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14 Cards in this Set

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  • Back
what is speciation synonymous with under the biological species concept
reproductive isolation
What are 4 general models of speciation (defined by geography)?
1) allopatric (geographically isolated)
2) peripatric (small founding population enters isolated niche)
3) Parapatric speciation (new niche found adjacent to original one)
4) sympatric speciation (speciation occurs without physical separation)
What are the general 3 steps to speciation?
1) Initial barrier to gene exchange (intrinsic biological barrier or extrinsic physical barrier)
2) Divergence of lineages due to mutation, genetic drift, and/or selection
3) Completion of differentiation through to reproductive incompatability.
T or F. In all cases it is the reduction in gene flow among populations coupled with selection for local adaptation that is important
T. Reduce gene flow among populations and they are free to diverge from one another. add selective pressures and divergence may take place at high rates...diverge enough = new species
What are the 2 pathways of allopatric speciation?
1. vicariance- splitting of a population's former range onto 2 or more isolated patches (discourages/prevents geneflow b/w the 2 or more pops.)

2. founder events/dispersal--establishment of a new population, usually b y a small number of individuals.
Why does peripatric speciation (speciation among peripheral isolates) often involve small populations?
1. greater drift
2 the environment at the periphery of a species' range is often extreme relative to the normal environment of the organism (leading to potentially strong and divergent natural selection)
Define parapatric speciation again.
speciation in which the new species forms from a population contiguous (in close proximity) with the ancestral species' range.

define secondary contact.
when populations that were once isolated later came back into geographic sympatry.
What has a strong influence on what happens if the populations in allopatry come into secondary contact?
the degree of reproductive isolation that has arisen during the period of allopatry
Does allopatry always lead to speciation?
If allopatric distributions are present for long enough (thus, no gene flow among populations) speciation will likely occur...but if secondary contact occurs before reproductive isolation is complete, hybrid formation can result.
What are 3 possible outcomes of secondary contact and subsequent hybrid formation?
1)Hybrid offspring that are produced have reduced fitness relative to parentals due to reinforcement (produces complete reproductive isolation)
2)If hybrids occupy habitats that are different from those occupied by either parental population, hybrid could have higher fitness than both (this would create a new species)
3)No measurable difference found between the fitness of hybrid and parentals (hybrid zone = region where interbreeding b/w diverged populations occurs and hybrid offspring are frequent).
Define reinforcement.
selection for pre-zygotic isolating mechanisms due to pre-existing post-zygotic isolating mechanisms (hybrids only can mate with hybrids and originals with originals).--this process of positive assortive mating will tend to reinforce the speciation process started in allopatry
Reinforcement is an example of _________ selection for reproductive isolation
What are 3 potential mechanisms of sympatric speciation?
1) polyploidy (having more than 2 sets of haploid chromosomes)
2) Microhabitat segregation
3) strong selection and assortive mating