Species and Speciation
BIOL 1407
Biological Species Concept
• A group of
organisms that
can interbreed
and produce
viable, fertile
offspring
•
Photo Credit of Galápagos Marine Iguanas:
Putneymark, 2008, Wikimedia Commons
Biological Species Concept
• Assumes
– Common
characteristics
– Genetically compatible
– Interbreed under
natural conditions
– Sexual Reproduction
•
Photo Credit of Iguana iguana: Ianare, 2007, Wikimedia
Commons
Drawbacks of
Biological Species Concept
• Cannot be used with
exclusively asexual
organisms
– Prokaryotes
– Amoeba & some
other protists
– Some animals,
plants & fungi
•
Photo Credit of Amoeba proteus: Angel, BIOL 1407
student, fall 2008
Drawbacks: Isolated Populations
• How do you test for
interbreeding under
natural conditions?
• Can a deer in
Florida interbreed
with one in
Wisconsin?
•
•
Photo Credit of Key Deer: Scott Bauer, 2006, USDA
Photo Credit of Deer Running: Paul Frank, 2006, USFWS
Drawbacks
• Can a Great Dane
interbreed with a
Chihuahua?
•
Photo Credit: David Shankbone, 2006, Wikimedia
Commons
Drawbacks
• Some species look
and behave
differently
• Can interbreed and
have viable, fertile
offspring
• Example: coyotes,
wolves, dogs
•
Picture Credits: Courtesy of Smithsonian National
Zoo @ nationalzoo.si.edu (coyote and wolf); Pam
Wolfe (dog)
Drawbacks:
Horizontal Gene Transfer
• Vertical gene transfer
 Parents  offspring
• Horizontal gene transfer
 Individual  individual
 Not parent-offspring
•
Diagram Credit: Gregorius Pilosus, 2009, Wikimedia Commons
Horizontal Gene Transfer
• Can occur between
organisms:
– Different species
– Different kingdoms
– Different domains
•
Diagram Credit: Barth F. Smets, Ph.D., with
permission, 2005, Wikimedia Commons
Horizontal Gene Transfer
in Bacteria
(1) Transformation
Horizontal
Gene Transfer
in Bacteria
(2) Transduction
Horizontal Gene Transfer
in Bacteria
(3) Conjugation
Horizontal Gene Transfer
• E. coli 0157:H7
has picked up
Shiga toxin gene
from Shigella
• Up to 25% genetic
difference among
E. coli strains
•
Photo Credit of E. coli 0157:H7: E. H. White,
Centers for Disease Control, 1995,
Wikimedia Commons
Horizontal Gene Transfer
• Normally, 25%
genetic diversity 
different species
• Human and chimp
genomes differ by
only 1.2%
•
Photo Credit: Thomas Lersch, 2005, Wikimedia
Commons
Drawbacks: Fossil Species
• Cannot tell if
fossil
organisms
were capable
of
interbreeding
•
Photo Credit of Harlan’s Ground
Sloth: Doyle Cross, 2006, UT
Memorial Museum
Fossils
• Normally can’t
compare genes
of different
fossil species
Morphological Species Concept
• Group of individuals
that share common
characteristics
• Used for:
• Fossils
• Exclusively asexual
• Traditional method
for sexual organisms
•
Photo Credit of Orchid: Bernd Haynold, 2004, Wikimedia
Commons
Biological Species Concept:
Reproductive Isolation
• Barriers between species
• Prevent viable fertile
offspring
•
Photo Credit (Lesser Bird of Paradise): Roderick Eime, 2005; (Greater
Bird of Paradise): Andrea Lawardi, 2008, Wikimedia Commons
Reproductive Isolating
Mechanisms
• Prezygotic mechanisms
– Before fertilization
• Postzygotic mechanisms
– After fertilization
Prezygotic Mechanisms
• Prevents:
– Prevent mating from
occurring
– Prevents gametes
from forming a
zygote
•
Photo Credit for Sperm fertilizing an ovum: Wikimedia
Commons, 2008
Prezygotic Mechanisms:
Temporal Isolation
• Isolated by time
• May breed:
– Different times of day
– Different seasons
– Different years
•
Photo Credit: Alan Zomerfeld, 2006, Wikimedia Commons
Temporal Isolation
Late Winter
Late Summer
Prezygotic Mechanisms:
Habitat Isolation
• Same geographic area
• Different habitats
Prezygotic Mechanisms:
Behavioral Isolation
• Different
courtship rituals
• Blue-Footed Booby Video:
http://www.youtube.com/watch?v=4
MPfTzXEZdY
•
Photo Credit: Richard001, 2007, Wikimedia Commons
Behavioral Isolation
Eastern and Western Meadowlarks
• Isolated by Songs
•
Listen to both species (Links to songs are below the picture):
•
http://www.lewis-clark.org/content/content-article.asp?ArticleID=401
Prezygotic Mechanisms:
Mechanical Isolation
• Structural
differences
prevent mating
• Example:
Genital openings
(arrows) not
aligned  No
Mating
Prezygotic Mechanisms:
Gametic Isolation
• Sperm cannot
fertilize eggs
• Very important in
aquatic species
(broadcast
spawners)
• Example: Sea Urchins
Postzygotic Mechanisms
• Prevents hybrid
zygotes from
developing into
viable, fertile adults
•
Photo Credit of Zeedonk: Ondrejk, 2004,
Wikimedia Commons
Postzygotic Mechanism:
Reduced Hybrid Viability
• If Sheep and
goats mate 
Hybrid zygotes
• Die before birth.
•
Photo Credit: Missouri NRCS Photo
Gallery
Postzygotic Mechanism:
Reduced Hybrid Fertility
• Male donkey x
Female horse
Mule
• Mules:
– Healthy (viable)
– Sterile.
Postzygotic Mechanism:
Hybrid Breakdown
• First generation
hybrids are
viable and
fertile.
• Offspring of
hybrids are
feeble or sterile.
Speciation
• Process of species formation
• Two main mechanisms:
– Allopatric speciation
– Sympatric speciation
Allopatric Speciation
Geographic separation
  Genetic
exchange
 Populations
become genetically
different
 Reproductive
isolation
Sympatric Speciation
• Populations not
geographically
separated
• Can be due to
rapid genetic
changes:
– Alter morphology
– Alter behavior
– Alter habitat
preferences
Example: Sympatric Speciation
• Euhadra snails
• Mutation in one
gene  Shell
spirals in opposite
direction
• Instant mechanical
isolation
 Two species
Adaptive Radiation
• A common ancestor
 Many new species
• Relatively rapid
• Common in island
chains
– Isolated
– Numerous habitats &
resources
•
Map Credit: M. Minderhoud, 2006, Wikimedia Commons
Galápagos Finches
• Ancestral finch from
South America 
Several finch
species
– Different diets
– Different beak
shapes
– Different beak sizes
Galápagos Finches
Hawaiian Silverswords
• Tarweed arrived
from North
America ~ 5 mya
• Common
ancestor 
Silverswords
•
Map Credit: M. Minderhoud, 2006, Wikimedia
Commons
Hawaiian Silverswords
The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.