Evolution: Key Concepts

• The exam has been postponed and will consist of Q&A format questions
• Unit 2 focuses on evolution

Agents of Evolution

• Agents include mutation, migration (gene flow), genetic drift, and natural selection

Allopatric Speciation

• Speciation occurs due to geographic isolation, such as a river splitting a population

Biological Species Concept

• Species are defined by the potential to interbreed and produce viable offspring
• Limitations exist; it doesn't apply to asexual organisms or is difficult to apply to geographically separated populations

Biological Systems Hierarchy

• Organization of life ranges from molecules to organisms to populations, communities, and ecosystems

Cladogram vs. Phylogram vs Chronogram

• Cladogram represents hypothesized relationships based on shared derived traits
• Phylogram illustrates both relationships and the amount of evolutionary change (branch lengths)
• Chronogram indicates relationships and time (branch lengths = time)

Convergent Evolution

• Unrelated species develop similar traits due to similar selective pressures acting independently

Convergent vs. Divergent Evolution

• Convergent evolution involves unrelated species developing similar traits
• Divergent evolution involves related species developing different traits

Cryptic Species

• Species that are morphologically identical but genetically distinct
• Example; Astraptes fulgerator butterflies

Ecological Species Concept

• A species is a set of organisms exploiting a specific ecological niche

Endosymbiotic Theory

• Some organelles originated as free-living prokaryotes engulfed by a host cell
• Primary endosymbiosis; engulfment of prokaryotes such as chloroplasts from cyanobacteria
• Secondary endosymbiosis; engulfment of another eukaryote, such as Euglena's chloroplast

Evolution (Two-Step Process)

• Step 1; Variation arises in a population through mutation and recombination
• Step 2; Proportions of variants change across generations via selection, drift, migration, or mutation

Fixation of Alleles

• One allele becomes the only allele present in a population, potentially due to genetic drift

Gene Pool

• The complete set of alleles present in all individuals in a species

Genetic Drift

• Random changes in allele frequencies, particularly impactful in small populations
• Examples include bottlenecks and founder effects

Gene Flow/Migration

• Movement of alleles between populations, introducing genetic diversity and/or homogenizing populations

Homologous Structures

• Structures with shared ancestry but potentially different functions
• Example; tetrapod limbs

Heritable vs. Acquired Traits

• Heritable traits are genetic and passed to offspring
• Acquired traits develop during an organism's lifetime and aren't inherited

Irreducible Complexity

• Argument that complex structures cannot evolve gradually is refuted by mollusk eye diversity

Macroevolution

• Large-scale evolutionary changes, such as the origin of tetrapods or cycad radiation

Microevolution

• Changes in allele frequencies within populations, such as antibiotic resistance in bacteria

Molecular Clocks

• Genetic data estimates divergence times between species, calibrated with fossils

Monophyletic vs. Paraphyletic

• Monophyletic groups (clades) include an ancestor and all descendants
• Paraphyletic groups include an ancestor and some, but not all, descendants

Natural Selection Types

• Directional selection favors one extreme trait
• Stabilizing selection favors intermediate traits
• Disruptive selection favors both extremes

Phylogenetic Fuse

• A delay between clade origin and diversification
• Cycads originated in the Mesozoic but recently experienced diversity

Phylogenetic Tree Types

• Diagrams show branching patterns to represent evolutionary relationships

Pollinator Shifts

• Examples include changes in floral traits that attract specific pollinators
• spur length in Aquilegia leading to reproductive isolation

Pollination Syndromes

• Floral traits attract specific pollinators
• Example, red tubular flowers attract specific pollinators

Prezygotic Barriers

• Barriers prevent mating or fertilization
• Examples include habitat isolation, temporal isolation, and mechanical isolation

Primary vs. Secondary Endosymbiosis

• Primary endosymbiosis; eukaryote engulfs a prokaryote, such as archaeplastida (red/green algae)
• Secondary endosymbiosis; eukaryote engulfs another eukaryote, such as stramenopiles (diatoms) engulfing red algae

Reproductive Isolation

• Mechanisms include prezygotic (prevents mating/fertilization) and postzygotic (prevents hybrid viability/fertility) barriers

Sources of Genetic Variation

• Mutation (introduces new alleles) and recombination (shuffles alleles during meiosis)

Sympatric Speciation

• New species evolves from a single ancestral species while inhabiting the same geographic region

Theory of Endosymbiosis

• Chloroplasts/mitochondria have circular DNA like bacteria, reproduce via binary fission, and have double membranes

Transitional Fossil

• Fossils show intermediate traits between ancestral and derived groups, such as Tiktaalik
• Transitional fossils bridge gaps between major groups and support macroevolutionary patterns

MEGA Plate Experiment

• Demonstrates bacterial evolution under increasing antibiotic gradients and allele fixation

Reconstructing Phylogeny

• Uses molecular or morphological data and applies parsimony methods with software like Mesquite

Macroevolutionary Patterns

• Large-scale trends like the Cambrian explosion and mass extinctions
• Fossils are used to calibrate phylogenies

Endosymbiosis in Photosynthetic Lineages

• Primary endosymbiosis gave rise to chloroplasts
• Secondary endosymbiosis events are also important

Anolis Lizards

• Underwent adaptive radiation and diversified into distinct ecological niches in the Caribbean

Cycads

• Considered "living fossils" due to ancient origins and low morphological change

Mollusk Eyes

• Demonstrate a range from simple light-sensitive patches to complex camera eyes, reflecting gradual evolution

Aquilegia (Columbines)

• Spur length affects pollinator preference, leading to reproductive isolation

Bacterial Resistance

• Demonstrates natural selection, as bacteria with resistance mutations survive and spread in antibiotic-rich environments

Hypothesis vs. Theory

• Hypothesis is a testable prediction
• Theory is well-supported by evidence

Homologous vs. Analogous Structures

• Homologous structures share ancestry but may have different functions, such as tetrapod limbs
• Analogous structures have similar functions but independent origins, such as wings in bats and birds

Microevolution vs. Macroevolution

• Microevolution involves small-scale changes in gene frequencies within a population over short periods of time
• Macroevolution involves large-scale changes over long timespans, resulting in the formation of new species or higher taxa

Directional vs. Stabilizing vs. Disruptive Selection

• Directional selection; favors one extreme
• Stabilizing selection; favors intermediate
• Disruptive selection; favors both extremes

Prezygotic vs. Postzygotic Reproductive Isolation

• Prezygotic isolation; prevents mating or fertilization
• Postzygotic isolation; results in hybrid offspring that are either inviable or infertile

Parsimony Method vs. Maximum Likelihood Method

• Parsimony; minimizes the number of evolutionary changes
• Maximum likelihood; builds the tree that has the highest probability of producing the observed genetic data