Key Biological Concepts and Evolutionary Principles

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

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.

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.

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).

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.

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 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.

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.

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.

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.

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.

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.

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.

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