Lecture 12 Study Notes on Speciation, Taxonomy, and Phylogeny

Evolution: Change in allele frequencies over time.
Modern Synthesis: Integration of population genetics with Darwinian evolution.
Four Forces of Evolution:
- Mutation: Change in DNA sequence introducing novel alleles, which can be neutral, disadvantageous, or advantageous. It increases variation within populations.
- Natural Selection: Differential reproductive success based on heritable traits, leading to types such as directional, stabilizing, or disruptive selection. It reduces variation within populations.
- Gene Flow: Migration of genes between populations increases genetic variation within populations while decreasing it between them.
- Genetic Drift: Random changes in allele frequencies, particularly influential in small populations (e.g., founder effect and bottlenecks).

This concept proves evolution is occurring as it describes a population not undergoing evolutionary forces—only these populations remain in equilibrium.
Natural Selection: The only non-random force leading to adaptations, which are developed in incremental steps, and each must provide some advantage despite inherent costs.
Disequilibrium can occur when rapid environmental changes outpace evolutionary adaptation.
Balanced Polymorphism: Maintains multiple alleles due to heterozygote advantage (e.g., carriers of a single sickle cell allele are protected from Malaria).
Extended Evolutionary Synthesis incorporates elements of developmental biology (evo-devo) and non-genetic inheritance to better understand biological diversity.

Chemical Level: Atoms, atomic bonds, and molecules.
Cellular Level: Molecules form specific cell types and organelles.
Tissue Level: Specific cells joining together.
Organ Level: Tissues combine to form organs.
Organ System Level: Multiple organs working together (e.g., kidney + bladder).
Organism Level: All organ systems function together in an individual.
Population Level: Conspecific individuals interacting (competition, cooperation).
Community Level: All interacting plant and animal species within an ecosystem.

Biology is fluid rather than discrete; flexibility and ongoing classification changes reflect more accurate physiological and phylogenetic relationships.

Concept by Alfred Russell Wallace: "Every species has come into existence, coincident in both space and time, with a pre-existing, closely allied species."
Species emerge through gradual accumulation of differences leading to reproductive isolation.

Defined by John Ray: “Species are groups of reproducing organisms.”
Primary criteria: A and B can produce offspring, thus belong to the same species.
Problems include:
- Non-testable for allopatric (spatially separated)
- Non-testable for allochronic (temporally separated)
- Non-testable in the fossil record
- Non-testable with asexual organisms.

Defined as: “Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.”
Main features:
- Uses potential interbreeding for flexibility in defining species.
- Eliminates zoo hybrids.
- Focus on reproductive isolation without genetic specification issues.

Recognition Species Concept: A species is an inclusive population of individual bi-parental organisms sharing a common fertilization (Paterson, 1985).
Ecological Species Concept: “A species is a lineage which occupies an adaptive zone minimally different from any other lineage and evolves separately.” (Van Valen, 1976).
- Niche: How a population interacts with its environment (habitat/diet).
Evolutionary Species Concept: “A species is a lineage evolving separately from others with its own roles and tendencies.” (Simpson, 1961).
Phenetic Species Concept: “A species is the smallest or most homogeneous cluster that can be recognized as distinct from others.” (Sneath & Sokal, 1973).
- Base on observable similarities without reference to ancestry.

Allopatric Speciation: Populations separated by geographical barriers.
Sympatric Speciation: Speciation without geographic separation as new behaviors disrupt mating.
Parapatric Speciation: Reduced gene flow in parts of a population experiencing rapid habitat changes.

Geographical separation: Different evolutionary paths (e.g., finches on islands).
Temporal separation: Continued evolution despite spatial overlap.
Social separation: Different adaptations in the same ecological niche.

Common misconception: Speciation regarded as an instantaneous event rather than a gradual process.
Significant evidence affirms that speciation is an evolutionary process leading to variation over time rather than isolated occurrences.

Habitat Isolation: Separate habitats reduce encounters.
Temporal Isolation: Different breeding times prevent mating.
Behavioral Isolation: Unique courtship behaviors deter mating between species.
Mechanical Isolation: Physical differences prevent successful completion of mating.
Gametic Isolation: Incompatibilities at the gametic level prevent fertilization.

Reduced Hybrid Viability: Hybrids do not develop successfully or are frail.
Reduced Hybrid Fertility: Hybrid offspring, like mules, may be sterile.
Hybrid Breakdown: Successful hybrids produce feeble progeny in subsequent generations.

Definition: Diversification of a founding species into multiple species filling various ecological niches.
Often occurs post mass extinction or geographical changes.

Hierarchical classification system reflecting evolutionary relationships:
- Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.
Taxonomy changes as biologists refine classifications based on phylogenetic relationships.
Binomial nomenclature is used for species naming, italicized (e.g., Homo sapiens).

Understanding the interconnectedness of life on Earth through speciation, classification, and evolutionary principles is crucial for grasping biological diversity and the processes driving these changes over time.