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A. tigris punctilinealis and A. tigris marmorata ORA. tigris and A. marmorata?
3. One species or two?
Fertilehybrids
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The hybridization zone: SW New Mexico
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Three concordantstep-clines
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Hybrid zones
• 1. Fitness of hybrids less than parental species.
• Hybrid zone narrow.
• Reinforcement.
• Differences between parental populations increase.
• 2. Fitness of hybrids equal to parental species.
• Hybrid zone broad.
• Parental populations converge;
• Differences between parental populations decrease.
• 3. Fitness of hybrids greater than parental species.
• Stable hybridization zone or speciation.– Red wolf?
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• Secondary contact
• 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
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Release of F2 variationMimulus lewisii Mimulus cardinalis
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Aspidoscelis tigris
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Secondary contact
center
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Primary contact
Aspidoscelis tigris
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Aspidoscelis velox (3n, parthenogenetic)
1. A. gularis stictogramma x A. inornata 2. F1 diploid parthenogenetric x A. inornata
Aspidoscelis uniparens (3n, parthenogenetic)
1. A. inornata x A. gularis stictogramma 2. F1 diploid parthenogenetic x A. inornata
Problem 4: Cryptic species
velox
uniparens
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• Barriers to interspecific hybridization
• Reproductive isolating mechanisms
• A. Prereproductive (favored by natural selection)
– 1. Ecological
• Temporal (phenological)
• Habitat segregation
– 2. Behavioral
– 3. Mechanical
• B. Postreproductive
– Gametic wastage
• Other species concepts
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• Phylogenetic Species Concept(s)
• Phylogenetic species: the smallest aggregation of individuals diagnosable by a unique combination of character states.
• Characters and character states• Organisms are grouped into species because of shared
derived character states inherited from a common ancestor• Ancestors and derived species form a branching pattern of
divergence• Ancestral populations do not (by definition) persist past a
speciation event.
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Greya (moth genus): mtDNA data
Interpretations different with different species concepts
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• The Evolutionary Species Concept– E. O. Wiley. 1978,1981, 2001.
• • A species is an entity composed of organisms
– maintaining its identity from other such entities through time and space
– and having its own independent evolutionary fate and historical tendencies.
• Operationalism absent• Use fixed diagnostic differences