Flashcards in Evolution- Origin of Species Deck (22)
What is speciation?
The focal point of evolutionary biology and the source of biodiversity. It is the conceptual bridge between micro and macroevolution
What is the Biological Species Concept? Limitations?
A population or group of populations whose members have the potential to interbreed in nature to produce fertile offspring. It hinges on reproductive isolation.
The limitations are asexual reproduction, fossil species, and geographically separate populations
What is reproductive isolation?
Any biological factor that stops individuals of 2 species from producing viable, fertile offspring
What are the 2 types of reproductive barriers?
2. Post zygotic
What types of isolation do pre-zygotic barriers rely on?(5)
1. Habitat -species occupy different habitats
2. Temporal- species breed at different times
3. Behavioural- courtship rituals and other behaviours keep species apart
4. Mechanical- morphological differences prevent mating
5. Gametic- gametes unable to fuse
What do post zygotic barriers rely on?(3)
1. Reduced hybrid viability- genes of different parent species may not work together and impair hybrid's development
2. Reduced hybrid fertility- hybrids are sterile ex. mule
3. Hybrid breakdown- some first generation hybrids are viable and fertile but offspring of the next gen are feeble or sterile
What are the 3 other definitions of species?
1. Morphological species concept
2. Ecological species concept
3. Phylogenetic species concept
What is the morphological species concept?
What are the two problems with this concept?
-Defined by physical appearance
-Can work for asexual and sexual species
- Can be used to make distinctions between fossils
- Polymorphic and siblings species
- Cryptic species
What is the difference between the Ecological Species Concept and the Phylogenetic Species Concept?
Ecological- View species in terms of ecological niche
Phylogenetic- define species as a set of organisms with a unique genetic history. Provides a clear, objective answer
What are the 2 different modes of speciation?
1. Allopatric- other place
2. Sympatric- same place
How are small populations affected by allopatric speciation?
More likely to undergo rapid change due to drift and selection. They are at the fringe of species that are good candidates
What does the definition of barrier depend on in allopatric speciation?
The ability of a population to disperse
How do separate populations evolve in allopatric speciation?
Independently through mutation, natural selection, and genetic drift
What is sympatric speciation?
Speciation in geographically overlapping populations
What is the difference between autopolyploidy and allopolyploidy?
In autopolyploidy, chromosomal duplication turns a diploid plant into a tetraploid plant and they can't interbreed with parent species.
In allopolyploidy, the hybrid may be sterile but may be able to reproduce asexually for many generations
What are the 3 patterns within hybrid zones?
1. Can occur in a band where adjacent species meet
2. Often have reduced fitness compared with parent species
3. Their distribution can be complex if parent species are found in multiple habitats within the same region
What are the 3 possible outcomes when closely related species meet in a hybrid zone?
1. Strengthening of reproductive barriers(reinforcement)
2. Weakening or reproductive barriers(fusion)
3. Continued formation of hubris barriers (stability)
What happens during reinforcement?
Occurs when hybrids are less fit than parent species and overtime, the rates of hybridization decreases. Reproductive barriers should be stronger for sympatric species
What happens during fusion?
If hybrids are as fit as parents, there can be substantial gene flow between species and if the gene flow is great enough, parent species can fuse into single species
What happens during stability?
Extensive gene flow from outside the hybrid zone can overwhelm section for reproductive isolation inside zone. In cases where hybrids have increased fitness, local extensions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers
What is punctuated equilibrium?
Occurs in periods of stasis and it is interspersed with rapid change