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.