Natural Resources Ecology - Reproductive Strategies

Life History Traits:
- Represent the schedule of an organism’s life.
- Shaped by trade-offs.
- Variability in the number of reproductive events among organisms.
- All organisms eventually experience senescence.
- Life histories are influenced by environmental conditions.

Reproductive Strategies:
- Reproduction can be categorized as sexual or asexual.
- Organisms can evolve as either separate sexes or hermaphrodites.
- Offspring sex ratios are typically balanced but can be modified through natural selection.
- Mating systems describe the mating patterns between males and females.
- Sexual selection favors traits that facilitate reproduction.

Definition: Produces genetically different offspring.
- Male gametes (sperms) fertilize female gametes (eggs) to form a zygote.
- Zygotes are diploid, containing a combination of chromosomes from both parents.

Dilemma: A population of asexual females can grow at twice the rate compared to sexually reproducing populations; however, most organisms reproduce sexually.
Costs:
- Evolution of costly sexual organs.
- Risky mating behaviors.
- Costs of meiosis, resulting in a 50% reduction in genetic contribution to offspring.
Benefits:
- Purging mutations from the gene pool.
- Increased genetic variation helps populations cope with environmental changes.
- Cooperative care of offspring from both parents.
- Coping mechanisms against parasites (co-evolutionary arms race).

Concept Summary:
- Proposed in a quote from Lewis Carroll’s "Through the Looking Glass" and further articulated by Leigh Van Valen in 1973.
- Suggests that continual evolution is necessary to maintain relative fitness in a co-evolving ecosystem.
Implication for Sexual Reproduction:
- Facilitates genetic recombination, helping hosts escape rapidly evolving parasites.
- Asexual reproduction increases susceptibility to infections due to lack of genetic diversity.
Arms Race:
- Hosts and parasites/predators engage in an evolutionary arms race to adapt defenses and overcome them, aiming to maintain fitness.

Example: P. antipodarum snails in shallow waters show higher rates of sexual reproduction compared to deeper waters.
Experiments suggest that trematode worms are more effective at infecting shallow water snails, demonstrating the evolutionary dynamics between parasites and hosts.
- Reference: Curtis M. Lively et al. (2011) study on nematodes and pathogenic bacteria supporting sexual selection.

Definition: Defines the quantity of mates each individual has and the nature of relationships.
- A female's reproductive success depends on egg production and mate quality; a male’s depends on the number of females fertilized.
Extra-pair Copulation: Occurs when a mate with a social bond breeds with others to enhance genetic variability among offspring.
Impact Example: Bluethroat chicks sired through extra-pair copulation show improved immune response.

Definition: A form of natural selection that influences reproductive success based on sex-specific traits.
**Primary vs. Secondary Sexual Characteristics:
- Primary:** Traits necessary for fertilization.
- Secondary: Traits that reflect differences in body size, color, ornaments, and courtship rituals.
Sexual Dimorphism: Differences in phenotypes between sexes of the same species (e.g., body size, courtship behaviors).
- Influences competitiveness in attaining mates.

Hypothesis Overview: Females preferentially choose mates that provide material benefits or contribute to fitness.
Example: Male long-tailed widowbirds attract females based on tail length, which has no direct material benefit but signals overall fitness.
Good Genes Hypothesis: Choosing mates based on superior genotypes to enhance offspring health.
Runaway Sexual Selection and Handicap Principle: Explains how certain traits proliferate through sexual selection until limited by genetic variation.
- Example: Infected rock doves with missing feathers were less attractive to females, demonstrating the cost of parasitism on mate selection.