Reproductive Isolation and Speciation

Reproductive Isolation

• Prezygotic Isolation: Prevents mating between species. This can be behavioral, physical/biochemical incompatibility of reproductive processes, or temporal isolation (differences in breeding times or habitats).

• Postzygotic Isolation: Occurs after mating. This results from genetic incompatibility leading to a sterile or inviable hybrid offspring.

Concepts

• Morphological refers to physical appearance.
• Biological describes the ability of organisms to produce viable, fertile offspring.
• Evolutionary focuses on genetic differences.
• Ecological highlights distinct niches/habitats and how fossils help to identify these.

Allopatric Speciation

• Geographic Isolation: A physical barrier splits a population into subgroups, leading to isolation.

• Vicariance: A natural event, like a geological change, separates a population.

• Dispersal: Some members of a population migrate and establish a new, isolated population. Genetic drift plays a significant role in this situation since gene pools change more rapidly in small populations due to the impact of random chance.

• Gene pool: All the alleles present in individuals within a population. Mutations are a key source of variation, which can affect alleles.

Evolution

• Environment: Environments influence whether alleles are harmful, advantageous, or neutral.

• Mutations: Neutral mutations occur in non-reproductive cells (somatic cells).

• Evolution: Evolution represents a change in allele frequencies within a population over time. This can happen through adaptive (natural selection) or non-adaptive evolution (mutations, migration, genetic drift).

• Genetic drift: Random fluctuations in allele frequencies, especially significant in small populations. Bottleneck effects occur after disasters (natural or human-caused), and founder effects result from small groups establishing new populations.

• Adaptations: Favorable traits enhance survival and reproductive success. Evolution leads to increased fitness due to surviving and reproducing more effectively in a given environment.

• Fitness: Fitness changes due to environmental shifts.

• Fixed population: Populations where a single allele of a gene constitutes the entire population. Genetic variation may occur via further mutations.

• Natural selection: Stabilizing selection favors intermediate phenotypes. Directional selection favors one extreme phenotype. Artificial selection involves human choice of individuals for reproduction. Sexual selection enhances reproductive success based on attractiveness and mate selection.

Speciation

• Gene flow: If gene flow between populations ceases, allele frequencies in isolated locations can diverge and result in speciation.

• Sympatric Speciation: Speciation that occurs in the same geographic area; usually occurs via disruptive selection where extreme phenotypes are favored.

Taxonomy and Phylogenetics

• Taxonomy: Classifies organisms into hierarchical groups based on shared traits.
• Phylogenetics: Studies evolutionary relationships based on molecular data.
• Monophyletic groups: Include the common ancestor and all its descendants. Homologous traits are shared derived characters.
• Paraphyletic groups: Include a common ancestor and some but not all of its descendants.
• Polyphyletic groups: Do not include the common ancestor and do not accurately reflect evolutionary history. Analogous traits are not due to common ancestry.

Metabolism

• Metabolism: Chemical reactions in cells that break down nutrients for energy and eliminate waste.
• Energy sources: Phototrophs use the sun and chemotrophs use organic compounds.
• Prokaryotes: Diverse in metabolic strategies; can be autotrophs (CO2 source) or heterotrophs (organic compound source). Rapid reproduction, small genomes, and horizontal gene transfer contribute to their high genetic and metabolic diversity.
• Autotrophs: Obtain carbon from CO2 for building blocks.
• Heterotrophs: Obtain carbon from organic compounds (e.g., glucose).

Prokaryotes vs. Eukaryotes

• Prokaryotes: Bacteria and archaea; smaller and simpler structure; lack membrane-bound organelles; have simpler DNA structure.
• Eukaryotes: Larger and more complex; have membrane-bound organelles (e.g., nucleus, mitochondria, chloroplasts). Their larger genomes with more linear chromosomes and histone proteins contributes to genetic complexity. Sexual reproduction increases genetic variation in eukaryotes.

Symbiosis

• Endosymbiosis: One species lives inside another, as in mitochondria and chloroplasts.

Photosynthesis

• Photosynthesis: Converts solar energy into chemical energy (ATP and NADPH), followed by the synthesis of carbohydrates using CO2. More ATP supports multicellularity and complexity

Multicellularity

• Multicellular organisms: More efficient due to complexity and specialized cells. Integrated systems (like nervous systems) enhance responsiveness. Cell communication is essential for collaboration. Gas exchange, transport, and circulation are crucial for efficiency.

Animal Systems

• Circulatory systems: Open systems allow fluid to bathe tissues (low pressure, low efficiency). Closed systems (high pressure, high efficiency) regulate blood flow.

Animal Diversity

• Symmetry: Radial symmetry (can be divided into multiple mirrored halves). Bilateral symmetry (division into two mirrored halves).
• Germ layers: Formation of an embryo in the development of tissues and organs. Protostomes and Deuterostomes differ when it comes to the mouth/anus development.
• Chordate traits: Structures like myotomes, post-anal tails, pharyngeal slits, neural tubes, and notochords are indicative of these organisms.

Vertebrate Adaptations

• Invertebrates adaptations are focused primarily on exoskeletons which protect them from desiccation.
• Vertebrates adaptations focuses on their skin, scales, and/or feathers.
• Amphibians have external fertilization.
• Reptiles have internal fertilization and amniotic eggs (shelled).

Plant Adaptations

• Vascular plants have xylem and phloem.
• Seed plants produce seeds.
• Flowers enhance pollination and attract pollinators (coevolution with animals).

Plant Reproduction

• Alternation of generations: Plants alternate between haploid (gametophyte) and diploid (sporophyte) stages. Fertilization and dispersal are crucial for reproduction.

• Seed dispersal: Seeds protect and nourish the embryo. Pollen transfers sperm. Flowers attract animals for pollination. Fruits assist with dispersal.