Sexual Selection: Part II

Sexual Selection: Part II

Graph Types in Data Visualization

  • Understand the various types of charts used to communicate data effectively:

    • Bar Chart: Useful for comparing different groups or categories.

    • Line Chart: Ideal for showing trends over time or continuous data.

    • Histogram: Represents the distribution of numerical data.

    • Box Plot: Displays the distribution of data based on a five-number summary.

    • Pie Chart: Shows the composition of categories within a whole.

    • Area Chart: Similar to a line chart but filled with color to show volume.

    • Stacked Bar Chart: Shows data as parts of a whole across different categories.

    • Scatter Plot: Displays values for two variables for a set of data.

    • Heatmap: Represents data values through color coding.

Outline of Case Studies

  • Female Choice for Exaggerated Traits:

    • Question: Are exaggerated traits truly "good indicators" of male genetic quality?

  • Male-Male Competition in Galapagos Marine Iguanas:

    • Question: How is variation in male traits maintained under intrasexual selection?

  • Leks:

    • Question: Does cooperation among males benefit the individual?

  • Note: The last point will be discussed only if time permits.

Types of Evolution

  • Recall the five types of evolution:

    • Mutations: Changes in the DNA sequence that can affect traits.

    • Gene Flow: Transfer of genetic material between populations.

    • Non-Random Mating: Mating that does not occur at random; it can affect allele frequencies in a population.

    • Genetic Drift: Random changes in allele frequencies that occur in a population over time.

    • Natural Selection: Process where organisms better adapted to their environment tend to survive and produce more offspring.

Non-Random Mating

  • What counts as non-random mating?:

    • Example Distribution:

    • Random Mating:

      • 50% Probability of Choosing Yellow

      • 50% Probability of Choosing Orange

    • Non-Random Mating:

      • 80% Probability of Choosing Yellow

      • 20% Probability of Choosing Orange

Assortative vs Non-Assortative Mating

  • Non-Random Mating Analysis:

    • Assortative Mating: Preference for similar genotypes or phenotypes, leading to increased genetic similarity within mating pairs.

    • Disassortative Mating: Preference for different genotypes or phenotypes, promoting genetic diversity within populations.

Female Preference for Exaggerated Traits: Case Study of American Redstarts

  • Definition: A trait is considered an "honest signal" if positively correlated with important fitness traits.

    • Examples of fitness traits:

    • Immune responses

    • Ability to capture food

    • Ability to evade predators

    • Resistance to viral, fungal, or bacterial infections

    • Resistance to parasites

Female Preference for Exaggerated Traits: Case Study of Yellowthroats

  • Data on Health Metrics Related to Male Mask Size:

    • Figure 1 shows various measures:

    • a) Cutaneous immune response

    • b) Humoral immunity measured as plasma immunoglobulin G (IgG) concentration

    • c) Hematocrit measurement

    • Graphs indicate correlation between male mask size and these health metrics.

Case Study: Marine Iguanas in the Galapagos Islands

  • Behavior Observations:

    • Iguanas dive into cold water to feed on algae, then warm themselves on sunny rocks.

    • Males engage in headbutting behavior to defend rock territories.

    • Females bask in the sun on rocks.

Predictions on Iguana Body Size

Group Discussion Questions:

  1. In which sex (female or male) will natural selection shape the distribution of body shape? Which sex will be shaped by sexual selection?

  2. Create two graphs to showcase the distribution of body size—one for females and another for males.

  3. Predict an alternative mating strategy that might develop in this context.

Repeat Discussion Points

  • These questions are reiterated multiple times for group analysis and interaction.

Lekking Behavior of Males

  • Questions Addressed:

  • If males are competing for mates, why do species have males that group together during mating season?

  • Example Species: Male Greater Sage Grouse (Centrocercus urophasianus)

  • Definition: Lekking behavior involves males congregating to form a temporary group, known as a "lek", where they display for females.

  • Purpose: Females assess available males collectively and select one or few to mate with.

Female Choice vs Male-Male Competition in Leks

  • Brainstorming Exercise:

    • Provide reasoning for claims that a lek is driven by either:

    1. Female choice

    2. Male-male competition

    • Students to evaluate which argument is stronger based on evidence.

Theoretical Framework of Lek Strategy

  • Hotspot Theory: Suggests that females may travel up to 100 miles to leks because males serve as the resource females seek. Grouping increases the mating prospects and probabilities for all involved males.

  • Hotshot Theory: Indicates that alpha males tend to be centrally located in leks, and that around 20% of males account for approximately 80% of successful matings.