Download Speciation Lecture Speciation_Lecture

Big Ideas
 1.C.1) Speciation and extinction have occurred
throughout Earth’s history.
 1.C.2) Speciation may occur when two populations
become reproductively isolated from each other.
 1.C.3) Populations of organisms continue to evolve.
Illustrative Examples:
o Five major extinctions (25.4)
o Human impact on ecosystems and species extinction
rates
o Directional phenotypic changes (e.g. Finch beaks)
© 2011 Pearson Education, Inc.
lecture outline
o The biological species concept emphasizes reproductive
isolation.
o Speciation can take place with or without geographic separation.
o Hybrid zones reveal factors that cause reproductive isolation.
o Speciation can occur rapidly or slowly and can result from
changes in few or many genes.
[1] Biological
Species
Concept
 A biological species is a group of
populations whose individuals
have the potential to interbreed
and produce viable (living), fertile
offspring with each other but not
with members of other species.
No Reproductive Isolation
Canis familiaris
Subpopulation #1
Canis familiaris
Subpopulation #2
Reproductive Isolation
Canis familiaris
Subpopulation #1
Canis familiaris
Subpopulation #2
So what’s getting in the way?
Potentially, a lot of things…
Reproductive Isolating Mechanisms
 Reproductive isolation occurs when populations are divided
in some way and can no longer interbreed.
 Any heritable feature of body, form, functioning, or behavior
that prevents breeding between one or more genetically
divergent populations can cause reproductive isolation.
 There are Prezygotic or Postzygotic mechanisms.
 Please refer to handout Figure 24.3 Exploring Reproductive
Barriers.
Reproductive Isolating Mechanisms
 Reproductive isolation occurs when populations are divided
in some way and can no longer interbreed.
 Any heritable feature of body, form, functioning, or behavior
that prevents breeding between one or more genetically
divergent populations can cause reproductive isolation.
 There are Prezygotic or Postzygotic mechanisms.
 Please refer to handout Figure 24.3 Exploring Reproductive
Barriers.
Reproductive Isolating Mechanisms
 Reproductive isolation occurs when populations are divided
in some way and can no longer interbreed.
 Any heritable feature of body, form, functioning, or behavior
that prevents breeding between one or more genetically
divergent populations can cause reproductive isolation.
 There are Prezygotic or Postzygotic mechanisms.
 Please refer to handout Figure 24.3 Exploring Reproductive
Barriers.
A Wrench in the works…
Pre-zygotic Barriers
 Habitat Isolation
 Temporal Isolation
 Behavioral Isolation
 Mechanical Isolation
 Gametic Isolation
Postzygotic Barriers
 Reduced Hybrid Viability
 Reduced Hybrid Fertility
 Hybrid Breakdown
A Wrench in the works…
Pre-zygotic Barriers
 Habitat Isolation
 Temporal Isolation
 Behavioral Isolation
 Mechanical Isolation
 Gametic Isolation
In any of these cases two
possible mating partners never
get to first base. Even if they
try to do so, fertilization never
happens.
Postzygotic Barriers
 Reduced Hybrid Viability
 Reduced Hybrid Fertility
 Hybrid Breakdown
Invariably, offspring are feeble,
sterile and even if F1 is fertile,
F2 isn’t.
Not a pretty picture!
Pre-zygotic Barriers
Great Dane
?
Chihuahua
Post-zygotic Barriers
Ensatina salamanders remain isolated
based on their habitats. Some hybridization occurs along adjacent borders.
Infertile mule (offspring of horse, donkey)
Reproductive Isolation
Ursa arctos
Ursa maritimus
Hybridization: closely related species attempting to
produce viable, fertile offspring.
Ursa arctos
Ursa maritimus
[1] Biological Species Concept
 Although helpful in thinking about how speciation occurs, the
biological species concept has limitations:
 It cannot be applied to organisms known only as fossils or to
organisms that reproduce only asexually. Thus scientists use
other species concepts like morphology (body structure) in some
cases.
lecture outline
o The biological species concept emphasizes reproductive
isolation.
o Speciation can take place with or without geographic separation.
o Hybrid zones reveal factors that cause reproductive isolation.
o Speciation can occur rapidly or slowly and can result from
changes in few or many genes.
Mr. Anderson says…
Allopatric
“Other
country”
Parapatric
Sympatric
“Same
country”
Speciation Processes
Main Modes of Speciation
http://www.all-about-reptiles.com/convergent-evolution.html
“The study of evolution has led scientists to discover some very
interesting evolutionary trends in nature. Similar species that used to
look more alike than they do now underwent divergent evolution;
species that used to look different but now share really similar
characteristics underwent convergent evolution; totally different
species that evolved together underwent co-evolution.
Brown Bears and Polar Bears illustrate divergent evolution. Scientists think that a long time ago a group of Brown Bears (bottom) became geographically
separated from the rest. This isolated group acquired new characteristics, such as the ability to eat meat, blubber to keep warm in snowy weather, and a
white coat for camouflage. They slowly evolved into Polar Bears.
http://www.duq.edu/sepa/regmed/evolution/aspects.shtml
[2] Speciation & Geographic Isolation
 In allopatric speciation, gene flow is reduced when two
populations of one species becomes geographically
separated from each other.
 One or both populations may undergo evolutionary change
during the period of separation, resulting in the establishment
of prezygotic or postzygotic barriers to reproduction.
Main Modes of Speciation
[2] Speciation & Geographic Isolation
 In parapatric speciation (a special case of allopatric
speciation), populations mate only with those nearest to
them; kind of opportunistic and lazy!
 Another example…
Main Modes of Speciation
[2] Speciation & Geographic Isolation
 In sympatric speciation, a new species originates while
remaining in the same geographic area as the parent
species.
 Plant species (and, more rarely, animal species) have
evolved sympatrically through polyploidy. Sympatric
speciation can also result from habitat shifts and sexual
selection.
lecture outline
o The biological species concept emphasizes reproductive
isolation.
o Speciation can take place with or without geographic separation.
o Hybrid zones reveal factors that cause reproductive isolation.
o Speciation can occur rapidly or slowly and can result from
changes in few or many genes.
[3] Hybrid zones  reproductive isolation
 Many groups of organisms form hybrid zones in which
members of different species meet and mate, producing at
least some offspring of mixed ancestry.
[3] Hybrid zones  reproductive isolation
 Possible Outcomes:
 Reinforcement: barriers are strengthened and hybrids cease to be
formed
 Fusion: two species continue “interspecies breeding” and become a
single unified species (some call this reverse speciation).
 Stability: hybrids continue to be produced but “parent species”
remain separate
lecture outline
o The biological species concept emphasizes reproductive
isolation.
o Speciation can take place with or without geographic separation.
o Hybrid zones reveal factors that cause reproductive isolation.
o Speciation can occur rapidly or slowly and can result from
changes in few or many genes.
[4] Pace of Speciation
 New species can form rapidly once divergence begins- but it
can take millions of years for that to happen.
 Certain catastrophic events are thought to accelerate the rate
of change among populations.
 The time interval between speciation events varies
considerably, from a few thousand years to tens of millions of
years.
http://ai.stanford.edu/~serafim/CS374_2006/notes/lecture24.pdf
http://www.google.com/imgres?imgurl=http://www.accessexcellence.org/BF/bf02/klein/slides/PhyloftheHom.gif&imgrefurl=http://www.ecotao.com/ho
Selected Practice Exam Questions
o3
o 10-11
o 13
o 23
o 30