Two species regularly come into contact and form hybrids that have higher fitness than either of the parental species. What are some likely consequences of regular hybridization between these species? Check all that apply.

Question

_____  evolution of a third species
_____  reinforcement of prezygotic isolating mechanisms
_____  extincton of one or both of the parental species.
_____  increased gene flow between the parental species
_____  complete reproductive isolation of the two original species


Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you already know about gene flow before speciation?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

__X__  evolution of a third species
_____  reinforcement of prezygotic isolating mechanisms
__X__  extincton of one or both of the parental species.
__X__  increased gene flow between the parental species
_____  complete reproductive isolation of the two original species


Clarify Question
· What is the key concept addressed by the question?
        o This question addresses gene flow before speciation.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
 
Gather Content
· What do you already know about gene flow before speciation?
        o Gene flow may counter speciation.
        o When incompletely isolated populations come together, gene flow immediately begins to occur between them. Surviving hybrids that reproduce with members of either population serve as a conduit of genetic exchange from one population to the other, and the two populations will tend to lose their genetic distinctiveness.
        o Thus, a race ensues: Can complete reproductive isolation evolve before gene flow erases the differences between the populations? The outcome depends on the initial conditions and the particular species involved.
        o When hybrids are LESS fit than the parents, selection would favor any alleles in the parental populations that prevented hybridization, because individuals that did not engage in hybridization would produce more successful offspring.
        o In other words, selection would improve prezygotic isolating mechanisms until the two populations were completely reproductively isolated. This is called reinforcement.
        o If hybrids are MORE fit than the parents, reinforcement is not likely to occur.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Reinforcement of prezygotic isolating mechanisms will only occur when hybrids are less fit.
        o In this case, hybrids are more fit. So, reinforcement is not likely to occur, and complete reproductive isolation and speciation are not likely to occur.
        o Instead, there will likely be increased gene flow between the parental species.
        o There may be evolution of a third species, or even extinction of one of both of the parental species, since they may be outcompeted by the hybrid.
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that reinforcement of reproductive isolation requires that the hybrids are less fit than the parents?