Transcript Lecture 24 (4-4-11)

Hybrid zones: zones of interbreeding between differentiated
populations
• 1. Hybrid zone narrow
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A. hybrid zone recently formed.
B. fitness of hybrids may be lower than parental individuals.
If so, then reinforcement can take place.
Differences between parental populations are enhanced.
Final stages of speciation.
• 2. Hybrid zone broad
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A. Fitness of hybrids equal to parental species.
Parental populations converge phenotypically.
Differences decrease.
B. Fitness of hybrids greater than parental species.
Stable hybridization zone or speciation.
• A hybrid zone reflecting secondary contact
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Populations diverge in allopatry
Range shifts bring populations into sympatry
Pattern of variation
Low variation in F1s
High variation in F2s, F3s, etc.
Measure of variation (continuous characters)
– CV = coefficient of variation
– CV = (s/mean) x 100
Aspidoscelis tigris
Secondary contact
center
Aspidoscelis tigris
Clinal variation in
southern Arizona
Southwest AZ
South-central
AZ
Aspidoscelis tigris
Primary contact
Populations diverge
while in contact
Release of F2 variation
Mimulus lewisii
Mimulus cardinalis
Greya (moth genus): mtDNA data
Interpretations different with different species concepts