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Lecture 25

BIOL 1001 Lecture Notes - Lecture 25: Hybrid Zone, Speciation, Species Complex


Department
Biology
Course Code
BIOL 1001
Professor
Alexander Mills
Lecture
25

Page:
of 1
Speciation: Re-contact after Isolation
Reinforcement = Wallace Eect
oNatural Selection increase Reproductive Isolation
oReinforcement Mechanisms strengthen the Dierences established during Isolation
oPre- & Post-zygotic Barriers are Reinforcing
0 or lower Fitness for breeding between the Descendant Gene Pool
Imperfectly separated Gene Pools
oReinforced by Pre- & Post-zygotic Barriers
o non-zero Fitness of Hybrids
oSometimes the Point of Contact is a Hybrid Zone
Hybrid Zone
oStable Hybrid Zone
Hybrids usually have Lower Fitness if the Zone is Stable
i.e. Persistent & NOT moving geographically
oMoving Hybrid Zone
Hybrids usually have Higher Fitness if the Zone is Moving
Hermits may ultimately disappear if this is a Moving Hybrid Zone
c.f.
Y chromosome is coming only from the male
Therefore, Y chromosome can be used as mtDNA
oY chromosome (male)
omtDNA (female)
First Generation Hybrids
50 : 50 nuclear DNA
100% Hermit mtDNA if the Female was a
Hermit Warbler
Character Displacement
oin case of Re-contact with 2 sister / sibling species which have overlapping
characteristics
oCompetition between 2 species (often Sister species)
oContinuing Divergence of some Key Traits
oDirectional Selection in 2 species in 2 Opposite Directions