Download Chapter 24: The Origin of Species

Chapter 24: The Origin of
Species
Macroevolution
Cumulative
of time
effects of speciation over vast amounts
Anagenesis/phyletic
evolution
Gradual
accumulation of changes transform a
single species
Cladogenesis/branching
Splitting
evolution
of a gene pool
*single species morphs & diverges into 2 or more
species
CLADOGENESIS INCREASES BIODIVERSITY
Defining a species

Morphological species concept
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Paleontological species concept
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Focuses on morphologically discrete species
known only in the fossil record
Ecological species concept
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Based on body shape, size, & features
Views species in terms of its niche
Phylogenetic species concept

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Species is defined by its unique genetic
history on the tree of life
Compares physical & molecular sequences
Speciation

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New species adds to biological diversity
Species

Biological species concept

Populations whose members are reproductively
compatible and offspring viable and fertile
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Limitations: prokaryotes, fossil species, & relatively
unknown species
Reproductive isolation

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biological factors (barriers) that impede 2
populations from producing viable, fertile
hybrids
Pre-zygotic barriers
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Impede mating or hinder fertilization
Includes habitat, temporal, behavioral,
mechanical, & gametic isolation
Postzygotic barriers

Non-viable or sterile hybrid
Allopatric speciation

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Geography divides a population & its gene
pool
Isolated populations evolve by natural
selection & genetic drift, resulting in
reproductive isolation
Sympatric speciation
(species exist in same geographically overlapping region)

Speciation occurs as a result of
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chromosomal changes
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Polyploidy
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Autopolyploid- more than 2 chromosome sets from one
species
Allopolyploid- more than 2 chromosome sets from more
than one species
 Often used to create new desirable crops
non-random mating

Female selects male based on appearance
Evolutionary trends
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Gradualism
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Punctuated equilibrium
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Species descend from a common ancestor
Gradually diverge as changes accumulate & unique
adaptations are acquired
Long periods of no apparent change in species
followed by abrupt change
***Change may not be as dramatic as fossil record
suggests
Adaptive radiation

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Common ancestor exists for many diversely adapted
species
Diversity occurs when groups are introduced into new
environments when:

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A few organisms migrate
Environment changes opening up new niches
Evolutionary change

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Evolution of complex traits may occur
incrementally
Each step on path to complexity must be
of benefit to organism

Exaptation- structures that take on a new role
in addition to initial role in ancestor specie
Evolutionary change

Heterochrony

Evolutionary change in the rate or timing
of developmental events Allometric growth
Proportioning that gives a body specific form
 Change in timing of development has
significant morphological impact
 Ex. Salamander feet (ground vs. tree
dwelling)

 Paedomorphosis

Reproductive development accelerates vs.
somatic development; sexually mature adult
retains juvenile features of ancestor
Evolutionary change

Change in Homeotic genes

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Results in substantial evolutionary change in
placement & spatial organization of body
parts
**Large changes in appearance may
result from small genetic change!!
Species selection

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Species that endure the longest appear to
give direction to evolutionary “trend” even
though other features existed
Ex. Evolution of horses