Introduction to Evolution and Natural Selection

ANNOUNCEMENTS

  • Announcements & Reminders

    1. Questions about lab practical?

    2. Learning Support Center Assignment due by 10/20

INTRODUCTION TO EVOLUTION

  • Reference: Chapter 22 of Campbell

Learning Objectives

  1. Describe the intellectual context of Darwin’s ideas, the observations he collected, and how they led to the idea of evolution by natural selection.

  2. Explain how natural selection works, including the focus on variation and the patterns of life which it explains.

  3. Explain the logic and give an example of each of these lines of evidence for evolution: direct observation, homology, fossil record, biogeography.

EVIDENCE FOR EVOLUTION

1. Direct Observation

  • Example: Clone USA300 - a virulent strain of methicillin-resistant Staphylococcus aureus (MRSA), known for causing "flesh-eating disease."

  • Video Reference: "A Future Without Antibiotics?" (0:00-3:00)

  • Clarification: The statement "Antibiotics have created drug resistance in MRSA" is misleading.

    • Historical Data:

    • 1945: 20% of S. aureus resistant to penicillin (~90% resistant now).

    • 1961: Emergence of methicillin resistance.

    • Present Day: Modern MRSA strains are resistant to many antibiotics.

MINI-QUIZ

Question 7

  • Which of these lines of evidence for evolution provides specific information about intermediate forms and approximate dates of evolutionary events?
    A. Direct observation
    B. Biogeography
    C. Fossil record
    D. Homology

Question 8

  • Considering the evolution of MRSA, predict what will happen as the new antibiotic “teixobactin” is applied to MRSA?
    A. MRSA will be completely eradicated because teixobactin is a new antibiotic.
    B. Some MRSA cells will be naturally resistant to teixobactin and will become more prevalent due to selection.
    C. Some MRSA cells will become resistant by evolving new genes in direct response to teixobactin.
    D. A new bacteria will evolve to take the place of MRSA.

INTRODUCTION TO EVOLUTION CONTINUED

  • Reference: Chapter 22 of Campbell

Learning Objectives

  1. Describe how cost/benefit analysis is used as a conceptual tool for understanding how natural selection optimizes traits of organisms.

  2. Explain how sexual selection shapes animals’ physical traits and mating behavior.

  3. Explain how kin selection shapes animal social behavior.

NATURAL SELECTION: PART 2

Conceptual Tool: Cost/Benefit Analysis

  • Each possible (behavioral) phenotype has its associated fitness benefits and fitness costs:

    • Optimal (behavioral) phenotype maximizes benefits while minimizing costs, expressed as:

    • B - C

  • Question: Which (behavioral) phenotype will be favored by natural selection?

SEXUAL SELECTION

Sexual Selection Explained

  • Definition: A form of natural selection where differences in reproductive success result from differences in mating success.

  • Questions Raised: Are these two different species of animal? Is the tail a product of natural selection, and what are its benefits and costs for male?

  • Sexual Dimorphism: An outcome of sexual selection where males and females exhibit different physical characteristics.

    • Male-specific traits and mating behavior optimized for male reproductive success:

    • Males produce inexpensive, abundant sperm.

    • Reproductive success limited by access to eggs.

    • Males compete for access to potential mates.

    • Female-specific traits and behaviors focus on resource availability and genetic fitness of potential mates:

    • Females produce expensive, scarce eggs.

    • Reproductive success limited by resources to produce eggs and genetic quality of sperm.

    • Females choose mates based on ability to provide resources and genetic fitness.

    • Question: Are males always the competitive sex? Are females always choosy?

MATING SYSTEMS

  • Degree of sexual dimorphism leads to classifications:

    • Competitive vs. choosy sex.

    • Types of mating bonds and parental care include:

    • Polygyny

    • Polyandry

    • Monogamy

  • Differential investment in offspring accounts for choosiness vs. competition among the sexes.

  • Types of Sexual Selection:

    • Intra-sexual selection (competition among the same sex).

    • Inter-sexual selection (mate choice).

INTRA-SEXUAL SELECTION

  • Definition: Competition between members of the same sex for mates involves:

    • Agonistic interactions.

    • Ritualized contests.

    • Dominance hierarchies.

    • Territoriality and interference.

    • Mate guarding strategies.

INTER-SEXUAL SELECTION

  • Definition: Members of one sex choose mates based on certain traits, including:

    1. Direct benefits (e.g., resources).

    2. Indirect (genetic) benefits (e.g., mate's genetic quality).

    3. Willingness to provide parental care.

    4. Influence of others' preferences on mate choices.

    • Example: Mate choice copying by female guppies (Poecilia reticulata).

MINI-QUIZ

Question 3

  • Female spotted sandpipers exhibit behaviors where they aggressively court males and leave the brood for males to incubate. These actions may repeat with multiple males until no males remain, which term best describes this behavior?
    A. Polygyny
    B. Polyandry
    C. Monogamy

Question 4

  • Which is an example of inter-sexual selection?
    A. Mate guarding
    B. Dominance hierarchies
    C. Nuptial gifts during courtship
    D. Sperm competition

KIN SELECTION

  • Definition of Altruism: Behaviors that reduce individual fitness but enhance the fitness of others.

  • Mechanism: Kin selection favors altruistic behavior as it enhances the reproductive success of genetic relatives.

  • Hamilton’s Rule: rB - C > 0

    • For altruistic behavior to be favored, the benefits relative to the costs must be positive.

    • Coefficient of Relatedness (r): Likelihood of shared alleles by descent, decreases with each meiotic event.

    • Kin selection's efficacy weakens as relatedness decreases.

INCLUSIVE FITNESS

  • Definition: Accounts for both direct fitness (own offspring) and indirect fitness (aid to relatives).

  • Equation:

    • ext{Inclusive fitness} = ext{direct (personal fitness)} + ext{indirect fitness}

MINI-QUIZ

Question 6

  • The theory of inclusive fitness states:
    A. There is no value to passing on your genes by reproducing.
    B. Helping any member of your species aids gene passing.
    C. Both producing own offspring and aiding relatives guarantees gene continuation.
    D. Advanced animals are more altruistic.

Question 5

  • Which relative has the highest coefficient of relatedness and is the most likely target of altruism?
    A. Cousin
    B. Niece
    C. Daughter
    D. Half sibling

EVOLUTION OF POPULATIONS

  • Reference: Chapter 23 of Campbell

Learning Objectives

  1. Define evolution from a population/genetic perspective (“microevolution”).

  2. Explain how to determine population evolution by comparing allele and genotype frequencies.

  3. Describe how natural selection, genetic drift, and gene flow cause (micro)evolution.

EVOLUTION DEFINED

  • Definition of Evolution: Change in allele frequencies in a population over generations.

  • Gene Pool: Collection of all alleles at all loci in a population.

NATURAL SELECTION CRITERIA

  • Natural selection occurs under the following conditions:

    1. Variation in traits among individuals within a population exists.

    2. Variation is heritable.

    3. Variation affects fitness concerning survival and reproduction.

HERITABLE VARIATION EXAMPLE

  • Example alleles:

    • W allele: (A^{CGTCA}) (orange pigment)

    • w allele: (A^{CTTCA}) (blue pigment)

  • Definitions:

    • Gene: A discrete unit of heredity info, a specific nucleotide sequence in DNA (~50kbp).

    • Allele: Versions of a gene producing distinguishable phenotypic effects.

    • Genotype: Genetic makeup of an organism.

    • Phenotype: Observable traits of an organism.

SEXUAL REPRODUCTION & VARIATION

  • Sexual reproduction generates genetic diversity through:

    1. Random fertilization.

    2. Independent assortment during gametogenesis.

    3. Crossing over during gametogenesis.

  • Each organism has unique phenotypic and genotypic traits due to these mechanisms.

SPECIES vs. POPULATION

  • Population: Group of individuals of the same species living in the same area and interbreeding.

  • Species: Group of populations potential to interbreed and produce viable offspring.

  • Gene Pool: The sum of all alleles at all loci in every individual of a population.

MUTATIONS IN EVOLUTION

  • Role of Mutation: Introduces new genetic variants (alleles).

  • Types of Mutations:

    • Base-pair substitutions.

    • Base-pair insertions.

    • Base-pair deletions.

  • Estimate: 50-100 new base substitutions per generation; 1-2 occur in protein coding regions (Gluckman et al. 2018).

SOURCE OF HERITABLE VARIATION

  • Ultimate Source:

    • D. Mutation (new alleles from replication errors).

HERITABLE VARIATION EXAMPLES IN QUIZ
Question 2

  • Source of new heritable variation?
    A. Sexual reproduction
    B. Gene flow
    C. Selection
    D. Mutation

Question 1

  • Which is NOT heritable genetic variation?
    A. Two-base-pair deletion in a coding region
    B. One-base-pair substitution in a non-coding region
    C. A protein translated incorrectly from DNA
    D. Ten-base-pair duplication

END OF CONTENT