduce.

• Inferences: Individuals with heritable traits enhancing survival/reproduction leave more offspring; favorable traits accumulate over time.

Population vs. Individual Level Selection

• Natural selection primarily acts at the individual level, where an individual's genotype interacts with the environment.

• "Good of the species" (group selection) is rare compared to individual-level selection.

Evidence and Examples of Evolution in Action

1. Artificial Selection: Selective breeding by humans demonstrates rapid trait shifts (e.g., dog breeds, Brassica vegetables).

2. Soapberry Bugs (Beak Size):

   • Beak length adapted to local fruit sizes in Florida populations, showing rapid evolution over less than 35 years.

   • Trade-off: Longer beaks require more energy, potentially reducing reproductive output if not advantageous for foraging.

3. Trinidad Guppies (Life-History Evolution):

   • Guppies adapt reproductive strategies (brood size, growth rate, size at reproduction) based on predator presence (above vs. below waterfalls).

   • Rapid evolution (30-60 generations) observed in field experiments when predator regimes changed.

4. Mutation and Natural Selection in Microbes (Antibiotic Resistance):

   • Bacteria rapidly evolve resistance to antibiotics through stepwise mutations under selective pressure.

   • Public Health Implications: Misuse or overuse of antibiotics in medicine and agriculture accelerates resistance, contributing to "superbugs" and disrupting microbiomes.

Additional Evidence for Evolution

• Homologous Traits: Shared ancestry (e.g., vertebrate forelimbs).

• Analogous Traits: Similar function due to convergent evolution, not shared ancestry.

• Embryonic & Molecular Homologies: Similarities in early development and conserved genes (e.g., Hox genes) across diverse species.

• Vestigial Structures: Remnants of ancestral features that have lost function (e.g., whale pelvic bones).

• Fossil Record & Transitional Forms: Evidence of historical change (e.g., Archaeopteryx).

• Biogeography: Geographic distribution of species reflecting continental drift and isolation (e.g., marsupials, endemic species like Darwin's finches).

• Birds and Dinosaurs: Birds are considered living dinosaurs.

Theoretical Foundations and Broader Implications

• A good scientific theory makes testable predictions and explains diverse observations.

• Natural selection acts on heritable variation; environmental changes drive new adaptations and can lead to speciation.

• Selection shapes life-history traits by influencing energy allocation between growth, survival, and reproduction.

Summary of Key Mechanisms and Terminology

• Variation: Heritable phenotypic differences.

• Adaptation: A trait increasing fitness.

• Natural Selection: Differential reproduction of individuals with specific heritable traits.

• Differential Reproduction: Core mechanism of selection.

• Directional Selection: Favors one extreme trait value.

• Trade-offs: Costs associated with adaptations.

• Artificial Selection: Human-directed breeding.

• Homology vs. Analogy: Shared ancestry vs. convergent similarity.

• Vestigial Structures: Remnants of ancestral traits.

• Fossils/Transitional Forms: Historical evidence.

• Endemism/Island Biogeography: Patterns of species distribution due to isolation.

• Malthusian Influence: Ideas on population growth and competition.

• Public Health and Evolution: Antibiotic resistance, malaria, vector control.

• Mathematical Models: Exponential growth ($N<em>t = N</em>0 e^{rt}$) and geometric growth ($N<em>t = N</em>0 <br>ightarrow N<em>{t+1} = ( ext{growth factor}) N</em>t <br>ightarrow N<em>t = N</em>0 <br>eq lambda^t$).