week 4.2 lecture slides

Biological Anthropology

• Subject: Evolution of Sex

Anisogamy

• Definition: Different gamete phenotypes that are usually haploid.

• Typical Gametes: Ovum (large, non-mobile) and sperm (small, mobile).

  • Sperm: Selected for low production costs, mobility, dispersal, and diversity but has low survival.

  • Ovum: Selected for high survival, high resource investment, and protection.

  • Competing demands of these characteristics.

Anisogamy: Sperm and Ova

• Common form of anisogamy with distinct functions:

  • Ova: Large, provides nutrients and developmental support.

  • Sperm: Small, mainly for dispersal and fertilization.

  • Role distinction: One is expendable, while the other is protected.

Anisogamy without Gender

• Hermaphroditism: Organisms possessing both types of gametes.

  • Compromise in body structures for independent maximization of dispersal and investment.

  • Sacrifices are made to increase the likelihood of mate location in low-density scenarios.

Advantages of Segregating Gametes

• Inherently advantageous for separate genders when mate location is difficult or costly (e.g., sessile creatures like barnacles).

Hermaphroditism in Plants and Animals

• Many flowering plants are hermaphrodites, having both male and female organs.

• Examples in animals include worms, snails, slugs, and clams (few vertebrates).

• Some vertebrates can change sex midlife.

Complex Organisms and Mobility

• Hermaphroditism linked to limited mobility within complex organisms.

  • Doubling the chance of finding a mate but limits optimization of body for reproductive roles.

Aphids and Reproductive Strategies

• Capability of switching between sexual and asexual reproduction.

  • Asexual offspring are maternal clones, allowing rapid colonization of host plants.

Reproductive Patterns

• Body types and behaviors reflect convergence of selection pressures on reproductive adaptations.

• Typical male/female distinctions result from co-adapted reproductive strategies.

Evolution of Body Types

• Different body types evolved for exclusive reproductive functions.

• No biological essence separates male from female; behavioral roles link to reproductive types.

Seahorse Reproductive Dynamics

• Males are "impregnated" by females laying eggs in the male's pouch.

• Eggs hatch in the pouch, young emerge for independent survival but may return for safety.

Reproductive Strategies

• Reproductive adaptations in an organism are often referred to as a "strategy" due to evolutionary competition.

• Male and female strategies complement each other but reflect trade-offs in reproductive strategies.

Blue-Headed Wrasse Behavior

• Begin life as females, in schools defended by a larger male.

• If the male dies, larger females can compete and one will transform into a male.

Anemonefish (Clownfish) Reproductive Adaptations

• Begin life as males with dormant female gonads.

• Pairs with older females that defend an anemone site for young.

• Upon female's death, the male undergoes sex change to female.