Transcript AIM: By what means do reproductive barriers (speciation) arise?

CHAPTER 14: The Origin of Species
NEW AIM: What is a species?
- Linnaeus
used physical
appearance to identify
species when he developed
the binomial system of
naming organisms
- established the basis for
taxonomy
(classification of living organisms)
Encyclopedia of life (www.eol.org)
Carolus Linnaeus
AIM: What is a species?
- Problem:
appearance is not always good at
defining a species
Sturnella magna
(eastern meadowlark)
Fig. 14.1A
Sturnella neglecta
(western meadowlark)
AIM: What is a species?
- Problem:
appearance is not always good at
defining a species
Fig. 14.1B
Homo sapiens (Humans)
AIM: What is a species?
- So how should we define a species?
•The biological species concept - a population or
group of populations whose members can interbreed
and produce fertile offspring
AIM: What is a species?
Ring Species
A Herring Gull, Larus argentatus
(front) and a Lesser Black-backed
Gull, Larus fuscus (behind) in
Poland
Reproductive isolation - prevents gene flow between species
AIM: What is a species?
Ring Species - may illustrate the process of
speciation in action.
A Herring Gull, Larus argentatus
(front) and a Lesser Black-backed
Gull, Larus fuscus (behind) in
Poland
Reproductive isolation - prevents gene flow between species
AIM: What is a species?
Ring Species - may illustrate the process of
speciation
Fig. 14.1C
Reproductive isolation - prevents gene flow between species
AIM: What is a species?
Ring Species - connected series of neighboring
populations that can interbreed, but the two "end"
populations are too distantly related to interbreed.
Reproductive isolation - prevents gene flow between species
AIM: What is a species?
Does the biological species concept apply to
all organisms?
Does not apply to fossils or asexual organisms like bacteria.
The morphological species concept - used when the
biological species concept can’t be applied.
- classification based on observable and measurable
phenotypic traits
AIM: What is a species?
SUMMARY
Linnaeus
- binomial system
- Taxonomy
Biological species concept
- Ring species
Morphological species concept
- Asexual, Fossils
NEW AIM: How do new species arise (speciation)?
EXAMPLE:
• 1860 - Some mosquitoes (Culex pipiens) migrated
into the London Underground (subway) during its
construction.
AIM: How do new species arise?
Speciation - a gradual or rapid process?
• Mosquitos are isolated underground from parent
population above ground.
• New environment - new prey, mating habits, stable
temp., breeds all year long, etc…
• Natural selection, genetic drift, mutation, maybe SS
- The two populations were diverging.
• Biologists considered this population a different
species: Culex molestus
• Confirmed in 1999 when members of each population
were put together…no offspring produced!
AIM: How do new species arise?
Speciation - a gradual or rapid process?
• In less than 150 years, a new species emerged =
speciation.
• What had to happen for speciation to occur?
Isolation of populations- need to block
GENE FLOW between the populations!
- keep populations apart to prevent gene flow until
enough genetic changes occur in each making
them genetically incompatible
(a reproductive barrier if formed)
AIM: How do new species arise?
Isolation of populations
Mutations might**
lead to a…
Reproductive barrier
speciation
**Just because a population is split and the two populations are isolated from
each other doesn’t mean that a reproductive barrier will arise.
NEW AIM: What types of reproductive
barriers exist to keep species apart?
Reproductive barrier A biological feature of the organism that prevents it from
interbreeding with closely related species
Two general types:
1. Prezygotic barriers - prevent mating or fertilization
2. Postzygotic barriers - prevent the development of
fertile adults
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
1. Temporal isolation - two species breed at different times
(day, week, season) (mating or
flowering)
Eastern and Western spotted skunk territories overlap.
- Eastern skunks breed only in late winter
- Western skunks breed only in fall
Can they mate though if we put them together???
IMPORTANT: Populations may be able to breed successfully with
each other if they were doing it at the same time.
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
2. Habitat isolation - populations live in same general area,
but not in the same kinds of places (do
not meet)
- Herbivorous insects feed and mate on different host
plants.
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
3. Behavioral isolation - Little or no sexual attraction between
males and females
- Male fireflies - blink their light in particular patterns
to attract females of their kind
- courtship rituals
- pheromones
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
4. Mechanical isolation - Structural differences in genitalia or
flowers prevent copulation of pollen
transfer
- many insects have reproductive organs that fit like
complicated puzzle pieces - only male and female of
same species match up.
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
4. Mechanical isolation - Structural differences in genitalia or
flowers prevent copulation or pollen
transfer
- many flowering plants have
flower structures adapted for
only a specific animal
pollinator that will transfer
pollen only between same
species.
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
5. Gametic isolation - Male or female gametes die before
uniting or fail to unite
- many mammals - sperm cannot survive in female of a
different species
- male and female sea urchins dump their sperm and eggs
into the water. Only same species sperm and egg can fuse
(appropriate ligand and receptor proteins).
AIM: What types of reproductive barriers
exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization
SUMMARY
1. Temporal isolation
2. Habitat Isolation
3. Behavioral isolation
4. Mechanical isolation
5. Gametic isolation
AIM: What types of reproductive barriers
exist to keep species apart?
Postzygotic barriers - prevent development of fertile adults
1. Hybrid inviability - Hybrid zygotes fail to develop or to
reach sexual maturity
- genes not compatible
Ex. Hybrid between the frogs Rana pipiens and Rana sylvatica
do not survive more than a day or so.
Rana pipiens
Rana sylvetica
AIM: What types of reproductive barriers
exist to keep species apart?
Postzygotic barriers - prevent development of fertile adults
2. Hybrid sterility
- Hybrids make it to maturity, but fail
to produce functional gametes
Horse (female) + donkey (male) = mule (sterile)
AIM: What types of reproductive barriers
exist to keep species apart?
Postzygotic barriers - prevent development of fertile adults
3. Hybrid Breakdown - Hybrid mates, but offspring of
hybrids are weak and infertile
- hybrids can reproduce, but their offspring cannot (feeble
or sterile).
-Happens more in plants than animals.
Ex. certain species of cotton plants
AIM: What types of reproductive barriers
exist to keep species apart?
SUMMARY
1. Hybrid inviability
2. Hybrid sterility
3. Hybrid Breakdown
AIM: What types of reproductive barriers
exist to keep species apart?
Review:
AIM: What types of reproductive barriers
exist to keep species apart?
Question
Two closely related tropical bird species live in the same
forest, but one feeds and mates in the forest canopy and the
other on the forest floor. What type of reproductive barrier is
this an example of?
Habitat Isolation
NEW AIM: By what means do reproductive
barriers (speciation) arise?
Isolation of populations
Mutations might**
lead to a…
Reproductive barrier
speciation
How might a population fragment and become
isolated from each other?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Mode of speciation caused by a geographic barrier isolating
populations:
Explain why speciation does not always have to
occur between allopatric populations.
Fig. 14.3
**Must establish a reproductive barrier!!
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
What types of geographic barriers can you think of?
- Mountain range emerges
- Large lakes break into smaller lakes
- Land bridge may form or disappear
(all depends on the species)
Fig. 14.3
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
What types of geographic barriers can you think of?
Fig. 14.3 Geographically isolated antelope squirrels
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
What types of geographic barriers can you think of?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
When do you think allopatric speciation is most likely to occur?
When the isolated population is SMALL.
- genetic drift
- natural selection
Ex. Galapagos finch species - all arose
in less than 2 million years!
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Galapagos - 14 finch species - all evolved from a single
population that colonized one of the islands. How might this
have happened?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Fig. 14.4B
Galapagos - 14 finch species - all evolved from a single
population that colonized one of the islands. How might this
have happened?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Fig. 14.4B
Galapagos - 14 finch species - all evolved from a single
population that colonized one of the islands. How might this
have happened?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Fig. 14.4B
Galapagos - 14 finch species - all evolved from a single
population that colonized one of the islands. How might this
have happened?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Fig. 14.4B
Galapagos - 14 finch species - all evolved from a single
population that colonized one of the islands. How might this
have happened?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Fig. 14.4A
Fig. 14.4B
Adaptive radiation - emergence of numerous species from a
common ancestor introduced to new and diverse environments
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Why do you think that only ONE finch species is found on Cocos Island?
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
There is only one isolated island without geographic barriers to split the population in
contrast to the Galapagos.
AIM: By what means do reproductive barriers
(speciation) arise?
?
Reproductive barrier
speciation
AIM: By what means do reproductive barriers
(speciation) arise?
1. allopatric speciation:
Geographic Isolation of populations
Mutations might**
lead to a…
Reproductive barrier (isolation)
speciation
**Just because a population is split and the two populations are isolated from
each other doesn’t mean that a reproductive barrier will arise.
AIM: By what means do reproductive barriers
(speciation) arise?
Can you think of another way that speciation might
occur other than through allopatric speciation?
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
- when reproductive isolation (barriers) arises without
geographic separation.
- not widespread among animals
- very important in plants
How might reproductive isolation arise within a population?
*genetic change produces a reproductive barrier between
new mutants and parent population
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - If this plant cell undergoes meiosis, what would be
the ploidy of the resulting cells? Haploid
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - What if an “accident” occurred during meiosis (total
nondisjunction in meiosis II)?
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - What if an “accident” occurred during meiosis (total
nondisjunction in meiosis II)? Diploid cells form
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants If it happens in ovum and sperm, these gametes can
now self fertilize…
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - Result:
A Polyploid (tetraploid, 4n) offspring
(Plants are better able to deal with polyploidy than animals)
Fig. 14.5A
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants How can the tetraploid reproduce?
Fig. 14.5A
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants Meiosis of a tetraploid cell would generate diploid gametes.
Fig. 14.5A
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - What if the tetraploid were to breed with the parent-type
(diploid) organism?
Diploid (2n) gametes + haploid (n) gamete = triploid (3n) zygote (sterile)
Fig. 14.5A
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - What if new tetraploid were to initially self fertilize and then
the offspring mate?
Diploid (2n) ovum + Diploid (2n) sperm = tetraploid (4n) zygote
Result: INSTANT SPECIATION
Fig. 14.5A
AIM: By what means do reproductive barriers
(speciation) arise?
Evolution of reproductive barriers in the lab:
Type of reproductive barrier?
Behavioral isolation
- Perhaps alleles that enhance
digestion of starch or maltose also
effect (or are linked to) the alleles
that code for enzymes that make
molecules that function in mate
recognition (pheromones).
Diana Dodd - Yale University
AIM: By what means do reproductive barriers
(speciation) arise?
SUMMARY
1. Allopatric Speciation
- speciation due to geographic isolation
2. Sympatric Speciation
- speciation event within the population
- polyploidy in plants
- From a single individual
1. meiotic error (diploid becomes tetraploid)
- Cross fertilization of different species
1. cross fertilization (new haploid)
2. meiotic error (becomes diploid)
Punctuated vs. Gradualistic model
Gradualistic model
Punctuated model
Punctuated vs. Gradualistic model
Question: Which model would account for the relative rarity of
transition fossils linking newer species to older ones?
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation:
Plants - What if instead of a single species mating with itself to
make a polyploid, two somewhat related species were to
mate?
Result: Plant is usually sterile (chromosomes are not homologous)
(How many sets of chromosomes does this new plant have?)
Result: SPECIATION
However: The plant may be able to reproduce asexually
What if: the “haploid” cell has an accident during MITOSIS or
MEIOSIS (total nondisjunction)?
Your now diploid (2n) and fertile!
AIM: By what means do reproductive barriers
(speciation) arise?
2. Sympatric speciation: