Speciation Flashcards
If gene flow stops, what happens to isolated populations?
- Allele frequencies can diverge
- Populations begin to evolve independently
- Divergence may occur due to mutation, natural selection, and genetic drift
What is speciation?
When genetic divergence results in two or more distinct species stemming from an ancestral species
What is the Morphological Species Concept?
When a species shares more similar characteristics with each other because of shared evolutionary history
What is the Genetic Species Concept?
When species share more similar DNA because of shared evolutionary history
What is the Biological Species Concept?
A species contains groups of organisms that can interbreed and produce viable offspring and are reproductively isolated from other species
After splitting off from an ancestral population, each new population evolves in what ways?
Develop mutations independently
Each population has different selective environments
Members of the same species are linked by what?
Shared evolutionary history via the ability to exchange genetic information
What are the limitations to the Biological Species Concept?
Hybrids, extinct organisms, and asexually reproducing species
What are the limitations to the Morphological Species Concept?
Variation within species is tremendous
What are the limitations to the Genetic Species Concept?
Variation within species is tremendous
What is another definition for speciation?
The process by which populations attain reproductive isolation
What is reproductive isolation?
Biological barriers that impede members of different species from interbreeding and producing viable, fertile offspring
What are the 2 categories of biological barriers?
Pre-zygotic and post-zygotic barriers
What are pre-zygotic barriers?
Barriers that prevent mating or fertilization if mating does occur
What are post-zygotic barriers?
Barriers that prevent hybrid offspring of two species from developing into viable, fertile adults
What are the 5 pre-zygotic isolating mechanisms?
- Habitat (ecological or spatial) Isolation
- Temporal or Seasonal Isolation
- Behavioral Isolation
- Mechanical Incompatibility
- Gametic Isolation
What is Habitat Isolation?
When habitat preferences lower the probability of mating between individuals associated with different habitats
What is Temporal or Seasonal Isolation?
When species are prevented from interbreeding due to differences in the timing of mating or fertility, such as having different mating seasons
What is Behavioral Isolation?
When mating behavioral differences prevent mating
What are 2 examples of mating behavioral differences?
- Incorrect courtship displays
- Can’t recognize mating signals
What is Mechanical Incompatibility?
When morphological differences, often in genitals, prevent mating
What is Gametic Isolation?
When the sperm does not survive or physically cannot fuse with the egg
What are the 3 post-zygotic isolating mechanisms?
- Reduced hybrid viability
- Hybrid infertility
- Hybrid breakdown
What is Reduced Hybrid Viability?
The death of a zygote or organism
What is Hybrid Infertility?
When a hybrid lives, but is sterile
What is Hybrid Breakdown?
When the viability or fitness of a hybrid decreases with subsequent generations
What is Allopatric Speciation?
When reproduction is prevented by geographic isolation of a previously continuous population
What are the two ways allopatric speciation can occur?
Vicariance and dispersal
What is vicariance?
When a physical barrier splits a population into subgroups that are physically isolated from each other
What is dispersal?
When a population moves to a new habitat, colonizes it, and founds a new population
What is Biogeography?
The study of how species and populations are distributed geographically
What can Biogeography tell us?
How vicariance and dispersal events can occur
What can colonization (dispersal) events lead to?
Speciation
What is parapatric speciation?
Geographically continuous populations over extremely vast distances experience divergence
Different ends of a parapatric species have two characteristics:
- Functionally isolated from each other
- Experience distinct selective pressures
What is a ring species?
Continuous populations over large geographic areas form a ring where the populations rejoin
What is frequency-dependent selection?
When the fitness of a phenotype or genotype depends on the phenotype or genotype composition of the population
Populations or species that live in the same area and are close enough to interbreed are called what?
Sympatric
What is sympatric speciation?
When speciation occurs among populations in the same geographic area
What are the two events that initiate sympatric speciation?
- Internal events- chromosomal mutations
- External events- disruptive selection (different ecological niches or mate preferences)
What is polyploidy?
When cells have more than one pair of chromosomes
Polyploidy is a mutation important for what?
Speciation
Where is polyploidy most commonly seen?
In plants
What is autopolyploidy?
A mutation that doubles chromosome number when the chromosomes all come from the same species
What is allopolyploidy?
When parents of different species mate and an error in mitosis occurs, resulting in viable, nonsterile offspring
What is a niche?
Range of ecological resources that a species can use and the range of conditions it can tolerate
Sympatric species are not geographically isolated, how else can they be isolated?
Reproductively isolated due to adapting to different ecological niches via disruptive selection
What is a hybrid zone?
A geographic area where interbreeding between two populations occurs and hybrid offspring are more common
Depending on the hybrid offspring fitness and extent of breeding between parental species, hybrid zones can be (three answers):
- Narrow or wide
- Long or short lived
- Stable in one place or move over time
Describe how new species form through hybridization
Two species may interbreed and produce hybrid offspring that survive, reproduce, and posses a unique combination of traits adaptive to their particular environment, which may result in a new species
What are the 5 possible outcomes of secondary contact between species
- Fusion of the populations
- Reinforcement of divergence
- Hybrid zone formation
- Extinction of one population
- Formation of new species
Describe fusion of populations as an outcome of secondary contact between species
When the two populations freely interbreed
Typically happens when two populations of the same species come in contact with each other
Describe reinforcement of divergence as an outcome of secondary contact between species
Hybrid offspring have low fitness and natural selection favors the traits that prevent interbreeding between the populations
Describe hybrid zone formation as an outcome of secondary contact between species
Hybridization occurs in a well-defined geographic area
Describe extinction of one population as an outcome of secondary contact between species
If one population of species is a better competitor for shared resources, the poorer competitor may be driven to extinction
Describe formation of a new species as an outcome of secondary contact between species
If the combination of genes in hybrid offspring allows them to occupy distinct habitats or use novel resources, they may form a new species
What is negative frequency-dependent selection?
When a trait with a higher frequency is selected against (snails)
