Speciation Flashcards
(24 cards)
Define species
A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. They do not breed successfully with other populations.
What is speciation?
Speciation is the evolutionary process by which new biological species arise.
What is microevolution?
Changes in allele frequencies within a population over successive generations.
What is macroevolution?
Evolutionary change above the species level.
What holds a population together, so that its members resemble each other more than they do other species?
Gene flow
What is reproductive isolation?
The existence of biological factors (barriers) that impede 2 species from producing viable, fertile offspring.
How can reproductive isolation be classified?
By whether factors act before (prezygotic) or after fertilisation (postzygotic)
What are the 5 prezygotic barriers?
- Habitat isolation
- Temporal isolation
- Behavioral isolation
- Mechanical isolation
- Gamete isolation
What are the 3 postzygotic barriers?
- Reduced hybrid viability
- Reduced hybrid fertility
- Hybrid breakdown
What is habitat isolation?
Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers.
What is temporal isolation?
Species that breed at different times of the day, different seasons, or different years cannot mix their gametes.
What is behavioral isolation?
Courtship rituals and other behaviours unique to a species are effective barriers.
What is mechanical isolation?
Morphological differences can prevent successful mating.
What is gamete isolation?
Sperm of one species may not be able to fertilise eggs of another species.
What is reduced hybrid viability?
Genes of the different parent species may interact and impair the hybrid’s development.
What is reduced hybrid fertility?
Even if hybrids are vigorous, they may be sterile.
What is hybrid breakdown?
Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile.
What happens if species with incomplete reproductive barriers come into contact?
Formation of hybrid zones
What are the 3 possible outcomes when closely related species meet in a hybrid zone?
- Reinforcement - strengthening of reproductive barriers
- Fusion - weakening of reproductive barriers
- Stability - continued production of hybrid individuals
What is allopatric speciation?
Geographic isolation.
Process: Populations are physically separated by a barrier, preventing gene flow.
Outcome: Isolated populations diverge genetically due to different selection pressures and drift, eventually leading to reproductive isolation and new species.
What is sympatric speciation?
Speciation within the same geographic area.
Process: Reproductive isolation arises without physical separation, often due to polyploidy, habitat differentiation, or sexual selection.
Outcome: Genetically distinct groups emerge within the same location, eventually becoming reproductively isolated.
What is parapatric speciation?
Speciation in adjacent populations with limited gene flow.
Process: Occurs when populations are next to each other, and there is some, but reduced, gene flow. Strong selection across the boundary can lead to divergence.
Outcome: Reproductive isolation evolves despite some ongoing gene exchange, often resulting in a hybrid zone.
What is peripatric speciation?
A small, isolated population diverges from a larger one.
Process: A small group from a main population becomes isolated, often at the edge of the species’ range.
Outcome: Genetic drift and natural selection act on the small population, leading to rapid genetic changes and reproductive isolation.
What factors affecting gene flow can cause sympatric speciation?
- Polyploidy
- Sexual selection
- Habitat differentiation
