Study Guide for Speciation, Taxonomy, and Phylogeny Lecture

Evolution Defined:
- Evolution is the change in allele frequencies over time.
Modern Synthesis:
- Integration of population genetics with Darwinian evolution.
Forces of Evolution:
- Mutation: Changes in DNA sequences that introduce novel alleles (neutral, disadvantageous, or advantageous).
- Increases variation within and between populations.
- Natural Selection: Differential reproductive success attributed to heritable traits.
- Can be directional, stabilizing, or disruptive.
- Reduces variation within populations.
- Gene Flow: The migration of genes between populations which increases within-population variation and decreases between-population variation.
- Genetic Drift: Random changes in allele frequencies, impacting smaller populations significantly (e.g., founder effect, bottlenecks).

Definition: Used to demonstrate that evolution is occurring. Equilibrium is observed only in populations not affected by evolutionary forces.
Key Mechanism of Natural Selection:
- The only non-random force of evolution.
- Leads to adaptations, which evolve incrementally, requiring each step to offer an advantage, but adaptation can have costs.
- Constraints exist due to pre-existing biological factors.
Disequilibrium: Occurs during rapid environmental changes; evolution needs time to catch up.
Balanced Polymorphism: Maintains multiple alleles (e.g., sickle cell allele offers malaria protection).
Extended Evolutionary Synthesis: Incorporates evo-devo (evolutionary developmental biology) and non-genetic inheritance into the understanding of life's diversity.

Fluidity of Biology: Nature is inherently more fluid than discrete classifications.
Taxonomy: The classification of living organisms aims to reduce biological complexity through systematic groupings.
Criteria for Grouping Organisms: Consideration of genotype, phenotype, ecology, behavior, geography, and phylogeny (evolutionary history).
Taxa Definition: A taxon refers to any grouping of organisms, such as Dinosaurs or Homo sapiens.

Initial Definition: Proposed by John Ray: "species are groups of reproducing organisms."
Refinement by Ernst Mayr: "Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups."
- This definition applies flexibility with respect to allopatric conspecifics and maintains a natural reproductive barrier.

Limitations:
- Not testable in allopatric organisms (species separated by geographical barriers).
- Not testable in allochronic organisms (species separated in time).
- Inapplicable to the fossil record and asexual organisms.

Recognition Species Concept: Taxonomy based on shared fertilization among bi-parental organisms.
Ecological Species Concept: A lineage evolving separately within an adaptive zone distinct from other lineages.
Evolutionary Species Concept: Defines species as lineages with unique evolutionary roles and tendencies.
Phenetic Species Concept: Based on observable characters, classifying organisms independently of their evolutionary history.

Definition: The process through which new species arise from existing species, rooted in gradual changes.
Mechanisms of Speciation:
- Allopatric: Physical barriers lead to reproductive isolation.
- Sympatric: Speciation occurring within the same geographic area due to behavioral differences.
- Parapatric: Reduced gene flow across distinct environmental gradients.
- Peripatric: Small groups isolated at the periphery of the population.

Allopatric Speciation: Example of the Pacific Ocean separating populations leading to distinct species (e.g., Anisotremus taeniatus and Anisotremus virginicus).
Sympatric Speciation: Occurs without geographical separation; disruptive behaviors lead to speciation (e.g., changes in mating behaviors).
Parapatric Speciation: Focusing on variations across habitats may lead to developing new species from an existing population.

Factors Encouraging Divergence:
- Geographical barriers, temporal separation, and social structure (e.g., dietary specialization).

Understanding Speciation: Misconceptions suggest speciation is a sudden event rather than a gradual process. Evidence of gradual change supports evolutionary theory.

Prezygotic Barriers: Mechanisms that impede mating or fertilization.
- Types: Habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation.
Postzygotic Barriers: Prevent hybrids from developing into viable adults.
- Includes reduced hybrid viability, reduced fertility, and hybrid breakdown.

Definition: The diversification of a single ancestor species into numerous species adapting to different environments and niches.
- Often observed following mass extinctions.

Cambrian Period:
- Surge of multicellular life (Cambrian Explosion); increase in major animal phyla; conditions included warmer temperatures and shallow seas.
Ordovician Period:
- Characterized by high sea levels; preliminary land plants and intense mass extinction towards end.

Key Features of Amniotes: Embryonic developmental features such as the presence of the amnion facilitate life on land.
Evolution of Synapsid to Mammal Transition: Features such as mammary glands, fur/hair, and inner ear bones highlight the transition from therapsids to mammals, evidenced by many transitional fossils.