NEW AIM: What is a species? Carolus Linnaeus - Linnaeus used physical appearance to identify species...

NEW AIM: What is a species?

Carolus Linnaeus

- 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)

CHAPTER 14: The Origin of Species

Encyclopedia of life (www.eol.org)

http://www.eol.org/

AIM: What is a species?

- Problem: appearance is not always good at defining a species

Fig. 14.1A

Sturnella magna Sturnella neglecta(eastern meadowlark) (western meadowlark)


- Problem: appearance is not always good at defining a species

Fig. 14.1BHomo sapiens (Humans)


- 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


A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull, Larus fuscus (behind) in Poland

Ring Species

Reproductive isolation - prevents gene flow between species


A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull, Larus fuscus (behind) in Poland

Ring Species - may illustrate the process of speciation in action.



Fig. 14.1C

Ring Species - may illustrate the process of speciation



Ring Species - connected series of neighboring populations that can interbreed, but the two "end" populations are too distantly related to interbreed.



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


Biological species concept

Morphological species concept

- Ring species

- Asexual, Fossils

- binomial system

Linnaeus

- Taxonomy

SUMMARY

• 1860 - Some mosquitoes (Culex pipiens) migrated into the London Underground (subway) during its construction.

EXAMPLE:

NEW AIM: How do new species arise (speciation)?

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)



speciation

Reproductive barrier

Isolation of populations

Mutations might** lead to a…

**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

2. Postzygotic barriers

- prevent mating or fertilization

- 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

IMPORTANT: Populations may be able to breed successfully with each other if they were doing it at the same time.

Can they mate though if we put them together???


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.


3. Behavioral isolation - Little or no sexual attraction between males and females

- Male fireflies

- courtship rituals

- pheromones

- blink their light in particular patterns to attract females of their kind


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.


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.


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).


5. Gametic isolation4. Mechanical isolation3. Behavioral isolation2. Habitat Isolation1. Temporal isolation

SUMMARY

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


2. Hybrid sterility - Hybrids make it to maturity, but fail to produce functional gametes

Horse (female) + donkey (male) = mule (sterile)


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?

3. Hybrid Breakdown

2. Hybrid sterility

1. Hybrid inviability

SUMMARY


Review:


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?

How might a population fragment and become isolated from each other?

speciation


Isolation of populations


1. allopatric speciation:

Fig. 14.3

Mode of speciation caused by a geographic barrier isolating populations:

Explain why speciation does not always have to occur between allopatric populations.

**Must establish a reproductive barrier!!

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


Fig. 14.3

- Mountain range emerges- Large lakes break into smaller lakes

- Land bridge may form or disappear

(all depends on the species)

What types of geographic barriers can you think of?



Fig. 14.3


Geographically isolated antelope squirrels






When do you think allopatric speciation is most likely to occur?

When the isolated population is SMALL.

Ex. Galapagos finch species - all arose in less than 2 million years!

- genetic drift- natural selection


Fig. 14.4A



Galapagos - 14 finch species - all evolved from a single population that colonized one of the islands. How might this have happened?

Fig. 14.4A Fig. 14.4B




Fig. 14.4A Fig. 14.4B




Fig. 14.4A Fig. 14.4B




Fig. 14.4A Fig. 14.4B




Fig. 14.4A Fig. 14.4B



Adaptive radiation - emergence of numerous species from a common ancestor introduced to new and diverse environments

Why do you think that only ONE finch species is found on Cocos Island?



There is only one isolated island without geographic barriers to split the population in contrast to the Galapagos.




?

speciation




Reproductive barrier (isolation)

speciation

Geographic Isolation of populations


**Just because a population is split and the two populations are isolated from each other doesn’t mean that a reproductive barrier will arise.

Can you think of another way that speciation might occur other than through allopatric speciation?


- when reproductive isolation (barriers) arises without geographic separation.

- not widespread among animals

- very important in plants

*genetic change produces a reproductive barrier between new mutants and parent population


2. Sympatric speciation:

How might reproductive isolation arise within a population?

Plants -

- If this plant cell undergoes meiosis, what would be the ploidy of the resulting cells?



Haploid

Plants -

- What if an “accident” occurred during meiosis (total nondisjunction in meiosis II)?



Plants -



- What if an “accident” occurred during meiosis (total nondisjunction in meiosis II)? Diploid cells form

Plants -

If it happens in ovum and sperm, these gametes can now self fertilize…



Plants -

- Result: A Polyploid (tetraploid, 4n) offspring

Fig. 14.5A



(Plants are better able to deal with polyploidy than animals)

Plants -

How can the tetraploid reproduce?

Fig. 14.5A



Plants -

Meiosis of a tetraploid cell would generate diploid gametes.

Fig. 14.5A



Plants -- What if the tetraploid were to breed with the parent-type (diploid) organism?

Fig. 14.5A



Diploid (2n) gametes + haploid (n) gamete = triploid (3n) zygote (sterile)

Plants -- What if new tetraploid were to initially self fertilize and then the offspring mate?

Fig. 14.5A



Diploid (2n) ovum + Diploid (2n) sperm = tetraploid (4n) zygote

Result: INSTANT SPECIATION


Evolution of reproductive barriers in the lab:

Diana Dodd - Yale University

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).

Type of reproductive barrier?


SUMMARY1. Allopatric Speciation

2. Sympatric Speciation

- speciation due to geographic isolation

- speciation event within the population

- polyploidy in plants

- From a single individual

- Cross fertilization of different species

1. meiotic error (diploid becomes tetraploid)

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?

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?)

the “haploid” cell has an accident during MITOSIS or MEIOSIS (total nondisjunction)?

What if:

However: The plant may be able to reproduce asexually

Your now diploid (2n) and fertile!

Result: SPECIATION



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NEW AIM: What is a species? Carolus Linnaeus - Linnaeus used physical appearance to identify species...

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