Bio 122- exam 3 - Macroevolution

Macroevolution

the major changes in the history of life, are usually evident in the fossil record, includes

Macroevolution

Origin of new species:

•generates biological diversity

Macroevolution
2. –Origin of evolutionary novelty

•any newly acquired structure or property that permits the performance of a new function: ex. wings on birds and big brains in humans

Macroevolution

3. Explosive diversification following evolutionary breakthrough

•Thousands of plant species after the flower evolved

Macroevolution

4. mass extinctions

•explosion of mammals following dinosaur extinction

speciation

The formation of new species

occurs when 1 or more new species branch from a parent species.

speciation

speciation

Types:

Nonbranching evolution

branching evolution

speciation

Nonbranching evolution

(a)can transform a population but does not create new species.

speciation

branching evolution

(a)splits a lineage into 2 or more species.

a Latin word meaning “kind” or “appearance”

Species

One way of defining a species:

biological species concept

It defines a species as a population or group of populations whose members can interbreed to produce fertile offspring.

It defines a species as a population or group of populations whose members can interbreed to produce fertile offspring.

1. . Based on classification

§observable and measurable physical traits.

It defines a species as a population or group of populations whose members can interbreed to produce fertile offspring.

2. . Based on ecological niche

An ecological niche describes how an organism or population responds to the distribution of resources and competitors.

In other words, how an organism makes a living.

ecological niche

describes how an organism or population responds to the distribution of resources and competitors.

Biologists have developed other ways of defining species.

3. Based on genetic history:

should have identical genomes

Biologists have developed other ways of defining species.

1. —> 2. —>3.

1. classification —> ecological niche —> genetic history

The Origin of Species

What prevents biological species that are closely related from interbreeding?

For example, what maintains the species boundary between the Western spotted skunk and the Eastern spotted skunk?

Their geographic ranges overlap in the Great Plains region.

They appear similar and yet cannot interbreed.

Reproductive barriers

isolate the gene pools of species

We classify the barriers as either

prezygotic, postzygotic

The barriers will block interbreeding before (pre-) or after (post-) the 

formation of zygotes (fertilized eggs)

Prezygotic barriers

žprevent mating or fertilization between species

–The barrier may be time based (temporal isolation)

Prezygotic barriers

Prezygotic Barriers

temporal isolation:

time-based barrier keeps the species from mating even though they coexist on the Great Plains.

Prezygotic Barriers

habitat isolation

In other cases, species live in the same region but not in the same habitats

Prezygotic Barriers

habitat isolation

example:

one species of North American garter snake lives mainly in water, while a close relative lives on land

Prezygotic Barriers

behavioral isolation

Traits that enable individuals to recognize potential mates can function as reproductive barriers such as odor, coloration or courtship ritual

Prezygotic Barriers

behavioral isolation

in many bird species, courtship behavior is so elaborate that individuals are unlikely to mistake a bird of a different species as their own

Prezygotic Barriers

These blue-footed boobies, inhabitants of the Galapagos Islands, will mate only after a ritual of courtship displays.

§Here we see a male doing a high-step, a dance that advertises the bright blue feet to the female.

(mating rituals that must be preformed perfectly)

As a result, if the dance is not done correctly this could serve as a behavioral barrier between species.

Prezygotic Barriers

mechanical isolation

In some cases, male and female sex organs of different species are anatomically incompatible

Prezygotic Barriers

mechanical isolation

–For example, insects of closely related species try to mate but the organs may not fit together correctly and no sperm is transferred.

–However, individuals of different species may actually copulate, but their gametes are incompatible and fertilization does not occur.

Postzygotic barriers

§mechanisms that operate should interspecies mating occur and form “hybrids.”

Postzygotic barriers

hybrid

means an egg comes from 1 species and the sperm from another

Postzygotic barriers

Hybrid inviability

an example of a postzygotic barrier. This is when offspring fail to develop or fail to reach reproductive maturity

Postzygotic barriers

Hybrid inviability

Example: 

,although certain closely related frog species will hybridize, the offspring fail to develop normally.

§In other cases, offspring grow up to become adults, but remain infertile.

Postzygotic Barriers

Hybrid sterility

another example of a postzygotic barrier

Postzygotic Barriers

By crossing a female horse with a male donkey, you will produce a sterile mule.
A mule is an example of a

hybrid offspring

Hybrid breakdown

our last example of a postzygotic barrier.

Hybrid breakdown

There are some cases when 1^st generation hybrids are viable and fertile. However, when these hybrids mate with one another or with their parents,

−their offspring (2^nd generation) will become feeble or sterile.

Hybrid breakdown

In agriculture, crossing different species of cotton plants can produce fertile hybrids. But when these hybrids mate with one another

the offspring do not survive.

Mating 

Individuals of different species —> Mating attempt —>

fertilization (zygote forms)  —>viable, fertile offspring 

Prezygotic barriers

Temporal isolation

habitat isolation

Behavioral isolation

Mechanical isolation

Gametic isolation

Prezygotic barriers

Individuals of different species

Temporal isolation

Mating of flowering occurs at different season or times of day

Prezygotic barriers

Individuals of different species

Habitat isolation

Populations live in different habitats and do not meet

Prezygotic barriers

Individuals of different species

Behavioral Isolation

Little or no sexual attraction exists between populations

Prezygotic barriers

Matting Attempt

Mechanical isolation 

Structural differences in genitalia or flower precent copulation or pollen transfer

Prezygotic barriers

Matting Attempt

Gametic isolation

female and male gametes do not unite in fertilization

Postzygotic barriers

fertilization (zygote forms)

Hybrid inviablility

hybrid zygotes do not develop or do not reach sexual maturity

Postzygotic barriers

fertilization (zygote forms)

Hybrid sterility

Hybrids do not produce functional gametes

Postzygotic barriers

fertilization (zygote forms)

Hybrid breakdown

Hybrids are feeble or sterile

It is important to understand that it’s not usually a single reproductive barrier but a )____________ that reinforces the separation of species.

combination of 2 or more

The evolution of these reproductive barriers is

key to the origin of new species.

key to the origin of new species.

allopatric speciation

sympatric speciation.

Two Modes of Speciation

allopatric speciation

the initial block to gene flow is a geographic barrier that physically isolates the splinter population from other populations of the parent species.

Two Modes of Speciation

sympatric speciation

the origin of a new species without geographic isolation.

Two Modes of Speciation

The splinter population becomes

reproductively isolated right in the midst of the parent population.

Two Modes of Speciation

sympatric Speciation

original population —> initial step of speciation —> evolution of reproductive isolation —> speciation: 2 new species

Two Modes of Speciation:

Block to gene flow due to geographic barrier (ex. Mountain range)

No block to gene flow

žSeveral kinds of geologic processes can fragment a population into 2 or more isolated populations.

–A mountain may emerge and split a population of organisms.

–

–A land bridge, such as the Isthmus of Panama, may form and separate the marine life on either side.

–

–Even without geologic changes, geographic isolation and allopatric speciation  can occur if individuals colonize a new remote area away from the parent population.

Allopatric Speciation

Original population —> geographic barrier —> reproductive isolation —> speciation

Allopatric Speciation

geographic barrier

Once some kind of barrier is in place, speciation is only a matter of time

Allopatric Speciation

geographic barrier

Harris’ antelope squirrel (left) is found on the south rim of the Grand Canyon.

Just a few miles away on the north rim is the white-tailed antelope squirrel (right).

Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon.

How formidable must a geographic barrier be to keep allopatric populations apart?

The answer depends partly on the ability of the organisms to move.

How formidable must a geographic barrier be to keep allopatric populations apart?

§The answer depends partly on the ability of the organisms to move.

§Birds, mountain lions, and coyotes can cross mountain ranges, rivers and canyons.

§Windblown pollen and the seeds of plants can be carried on the backs of animals.

§However, small rodents may find the Grand Canyon a formidable barrier and would never be able to cross.

žThe likelihood of allopatric speciation increases when a population is both small and isolated.

example:

−For example, in less than 2 million years, the few animals and plants that successfully colonized the Galapagos Islands gave rise to all the species present there today.

The likelihood of allopatric speciation increases when

a population is both small and isolated.

§How can a population become reproductively isolated while in the midst of its parent population?

This can occur if a genetic change produces a reproductive barrier between mutants and the parent population.

§How can a population become reproductively isolated while in the midst of its parent population?

§This can occur if a genetic change produces a reproductive barrier between mutants and the parent population.

§Many plant species have originated from accidents during cell division that resulted in extra sets of chromosomes.

The process of instantaneous sympatric speciation: 

Polyploidy  

2x                         +                            4x

(haploid pollex (x1))                             (dipoloid ovule (2x))

=

(3x) triploid offspring: infertile, inviable

As a result, polyploidy generates immediate reproductive isolation and sympatric speciation

§Mutant species fail to produce fertile offspring with their parents resulting in reproductive isolation and speciation.

§In other words, sympatric speciation has occurred and there was no need for geographic isolation.

Sympatric speciation does not seem to be widespread in animals

but has been important in plant evolution.

Sympatric speciation

first discovered in the early 1900s by Dutch botanist Hugo de Vries.

de Vries identified a new species of primrose that arose through

sympatric speciation

The new species Hugo de Vries found was named Oenothera gigas and was a

tetraploid

The new species Hugo de Vries found was named Oenothera gigas and was a tetraploid

It could not interbreed with its parent species a diploid.

Most polyploid species arise from the

hybridzation of 2 parent species

hybridzation of 2 parent species mechanism

§accounts for many of the plant species we grow for food, including oats, potatoes, bananas, peanuts, barley, coffee and wheat.

What we call wheat is actually represented by

20 different species.

Humans began domesticating

wheat from wild grasses 11,000 years ago in the Middle East.

domesticating wheat

AA (domesticated Triticum gonococcus (14 chromosomes)) x BB (wild Triticum (14 chromosomes)) —→ (1.hybrization between two diploid wheats)—→ AB (Sterile hyrid (14 chromosome))

domesticating wheat

AA (domesticated Triticum gonococcus (14 chromosomes)) x BB (wild Triticum (14 chromosomes)) —→ (1.hybrization between two diploid wheats)—→ AB (Sterile hyrid (14 chromosome))

—>

(2.error in cell division followed by self-fertilization among gametes)

(AB becomes) AA BB (T. turgidum Emmer Wheat (28 chromosomes)) x DD (Wild T. turgidum (14 chromosomes))

domesticating wheat

AA (domesticated Triticum gonococcus (14 chromosomes)) x BB (wild Triticum (14 chromosomes)) —→ (1.hybrization between two diploid wheats)—→ AB (Sterile hyrid (14 chromosome))

(2.error in cell division followed by self-fertilization among gametes)

(AB becomes) AA BB (T. turgidum Emmer Wheat (28 chromosomes)) x DD (Wild T. turgidum (14 chromosomes)) —>

ABD(3. Hybidizaiton) 

domesticating wheat

AA (domesticated Triticum gonococcus (14 chromosomes)) x BB (wild Triticum (14 chromosomes)) —→ (1.hybrization between two diploid wheats)—→ AB (Sterile hyrid (14 chromosome))

(2.error in cell division followed by self-fertilization among gametes)

(AB becomes) AA BB (T. turgidum Emmer Wheat (28 chromosomes)) x DD (Wild T. turgidum (14 chromosomes)) —>

ABD(3. Hybridization)  —→

(4. Error in cell division followed by self-fertilization among gametes)  

(ABD becomes) AA BB DD (T. aestivum Bread wheat (42 chromosomes))

Two Models for the Tempo of Evolution

There are two models for the tempo of evolution:

Gradual vs Punctuated Equilibrium

Two Models for the Tempo of Evolution

Gradual model

states that species descended from a common ancestor diverge gradually in form as they acquire unique adaptations.

Two Models for the Tempo of Evolution

Punctuated equilibrium model

§ states that a new species changes quickly as it first branches off from a parent species, then there is little change for the rest of the species existence.

Two Models for the Tempo of Evolution

§But how can speciation, which may require several thousand years to occur, be called an abrupt or fast episode?

§Well, usually a successful species lasts for 5 million years, but most of its evolutionary changes occur during the first 50,000 years of its existence.

Two Models for the Tempo of Evolution

§Thus, 50,000 years over the entire span of evolutionary time does mark a “quick” change in speciation.

Age of the Earth: 4.5 billion years

Biologists use the term exaptation for

–for a structure that evolves in one context and later becomes adapted for other functions.

The Evolution of Biological Novelty

§How can we account for flight in birds?

–Biologists use the term exaptation for a structure that evolves in one context and later becomes adapted for other functions.

–In the case of birds, their ancestors had forelimbs that they used for movement.

–Once flight became an advantage, feathers and wings evolved to better fit the new function of these enlarged forelimbs.

The Evolution of Biological Novelty
§Birds are derived from a lineage of earthbound reptiles.

–These dinosaur ancestors were small, agile and bipedal.

The Evolution of Biological Novelty

Birds have lightweight skeletons with honeycombed bones.

This allows them to fly without weighing so much.

The Evolution of Biological Novelty

–Birds have lightweight skeletons with honeycombed bones. This allows them to fly without weighing so much.

The first flights may have been only glides or extended hops in an effort to

–pursue prey or escape from a predator.

The Evolution of Biological Novelty

–Bird ancestors with the ability to fly would have a selective feeding advantage over those animals that could not. Why?

§Can swoop down effortlessly at unsuspecting prey

§Can travel long distances

§Can hunt in new areas outside of local habitat

§Have faster speed from the air

§Can overcome physical obstacles

The Evolution of Biological Novelty

Archaeopteryx

Artist’s reconstruction of an extinct dinosaur

The Evolution of Biological Novelty

§Archaeopteryx.

§This animal lived near tropical lagoons in central Europe about 150 million years ago.

§Similar in size to a raven

§It is not considered an ancestor of modern birds.

The Evolution of Biological Novelty

§Archaeopteryx.

§This animal lived near tropical lagoons in central Europe about 150 million years ago.

§It is not considered an ancestor of modern birds.

§It probably represents an extinct side branch of the bird lineage.

The Evolution of Biological Novelty

§Archaeopteryx.

Bird-like features:

feathers, wings, wishbone

The Evolution of Biological Novelty

§Archaeopteryx.

Reptilian-like features:

teeth, claws, long bony tail, no beak present

The Evolution of Biological Novelty

Gradual evolutionary remodeling, such as flight in birds, probably involved

a large number of genetic changes in populations