Speciation Flashcards
Define speciation.
The process by which one species becomes two species.
Define the morphological species concept.
Species are groups of individuals that share morphological characteristics in common.
Describe the biological species concept.
Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other groups
Who developed the biological species concept?
Theodosious Dobzhansky & Ernst Mayr
What are the three types of reproductive isolation?
Premating
Post-mating, pre-zygotic
Post-zyogtic
What is meant by premating as a type of reproductive isolation?
Different breeding/flowering times;
Incompatible sex organs
Prevents copulation
What is post-mating, pre-zygotic reproductive isolation?
Mating but not fertilization
What is post-zygotic reproductive isolation?
Offspring die or are infertile.
Describe the phylogenetic species concept.
A cluster of organisms that form a monophyletic clade.
What are the two steps to determining a species using the phylogenetic species concept?
o Estimating phylogeny
o Determining “groups”
Describe the pros of the morphological species concept (3).
- Easy, anyone can do it
- Doesn’t require expensive genetics
- Objective criteria
Describe the cons of the morphological species concept (4).
- Inaccurate, in part because what traits do you measure?
- Variation within species
- Cryptic species
- Convergent evolution
Describe the pros of the biological species concept (3).
- Objective definition
- Experimentally testable
- Based on the biology of organisms
Describe the cons of the biological species concept (3).
- Not always practical or ethical
- Infertility is not absolute
- Doesn’t work with everything (e.g., asexual species like bacteria)
Describe the pros of the phylogenetic species concept (3).
- Applicable to any group of organisms
- Reflects evolutionary history
- Objective
Describe the cons of the phylogenetic species concept (5).
- Expensive and time consuming
- Doesn’t necessarily reflect biology of species and mating
- Genes vary in rates of evolution
- Which gene?
- Might not be able to recognize different species
What are the three general types of speciation?
Allopatric
Parapatric
Sympatric
Describe allopatric speciation.
o Occurs when a single population of the same species is geographically separated into two or more populations by a geographical barrier
o Through time the separated populations diverge into separate species
What two mechanisms lead to the divergence of species in allopatric speciation?
Genetic drift
Natural selection
What are the two types of allopatric speciation?
Vicariance
Dispersal
Describe vicariance allopatric speciation.
Occurs when a single population of the same species is split into two by a new geographical barrier and through time the separated populations diverge into separate species
What are the mechanisms for vicariance?
Randomly mating population
Separated by a barrier – NO GENE FLOW
Divergence in isolation: Natural selection and genetic drift
Give examples of vicariance speciation discussed in class (2).
Chimps -> bonobos via Congo River
Abert squirrel -> Kaibab squirrel via Grand Canyon
What is believed to be the most important mechanism of speciation?
Dispersal (allopatric speciation)
Describe the dispersal form of allopatric speciation.
o Occurs when populations of the same species are geographically separated from each other because some individuals disperse away from the parent population
Describe the mechanism of allopatric speciation via dispersal.
Randomly mating population
Some individuals migrate away – NO GENE FLOW
Divergence in isolation: Natural selection and genetic drift
Give an example of allopatric speciation via dispersal discussed in class.
Darwin’s finches
Describe parapatric speciation.
o Occurs when a single population diverges into two species at its geographic extremes without a physical barrier
Describe sympatric speciation.
Occurs when a single population of one species splits into two species without any geographical barrier or separation
Describe the mechanism of sympatric speciation.
Randomly mating population
Strong potential for GENE FLOW
Populations diverge to be reproductively isolated
Give an example of sympatric speciation discussed in class.
Apple maggot fly (Hawthornes and apples, different development time)
What did Coyne and Orr 2004 establish about sympatric speciation? (4)
Largely overlapping geographic ranges
Speciation must be complete
Must be sister species
“…history of the groups must make the existence of an allopatric phase very unlikely”
Why is sympatric speciation likely to be rare?
The conditions for sympatric speciation are restrictive
Within sexual populations, when is sympatric speciation only likely? (2)
When there is strong divergent selection for a population to adapt to two resources, AND
When there is simultaneous selection for positive assortative mating
Explain why some species have more lineages than others and provide an example.
Number of species is a function of diversification rate and age of lineage
Some species diversify very quickly over time (e.g., birds) and thus have more lineages
How is diversification rate calculated?
Diversification rate = speciation rate – extinction rate
Provide the three explanations for why some geographic regions have more species than others.
- High rates of speciation
- Low rates of extinctions
- The area is older, and has accumulated more species through time
