Biology Chapter on Evolution and Speciation

Exam Information

• Exam date: Feb. 5th
• Time: 8:30-9:45
• Location: WWH, room 135
• Format: In-person, on paper

Darwinian Evolutionary Theory

• Before Darwin's theory, the first scientific explanation for evolution was proposed by Jean Baptiste de Lamarck (1809).
• Lamarckism described evolution as the inheritance of acquired characteristics.
• Darwin supported his theory with key pieces of evidence, including perpetual change (the world's ever-changing nature with continuity from past to present), fossil records (revealing dramatic environmental changes), and evolutionary trends (directional changes in features and diversity, demonstrating perpetual change - species arising and extinction).

Darwinian Evolutionary Theory - The Evidence (cont)

• Common Descent: Life's history is depicted as a branching tree (phylogeny). All living things descended from a common ancestor. The last universal common ancestor (LUCA) existed over 4 billion years ago, resembling living bacteria.
• Homology and Phylogenetic Reconstruction: show evidence for common descent, with characteristics inherited and modified from common ancestors.

Speciation

• Speciation occurs due to a lack of gene flow (reproductive barriers) between populations
• Allopatric Speciation: Occurs when geographically isolated populations evolve independently and adapt to their environments:
  • Dispersal & colonization: Individuals disperse from a population to colonize a new habitat.
  • Vicariance: Some chance event physically isolates populations into subgroups.
• Sympatric Speciation: Occurs among populations in the same geographical area. Individuals become specialized to occupy different components of the environment.

Forces of Evolutionary Change

• The driving force behind evolutionary change is a change in allele frequencies within a population. This can result from any combination of four processes:
  • Mutation: Continuously introduces new alleles.
  • Genetic Drift: Random change in allele frequencies
  • Gene flow/migration: Individuals migrate and breed with other populations.
  • Natural selection: increases allele frequency for reproductive success

Mutation

• Creates new alleles, not just new combinations. This can occur through point mutations, lateral gene transfer, duplication, or divergence.

Genetic Drift

• Chance changes in allele frequencies in a population.
• Randomly causes allele frequencies to drift up or down over time.
• Especially prevalent in small populations.

Gene Flow

• Movement of alleles between populations.
• Occurs when individuals leave one population and breed in another.
• Equalizes allele frequencies between populations

Natural Selection

• Can change both allelic and genotypic frequencies in a population.
• Heritable variation leads to differential survival and reproduction. Increases the frequency of alleles that contribute to reproductive success in the environment.

Reproduction

• Two types:
  • Asexual reproduction: Creation of new genetically identical individuals.
    • Examples: Binary fission, budding, fragmentation
  • Sexual reproduction: Promotes genetic diversity, enhancing survival of the lineage.
    • The fusion of gametes from genetically different individuals, creating offspring with a unique genotype.

Gametogenesis

• The production of mature gametes, including spermatogenesis and oogenesis

Spermatogenesis

• Occurs in the testes.
• Germ cells develop and produce male gametes (sperm) with Sertoli cells.

Oogenesis

• Occurs in the ovaries.
• Oogonia increase in number via mitosis.
• Primary oocytes arise and undergo meiosis I. The first polar body is created and the secondary oocyte awaits fertilization. Meiosis II is completed only when the secondary oocyte is penetrated by a spermatozoon

Reproductive Patterns

• Oviparous: Eggs laid outside body
• Ovoviviparous: Fertilized eggs remain in oviduct, embryos develop within eggs
• Viviparous: Fertilized eggs develop in oviduct, embryos gain nourishment directly from the mother

Developmental Studies

• Preformation vs. Epigenesis: Preformation hypothesizes that young organisms are pre-formed in the egg or sperm, while epigenesis posits that a fertilized egg contains building material that is assembled during development.
• Descriptions of the progressive changes in the development of an organism to maturity, emphasizing the developmental stages, including cleavage, blastula, gastrulation, and organogenesis.

Early Development

• Cleavage: Embryonic cell division.
• Blastula: Hollow ball of cells
• Gastrulation: Transformation from blastula to a multi-layered embryo.

Formation of Mesoderm Germ Layer

• Diploblastic: Two germ layers (ectoderm and endoderm)
• Triploblastic: Three germ layers (ectoderm, endoderm, and mesoderm)

Further Development

• Important characteristics and events of further development, including the development of the coelom, and the origin of the mouth (or anal region) in protostomes and deuterostomes respectively.

Amniotes and the Amniotic Egg

• Amniotes (reptiles, birds, and mammals) develop within a fluid-filled, membranous sac, the amnion. The amnion provides an aqueous environment protecting developing embryos from mechanical shock.

Development of Systems and Organs

• Gastrulation: Three germ layers are formed
• Differentiation: Cells become committed to specific directions for differentiation into organs and tissues.

Hierarchical Organization of Animal Complexity

• Protoplasmic: Unicellular organisms
• Cellular: Cell aggregation
• Cell-tissue: Cells form specific patterns or layers.
• Tissue-organ: Tissues aggregate to form organs.
• Organ-system: Organs work together to perform functions.

Animal Body Plans

• Differences related to organization, symmetry, and body cavities

Animal Symmetry

• Spherical Symmetry
• Radial Symmetry
• Bilateral Symmetry

Cellular Components: Tissues

• Tissues are groups of similar cells that work together to perform a common function.
• Histology is the study of tissues.
• Four types of tissues are: epithelial, connective, muscle, and nervous

Complexity and Body Size

• As body size increases, body volume increases more rapidly than surface area.
• Small animals tend to rely on diffusion for gas exchange, while larger animals have circulatory systems for transport.