Species and Speciation Flashcards
(34 cards)
Define biological species concept and give its limitations
Interbreeding organisms that produce fertile offspring and evolve independently of other populations.
Does not include asexually reproducing organisms, cannot be applied to fossils or geographically separated populations, incomplete knowledge of species that may interbreed successfully.
What are other species concepts and their limitations?
Phylogenetic - ancestral analysis - few complete phylogenies available, doesn’t address mechanism.
Morphological - differences in morphology - subjective criteria and interspecies variation often higher than intra
Ecological - based on environmental context - niche hard to characterize
What are the prezygotic isolating mechanisms and an example of each?
Potential mates don’t meet in space or time (seasonal/habitat)
Potential mates meet but don’t mate (ethological)
Mating attempted but no zygote formed (mechanical)
What are the postzygotic isolating mechanisms, how do they occur and what is an example of each?
Due to sufficient genetic divergence of isolated populations.
Gametic mortality
Zygote mortality
Hybrid inviability
Hybrid sterility
How do gene incompatibilities lead to genetic isolation?
Mutant alleles at different loci could be incompatible. If they become fixed, reproductive isolation occurs.
What are sympatric, allopatric and parapatric species?
Sympatric - occur in same geographical area.
Allopatric - occupy different geographic areas and don’t meet.
Parapatric - only meet along borders of their ranges.
What is anagenesis? Cladogenesis?
Anagenesis - one species gradually turns into the other
Cladogenesis - one species give rise to two or more species
What are the two sources of hybrid sterility, what are they and what are examples of each?
Chromosomal - improper pairing due to differing chromosome structure (gametes have incomplete complements of genes).
Genic - genetic composition too different
What is a hybrid zone?
Zone of interbreeding species
What would you predict if hybrid fitness is lower than either parent fitness?
- A very narrow hybrid zone
- Reinforcement
What would you predict if hybrid fitness is higher than either parent?
Can lead to extinction of the species with lower fitness
What is reinforcement?
Reinforcement occurs when natural selection favors the traits in two distinct populations over maladaptive hybridization
What is a cline?
Gradual change over a gradient
What is geographic variation?
When a trait varies in different geographic areas of the same species.
What is an ecotype? Give an example.
Gradient of variation of a short transect.
Example: High and low altitudes variants of a trait in a species that occupies both
What is character displacement? Give an example.
Character displacement is the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species’ distributions do not overlap.
Example: Three-spined stickleback, limnetic and benthic type and hybrids are selected against but intermediate form is present when there is only one species in a lake.
What are the three main types of variation within populations?
Morphological
Genetic
Behavioral
What are two modes of polymorphism in an evolving population?
Transitional - one allele replacing the other
Balanced - stable intermediate frequency
Is phenotypic variation necessary for genetic variation?
No, genetic variation can be latent.
How could you identify a variant gene locus in a protein?
By finding an invariant enzyme that corresponds to it.
What is linkage disequilibrium? How is it determined? How does it happen? What eliminates it? Why is it important?
Nonrandom association of alleles at different loci in a given population.
If the frequency of association is higher or lower than would be expected if the alleles were independent/randomly associated.
Natural selection - selective sweeps; random genetic drift, onset of populations interbreeding
Eliminated by recombination, which breaks down non-random genetic associations.
It causes alleles to deviate from expected frequencies, can slow evolutionary change, can also maintain specific allele combinations.
What is coadaptation?
Adaptive combination of alleles at various loci
What three steps are involved in speciation?
Genetic isolation, genetic divergence and then maintaining reproductive isolation.
Describe how allopatric speciation occurs. What are the two main types of allopatric speciation?
Describe how sympatric speciation occurs.
Describe how parapatric speciation occurs.
Allopatric - populations become geographically isolated so gene flow ceases. Genetic divergence through evolution leads to independently evolving populations. Examples: dispersal/colonization and vicariance. Organism example: Hawaiian Drosophila
Symaptric - divergent natural selection overwhelms gene flow. Mechanisms that reduce gene flow and allow this to occur are spatial, temporal and behavioral isolation, also polyploidy.
Parapatric - Reproductive isolation occurs with limited gene flow. Organism example: ring species CA salamanders
