Speciation and Macroevolution

Flashcards covering key concepts related to gene flow, speciation, hybrid zones, and different models and mechanisms of evolution like gradualism, punctuated equilibrium, and polyploidy.

Gene Flow

The force that holds populations together into one species; its interruption is a key factor in speciation.

Species (Biological Definition)

A group of populations whose members can interbreed in nature and produce viable, fertile offspring, but not with other such groups.

Macroevolution

The large-scale evolutionary changes that occur over long periods, leading to the formation of new species and higher taxonomic groups.

Speciation

The evolutionary process by which populations evolve to become distinct species, typically involving the interruption of gene flow.

Diane Dodd's Experiment

An elegant experiment using fruit flies where populations were divided and raised on different food sources (starch vs. maltose) for 40 generations, demonstrating a rapid decrease in gene flow due to evolving mate choice preferences.

Allopatric Speciation

A form of speciation that occurs when a physical barrier geographically isolates populations, blocking gene flow and leading to their divergence into separate species (e.g., shrimp on either side of the Isthmus of Panama).

Sympatric Speciation

A form of speciation that occurs when populations diverge into new species while inhabiting the same geographic area, without a physical barrier (e.g., hawthorn flies and apple flies).

Temporal Separation

A reproductive isolating mechanism where populations diverge due to differences in their breeding or reproductive timing during the year.

Habitat Preference

A reproductive isolating mechanism where populations diverge due to favoring different habitats or resources within the same geographic area.

Hybrid Zone

A geographical area where two different species meet, interbreed, and produce hybrid offspring.

Reinforcement

An outcome in a hybrid zone where hybrids are inviable or sterile, leading to strong selection against interbreeding and further strengthening the reproductive isolation of the parent species.

Fusion

An outcome in a hybrid zone where hybrids are highly viable and interbreed extensively with each other and the parent species, causing the two parent species to merge back into a single species.

Stability (Hybrid Zone)

An outcome in a hybrid zone where hybrids form consistently and may be viable, but their contribution to gene flow is insufficient to cause either reinforcement or fusion, leading to a stable but limited level of hybridization.

Phyletic Gradualism

The traditional evolutionary model, proposed by Darwin, suggesting that changes in species occur slowly and steadily over long periods through gradual accumulating adaptations (e.g., horse evolution).

Punctuated Equilibrium

An evolutionary model proposed by Stephen J. Gould, which suggests that species experience long periods of little to no evolutionary change (stasis), 'punctuated' by short, rapid bursts of speciation and phenotypic change (e.g., the diversification of animal phyla).

Stephen J. Gould

A prominent paleontologist and evolutionary biologist who, along with Niles Eldredge, developed the theory of punctuated equilibrium.

Polyploidy

A condition in an organism's cells where there are more than two complete sets of chromosomes, which can lead to rapid speciation, especially in plants.

Autopolyploidy

A form of rapid speciation where an individual organism doubles its own chromosome sets, resulting in a polyploid offspring that is reproductively isolated from the parent in a single generation.

Allopolyploidy

A form of rapid speciation that occurs through hybridization between two different species, followed by a doubling of chromosome sets in the hybrid offspring, leading to a new, reproductively isolated polyploid species.

Diploid

A cell or organism containing two complete sets of chromosomes (2n), one inherited from each parent.

Tetraploid

A cell or organism containing four complete sets of chromosomes (4n), often a result of chromosome doubling.

Triploid

A cell or organism containing three complete sets of chromosomes (3n), which often leads to sterility or abnormal development.

Reproductive Isolation

The existence of biological factors (barriers) that prevent two species from producing viable, fertile offspring, thereby maintaining species boundaries.