Ecology Week 6, Lecture 10 - Reproduction

Ecology Week 6, Lecture 10 - Reproduction

• Reproduction is how organisms pass their genes to the next generation.
• Sexual reproduction involves the fusion of male and female gametes to form a zygote.
• Asexual reproduction involves the production of spores or reproductive bodies by a single individual, creating clones. Vegetative reproduction is a type of asexual reproduction involving growth.
• Parthenogenesis is a form of asexual reproduction where offspring develop from unfertilized eggs.
• Selfing is when pollen fertilizes its own ovules in plants.

Sexual Reproduction

• Sexual reproduction is costly. Reasons include: attracting and finding mates, courtship displays, secondary sexual characteristics, and reproductive systems.
• Cost of meiosis means parents only contribute half the genes compared to asexual reproduction thus halving fitness and contribution to next generation.
• The cost of mating is the energy (time, resources, etc.) used by a species to find, attract and mate with individuals of the opposite sex.
• Sexual reproduction has benefits. These include: purging mutations (can accumulate in generations of clones), genetic diversity in the face of biotic changes (environment).
• The Red Queen hypothesis proposes that reproduction provides advantages because of a constant evolutionary arms race against pathogens, where organisms must continually adapt to avoid extinction. Offspring are genetically different from parents, thus less susceptible to pathogens ("moving target").

Sexes

• Females produce a larger gamete (eggs), resulting in fewer gametes for a given allocation of resources. Females are often limited by the number of gametes that can be produced, available resources, and the number of offspring they can raise/care for. This impacts how many offspring are raised.
• Males produce smaller gametes (sperm), resulting in more gametes for a given allocation of resources. Males are usually limited by the number of eggs that can be fertilized (mating limitations).

Sexuality

• In animals:
  • Unisexual: organisms are either male or female.
  • Hermaphrodites: organisms have both male and female functions.
    • Simultaneous: both sexual functions occur at the same time (e.g., worms, snails).
    • Sequential: sexual function develops in a sequence (e.g., some fishes or mollusks).
• In plants:
  • Dioecious: different sexes on separate plants.
  • Monoecious: individual plants bear distinct male and female flowers.
  • Perfect: flowers with both male and female parts (hermaphrodites); common in plants.

Self-incompatibility

• Strategies used if most plants are perfect (or hermaphrodites), and prevent selfing. This includes:
  • Self-incompatibility
  • Sequential hermaphroditism
  • Heterostyly

Sexual Selection

• All mating systems involve mate selection.
• Females usually do the selection because males are often limited by mating (benefit when mating with multiple females) and females are limited by resources (benefit by mating with quality males).
• Females select mates based on resources (parental care) and good genes.

Sexual Dimorphism

• Sexual dimorphism is a common result of sexual selection.
• Phenotypic differences between the sexes.
• Causes include differences in reproductive function (larger females due to eggs), male-male competition (larger males with combat weapons), and mate choice (larger/showier males favored by females).

Mating Systems

• Promiscuity: many mates (no pair-bonds, no parental investment). Most common in animals and outcrossing plants.
• Polygyny: one male with a group of females (harem).
• Polyandry: one female with a group of males.
• Monogamy: a pair-bond between one male and one female long enough to raise offspring. More common in birds or mammals.
• Extra-pair copulations: occurs even in monogamous species, where individuals mate with others outside their established pair-bond. This is detected using DNA fingerprinting.

Secondary Sexual Characteristics in Males

• Why would females select for extreme traits that may be detrimental?
  • Handicap principle ("Good Genes"): A male's exaggerated features (e.g. peacock's tail) demonstrate survival despite the handicap. Surviving these handicaps demonstrates superior genotype.
  • Runaway Sexual Selection ("Sexy Sons"): The preference for an exaggerated trait may become more extreme over time due to selection for the genes associated with the trait in males("sexy"). This creates a positive feedback loop.

This quiz covers key concepts of reproduction in organisms, exploring both sexual and asexual methods. You'll learn about the processes involved, including gamete fusion, vegetative reproduction, and parthenogenesis. Assess your understanding of the costs associated with sexual reproduction and its implications for genetic contribution.