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Lecture outline
Speciation
Species definitions
Keeping species separate
Modes of speciation
Macroevolution
What’s a species?
Species is Latin for ‘kind’ or ‘appearance’
Biologists have officially described MANY
species
 Roughly
 Is
1.6 million
there an official count?
 The
Catalogue of Life
1,606,554 species as of 2015
 Includes
A brief detour on writing
“Species” is both singular and
plural
Species names are written
using binomial nomenclature of
Latin or Latinized versions of
words
Genus species
The actual names are italicized
Genus is always capitalized
 species is always lower case


Pycnopsyche gentilis
Species concepts
Our ideas about how best to define a
species have changed over time
A challenge:
How can you tell when something is a
different ‘kind’ than something else?
Meadowlarks
 If
speciation is occurring, no species
concept will “work” all the time - you should
always be able to find arguable forms
Fig. 24.2a
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Morphological species concept
Morphological species concept
Any problems?
Defined by…
Type specimen
Morphospecies?
Diatoms
Biological species concept

Two types of biological barriers to reproduction
 Prezygotic vs. Postzygotic barriers
German ornithologist
Modern Synthesis
Population or group of populations
that have the potential to interbreed
in nature and produce viable, fertile
offspring (1942)
How related to ‘kinds’?
Gene flow?
Problems?
Fig. 24.3
Mayr on right
in New Guinea
Prezygotic barriers overview
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Fig. 24.2b
Reproductive isolation
Ernst Mayr (1904-2005)

Golden silk orb weaver
Nephila clavipes
Prezygotic barriers (1)
Habitat isolation
Notice anything
in common?
Three-spined stickleback species
differ by lake habitat: benthic vs.
pelagic zones
Fig. 24.3
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Prezygotic barriers (2)
Prezygotic barriers (3)
Behavioral isolation
Temporal isolation
Song
Song
Eastern meadowlark
Fig. 24.2a
winter
Fig. 24.3 c & d
summer
Prezygotic barriers (5)
Prezygotic barriers (4)
Mechanical isolation
Western meadowlark
Gametic isolation
F
M
Familiar bluet
pic by Giff Beaton
Fig. 24.3g
Robertson & Paterson 1982
Postzygotic barriers overview
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Postzygotic barriers (1)
Notice anything
in common?
Reduced hybrid viability: hybrid
offspring dies during development
Male hybrids
that die as larvae
Fig. 24.3
Drosophila
melanogaster
Drosophila
simulans
Hutter & Ashburner 1987
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Postzygotic barriers (2)
Postzygotic barriers (3)
Reduced hybrid fertility: hybrid
offspring are sterile
Dad
Hybrid breakdown:
hybrids are fertile,
but their offspring
either die or are
sterile
Mom
Horse + donkey = sterile mule
Hybrid
Fig. 24.3l
Several other species concepts have
been proposed
Modes of speciation
2 species from 1
Phylogenetic species concept


Minimum number of individuals that share a
common ancestor forming a branch on an
evolutionary tree
Ecological Species Concept

= cladogenesis
Allopatric vs.
sympatric
speciation
Group of organisms adapted to a particular set of
resources, called a niche, in the environment
Different species concepts agree most of the
time

They differ mostly when applied to borderline or
poorly understood cases
Fig. 24.5
Evidence for allopatric speciation
A. formosus
Sympatric speciation (1)
A. nuttingi
Cell
division
error
Habitat differentiation*
Sexual selection
Polyploidy
ATLANTIC OCEAN

2n = 6
80%(!) of plants
Isthmus of Panama
Autopolyploidy
Tetraploid cell
4n
Meiosis
PACIFIC OCEAN
2n
Snapping shrimp
vs.
Isthmus of Panama
Bread wheat
Fig.
Fig.24.6
24.8
A. panamensis
A. millsae
2n
Fig. 24.x
Gametes produced
by tetraploids
New species
(4n)
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Sympatric speciation (2)
Sympatric speciation (3)
Polyploidy in tree frogs
Cope’s gray tree frog
Hyla chrysocelis
Call
24
Diploid
Sexual selection/Mate choice
Gray tree frog
Hyla versicolor
Call
Tetraploid
What happens when allopatric
populations meet?
48
Cichlids
Fig. 24.11
Hybrid zones: Reinforcement
Hybrid zone formation
Males dissimilar;
Females correct
Males similar;
Females incorrect
Males of the pied flycatcher
look different depending on
whether the closely related
collared flycatcher is present
Fig. 24.13
Fig. 24.14
Hybrid zones: Fusion
Fig. 24.15
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