Hybrid zones: zones of interbreeding between differentiated populations • 1. Hybrid zone narrow – 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 – 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.
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Hybrid zones: zones of interbreeding between differentiated populations
• 1. Hybrid zone narrow– 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– 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• 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-centralAZ
Primary contactPopulations divergewhile in contact
Aspidoscelis tigris
Release of F2 variationMimulus lewisii Mimulus cardinalis
Greya (moth genus): mtDNA data
Interpretations different with different species concepts
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