Biology Chapter 8: Sex and Evolution

Chapter 8: Sex and Evolution

• Chapter discusses sexual and asexual reproduction, costs and advantages, and mating systems.

Sexual Selection Based on Eye Span (Stalked-Eyed Flies)

• Sexual selection in stalked-eyed flies is based on eye span.

Terms

• Gametes: Eggs or sperm
• Zygote: Single-celled embryo
• Gonads: Sexual organs
• Meiosis: Cell division that forms gametes, producing haploid cells
• Haploid: One chromosome from the diploid pair
• Diploid: Two homologous chromosomes
• Sources of genetic variation after reproduction:
  • Independent assortment
  • Recombination (crossing over)

Asexual Reproduction

• Offspring are typically identical to the parent (clones if asexual)
• Common in plants (vegetative reproduction)
• Lack variation (clones)
• Parthenogenesis: Asexual reproduction through producing diploid eggs
• Observed in insects, fish, lizards, and turkeys.
• Selfing: Organisms with both male and female gametes that fertilize each other, common in plants

Costs of Sexual Reproduction

• Maintenance of gonads
• Mate attraction
• Two-fold cost of meiosis (only 1.5 of parent's genes passed on versus 100% in asexual reproduction)

Advantages of Sexual Reproduction

• Genetic variation: Offspring adapt to changing environments.
• Genetic variation allows organisms to cope with changes in biological environments.
• Red Queen Hypothesis: Organisms must constantly alter their genotypes to prevent being overcome by pathogens.

Hermaphrodism

• Male and female function in the same individual.
• Can be simultaneous or sequential
• In plants:
  • Monoecious: Male and female flower parts on the same plant.
  • Dioecious: Male and female flower parts on separate plants.
• Many plants prevent selfing through self-incompatibility (SI) genes.

Sex Determination

• XY sex determination:
  • Factors affecting ratios: competition between X and Y sperm; selective abortion.
  • Segregation of chromosomes practiced by many bird species; XY are females
• Temperature-dependent sex determination: Alligators, turtles, some lizards
• Socially dependent sex determination: Blue-headed wrasse are sequential hermaphrodites.

Alteration of California Sheephead Life History from Fishing Pressure

• Graph shows changes in the age distribution of California sheephead populations over time due to fishing pressure.
• The study observed changes in the age at which sheepheads reproduce, and sex roles.

Evolution of Sex Ratio

• Rare sex advantage leads to a 1:1 sex ratio.
• Frequency-dependent selection: Fitness of males is higher when rare (compared to females)

Local Mate Competition

• Favors production of daughters (Haplodiploidy)
• Fertilized egg = female
• Unfertilized egg = male

Mating Systems

• Promiscuity: Most common in animals.
• Polygamy: Long-term bonds with more than one member of opposite sex.
  • Polygny: One male, multiple females
  • Polyandry: One female, multiple males
• Monogamy: Pair bond during offspring raising; sometimes beyond. Common where both parents equally contribute to offspring care

Mating Systems – Bluegill

• Different mating strategies exist in bluegill, including parental and cuckold/sneaker strategies

The Polygyny Threshold Model

• Territory quality of mated males influences female choice.
• Quality of territory affects male reproductive success and female choice of mates.

Sexual Selection

• Selection for specific traits in one sex by the opposite sex.
• Leads to sexual dimorphism (differences in appearance)
• Secondary sexual characteristics arise in three ways: dissimilar sexual function, male combat, and mate choice.

Long-Tailed Widowbirds (demonstration of female choice)

• Shows that female preference for specific male traits (in this case, tail length) can drive sexual selection. Long tails resulted in greater mating success.

Explaining Sexual Selection

• Handicap principle: Showing strength by enduring handicap
• Parasite-mediated sexual selection: Presence of parasites can prevent elaborate plumage or other displays.

This chapter explores the concepts of sexual and asexual reproduction, highlighting their respective costs and advantages, as well as various mating systems. Special emphasis is placed on sexual selection in stalked-eyed flies and the roles of gametes, zygotes, and genetic variation. Gain insights into key terms and examples related to reproduction processes.