Download Origin of species

9/15/2014
What is a species?


The origin of
species
Chapter 24
A species is a “kind” of organism
According to the Biological Species Concept,
a species is a group of populations whose
members have the potential to interbreed in
nature and produce viable, fertile offspring;
they do not breed successfully with other
populations


have morphological,
physiological, biochemical and DNA
sequence differences
Reproduction isolation is critical to this concept
Gene flow holds a population together
genetically
 Species
Types of reproductive barriers
 Pre-zygotic
 Post-zygotic
Habitat isolation
 Two
species
living in
different
habitats may
not encounter
each other
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Temporal isolation
 Brown
trout breed in the fall whereas
rainbow trout living in the same streams
breed in the spring
Mechanical isolation
 Reproductive
parts do not fit together
Behavioral isolation
 Mating
cues are usually specific
Gametic isolation
 Sperm
cannot fertilize egg
Egg
Reduced hybrid viability
 Hybrids
are frail and have low survival
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Reduced hybrid fertility
 Hybrids
can
be infertile
Other species concepts
 Morphological species
concept
 Ecological species concept
 Phylogenetic species concept
Hybrid breakdown
 Hybrid
vigor
reduced in
subsequent
generations
Mechanisms of
speciation
 Speciation
occurs when
gene flow is
interrupted


Predation selects for different
body shapes in different
habitats
Allopatric
Sympatric
Separate populations may evolve
independently through mutation,
natural selection, and genetic drift
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Geographic isolation increases
reproductive isolation
Sympatric species
Polyploidy
 Gene
 Extra



flow discontinued through
Polyploidy
Habitat differentiation
Sexual selection
Autopolyploidy
 Extra
chromosomes
derived from within a
species
set of chromosomes through an error
during cell division
 More common in plants
Allopolyploidy
 Extra
chromosomes
derived from more
than one species
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Habitat differentiation
Sexual selection
 Female
Reproductive isolation can be
controlled by a single locus
ore more than one
Speciation can be fast or slow
Ecological isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Thermal isolation
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If a certain group of organisms evolve via
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intermediate forms in the fossil record?
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The hybrid sterility of a hinny (cross between a
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example of a prezygotic isolation mechanism.
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Behavioral isolation
Mechanical isolation
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Temporal isolation
Behavioral isolation
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Lions and tigers can mate but in the wild they
occupy different portions of the landscape
(grasslands vs. forests), what force maintains their
20% 20% 20% 20%
genetic isolation?
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Closely related species that have
different mating rituals are example of
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