Chapter 24: The Origin of Species

Flashcards covering the concepts of biological species, reproductive barriers, allopatric and sympatric speciation, and hybrid zones from Chapter 24.

Species

Latin for “kind” or “appearance”

The Biological Species Concept

Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; it cannot be applied to asexual organisms, fossils, or organisms with unknown reproduction.

Reproductive Isolation

The existence of biological factors that impede members of two species from producing viable, fertile offspring; it is a prerequisite for the formation of a species.

Prezygotic barriers

Barriers that impede mating between species or hinder the fertilization of ova if members of different species attempt to mate.

Geographical isolation

A prezygotic barrier where species are in different geographical locations which prevents interbreeding.

Ecological (habitat) isolation

A prezygotic barrier where two species use different habitats in the same area and might rarely encounter one another, such as land-based and aquatic Garter snakes.

Temporal isolation

A prezygotic barrier where two species breed at different times of the day, seasons, or year, preventing the mixing of gametes.

Behavioral isolation

A prezygotic barrier involving rituals to attract mates or unique behaviors that prevent interbreeding, such as the courtship dances of the blue-footed booby.

Mechanical isolation

A prezygotic barrier where physical barriers prevent interbreeding, such as snails with shells spiraling in opposite directions.

Gamete incompatibility isolation

A prezygotic barrier where gametes are chemically matched to prevent interbreeding, often involving specific proteins on eggs and sperm to prevent fusion.

Postzygotic barriers

Barriers that often prevent the hybrid zygote from developing into a viable, fertile adult.

Reduced hybrid viability

A postzygotic barrier where hybrid offspring are weak or lack survival skills, as seen in the Insatina salamander.

Reduced hybrid fertility

A postzygotic barrier where the hybrid is vigorous but might be sterile or have reduced fertility, such as a mule.

Hybrid breakdown

A postzygotic barrier where the initial hybrid is viable and fertile, but subsequent generations are weak and sterile due to acquired mutant recessive alleles.

Allopatric speciation

Meaning “Other country,” this occurs when gene flow is interrupted or reduced because a population is divided into two or more geographically isolated subpopulations.

Sympatric speciation

Meaning “Same Country,” this involves speciation that takes place in geographically overlapping populations.

Polyploidy

The presence of extra sets of chromosomes in cells due to accidents during meiosis, frequently causing sympatric speciation in many plant species.

Autopolyploidy

A condition where an individual has more than two chromosome sets, all derived from a single species.

Allopolyploidy

A condition where a species has multiple sets of chromosomes derived from different species.

Hybrid zones

Regions where two related populations that diverged after being geographically isolated make secondary contact and interbreed where their geographic ranges overlap.

Reinforcement

A outcome in hybrid zones where pre-zygotic reproductive barriers are strengthened, especially between sympatric species, limiting the formation of hybrids.

Fusion

An outcome in hybrid zones where gene flow reduces barriers between species due to a lack of reproductive barriers, potentially reversing the speciation process.

Stability

A condition where hybrid zones become stable, such as in the case of Bombina Toads.