Key Biological Concepts and Evolutionary Principles

Introduction to Sexual Selection

• Sexual selection is a fundamental concept in evolutionary biology.
• Aims to provide insights into mate attraction and reproductive success beyond mere survival.

Bateman's Principle

• Core idea focuses on the differential investment in reproduction between sexes.
  • Females: High energy investment in producing few but large eggs.
  • Males: Produce millions of tiny sperm, making success tied to access to females.
• Females' reproductive success is often limited by resource availability, while males face different pressures based on female access.

Reproductive Variance

• Defined as the variation in reproductive success among individuals.
• Typically higher in males; one male can fertilize many females, leading to significant reproductive differences.
• Higher variance = stronger sexual selection pressure.

Mechanisms of Sexual Selection

• Intrasexual Selection: Competition within the same sex, e.g., males fighting for dominance (e.g., deer antlers).
• Intersexual Selection: One sex, usually females, being choosy based on certain desirable traits, such as a peacock's tail.
• Selection occurs in multiple stages:
  • Pre-copulatory: Displays to attract mates (e.g., peacock tails).
  • Post-copulatory: Competition for fertilization (e.g., sperm competition).

Costs and Benefits of Traits

• Attractive traits like the peacock's tail can also be liabilities (e.g., predator visibility).
• Evolution seeks a balance between attracting mates and surviving predation.

Examples of Sexual Selection Strategies

• Side-Blotched Lizard: Demonstrates frequency-dependent selection where success depends on the commonality of strategies.

  • Aggressive males: Stronger but subject to competition.
  • Sneaky males: Mate while others fight.

• Barn Swallow Tail Manipulation Study: Longer tails led to higher mating success, supporting female choice.

• Bluegill Sunfish: Different mating strategies involving parental care vs. sneak fertilization show varied reproductive costs and benefits.

Female Competition

• Female investment often determines choosiness; e.g., in some species, females compete for males due to high parental investment.
• Example: Blooded sandpipers where males care for eggs and females compete.

Evolution of Virulence

• Not always straightforward; pathogens may evolve to be more harmful to aid in transmission:
  • Trade-off Hypothesis: Virulence balances host replication and transmission needs.
  • Directly transmitted pathogens tend to be less virulent while vector-borne pathogens can afford greater virulence.
• Examples include the West Nile virus and Marek's disease, demonstrating how virulence can change with host resistance.

Drug Resistance

• Rapid evolution of resistance in pathogens due to genetic variation and selective pressure from drug use:
  • Resistant individuals survive drug treatment, passing on genes.
• Antibiotic resistance in bacteria is exacerbated by overuse and high mutation rates.
• Horizontal gene transfer among bacteria spreads resistance rapidly.

Overall Impacts of Drug Resistance

• Implications for health, requiring judicious drug use and impact on beneficial microbiota.
• HIV: High mutation rates in reverse transcriptase lead to rapid resistance development, showcasing an ongoing battle in drug development.

Evolution of Symptoms as Defenses

• Some symptoms like fever and pain may serve defensive purposes rather than merely being malfunctions:
  • Fever: Could enhance immune function, despite being a sign of illness.
  • Anxiety: May signal the need for rest to prevent spreading illness.

Cooperation and Social Behavior

• Kin Selection: Strategy where individuals help relatives to pass on shared genes (e.g., slime molds).
• Game Theory: Explains cooperative behavior through models like the Hawk-Dove game which evaluates aggressive vs. passive strategies.

Reaction Norms and Phenotypic Plasticity

• Phenotypic Plasticity: Allows a single genotype to produce different phenotypes under varying environmental conditions (e.g., water flea morphology changes with predator presence).
• Reaction Norms: Graphical representation of how phenotypes vary with the environment; shows adaptability in evolutionary processes.

Conclusion and Final Thoughts

• Major themes involve the interconnectedness of evolutionary principles.
• Understanding these concepts can illuminate broader biological connections and aid in exam preparation.