The Origin of Species Flashcards
What is the source of biological diversity?
The origin of species
Natural selection
The gradual adaptation of a population to its environment
Mechanism
Microevolution - the change in the gene pool of a population from one generation to the next
Speciation
the process by which one species splits into two or more species - explains both diversity and unity of life
The biological species concept
Defines a species as a group of populations whose members have the potential to interbreed in nature and produce fertile offspring (offspring that themselves can reproduce). Thus, members of a biological species are united by being reproductively compatible, at least potentially
What tends to keep members of different species from physically mating with one another?
Reproductive isolation - prevents genetic exchange (gene flow) and maintains a boundary between species
Prezygotic barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Postzygotic barriers
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Habitat isolation
Lack of opportunities to encounter each other
Temporal isolation
Breeding at different times or seasons
Behavioral isolation
Different courtship rituals
Mechanical isolation
Physical incompatibility of reproductive parts
Gametic isolation
Molecular incompatibility of eggs and sperm or pollen and stigma
Reduced hybrid viability
Hybrid development or survival impaired by interaction of parental genes
Reduced hybrid fertility
Vigorous hybrids that cannot produce viable offspring
Hybrid breakdown
Viable and fertile hybrids with feeble or sterile offspring
What are some problems with the biological species concept?
- There is no way to determine whether organisms that are now known only through fossils were once able to interbreed
- Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually
The morphological species concept
classifies organisms based on observable physical traits and can be applied to asexual organisms and fossils. However, there is some subjectivity in deciding which traits to use. Molecular data sometimes conflicts with morphological data
The ecological species concept
Defined a species by its ecological niche and focuses on unique adaptations to particular roles in a biological community. Hinges on ‘ecological niche’ concept - no two species can occupy the same niche
In allopatric speciation, what leads to speciation ?
Geographic isolation - a key event in the origin of a new species is the separation of a population from other populations of the same species
Allopatric speciation
The initial block to gene flow may come from a geographic barrier that isolates a population. Emergence of mountains or land masses, tectonic plate movements, changes in water level. Individuals colonize a remote area and become geographically isolated from the parent population
Can reproductive barriers evolve as populations diverge?
Yes - geographic isolation is just a first step in speciation
When does allopatric speciation become even more likely?
If the population sizes are small
Peripatric speciation
When both genetic drift and natural selection increase likelihood of divergence
Can sympatric speciation take place without geographic isolation?
Yes it can
Sympatric speciation
Occurs when a new species arises within the same geographic area as its parent species
What three things may reduce gene flow between populations?
Polyploidy, habitat differentiation, or sexual selection
Polyploidy
An organisms cells have more than two complete sets of chromosomes
- Auto-polyploidy: within a species (by self-fertilization)
- Allopolyploidy: between two species (by hybridization)
Can the origin of most plant species be traced to polyploid speciation?
Yes, 80% of all living plant species are descendants of ancestors that formed by polyploid speciation
Sexual selection
A form of natural selection in which individuals with certain traits are more likely to obtain mates - results from differences in how males attract females or how females choose mates
Hybrid zones
Regions in which members of different species meet and mate to produce at least some hybrid offspring
Reinforcement
When hybrid offspring are less fit than part species, we might expect natural selection to strengthen, or reinforce, reproductive barriers, because members of one species that don’t mate with the other have greater reproductive success
- Increasing reproductive barriers between species when they overlap (that is, where the species are sympatric)
Fusion
So much gene flow may occur that the speciation process reverses, causing the two hybridizing species to fuse into one
Stability
Many hybrid zones are fairly stable and production of hybrids does allow for some gene flow but the species remain isolated
Ring species
Species with a geographic distribution that forms a ring and overlaps at the ends
Does speciation occur rapidly or slowly?
It can occur both, rapidly or slowly
Punctuated change
Model draws on the fossil record, where species change most as they arise from an ancestral species and then change relatively little for the rest of their existence
Gradual change
Species appear to evolve gradually over time
