Defining Species - PowerPoint Presentation

Slide1
Slide2

Defining SpeciesSlide3

I can…

Distinguish between microevolution and speciation.

Compare the definitions, advantages, and disadvantages of the different species concepts.

Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations of closely related species from interbreeding.Slide4

14.1 The origin of species is the source of

biological diversity

Microevolution is the change in the gene pool of a population from one generation to the next.

Speciation

is the process by which one species splits into two or more species.Each time speciation occurs, the diversity of life increases.Slide5

14.2 There are several ways to define a species

The

biological species concept

defines a species as a group of populations whose members have the potential to interbreed in nature and produce fertile offspring.

Thus, members of a biological species are united by being reproductively compatible. Slide6

14.2 There are several ways to define a species

Reproductive isolation

prevents genetic exchange (gene flow) and maintains a boundary between species.

Hybrids:

clearly distinct species that do occasionally interbreed.

An example is the grizzly bear and the polar bear, whose hybrid offspring have been called “grolar bears.”Slide7

14.2 There are several ways to define a species

There are other instances in which applying the biological species concept is problematic.

There is no way to determine whether organisms that are now known only through fossils were once able to interbreed.

Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually.

Therefore, alternate species concepts can be useful.Slide8

14.2 There are several ways to define a species

The

morphological species concept

classifies organisms based on observable physical traits and can be applied to asexual organisms and fossils.

The ecological species concept

defines a species by its ecological niche and focuses on unique adaptations to particular roles in a biological community.

The

phylogenetic species concept

defines a species as the smallest group of individuals that share a common ancestor and thus form one branch of the tree of life.Slide9

14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate

Reproductive barriers

serve to isolate the gene pools of species and prevent interbreeding.

Reproductive barriers are categorized as

Prezygotic: before zygotes formPostzygotic

:

after

zygotes formSlide10

14.3 Reproductive barriers keep species separate

Five types of

prezygotic barriers

prevent mating or fertilization between species.Slide11

Figure 14.3-1

Habitat isolation

(lack of opportunities to encounter each other)

The garter snake

Thamnophis

atratus

lives mainly in water.

The garter snake

Thamnophis sirtalis

lives on land.Slide12

Figure 14.3-2

Temporal isolation

(breeding at different times or seasons)

The eastern spotted skunk

(

Spilogale putorius

) breeds in

late winter.

The western spotted skunk

(

Spilogale gracilis

) breeds in

the fall.Slide13

14.3 Reproductive barriers keep species separate

Blue footed booby courtship ritual:

http://www.arkive.org/blue-footed-booby/sula-nebouxii/video-09a.html

Slide14

Figure 14.3-4

Mechanical isolation

(physical incompatibility of reproductive parts)

Heliconia pogonantha

is

pollinated by hummingbirds

with long, curved bills.

Heliconia latispatha

is pollinated

by hummingbirds with short,

straight bills.Slide15

Figure 14.3-5

Gametic isolation

(molecular incompatibility of eggs and sperm

or pollen and stigma)

Purple sea urchin

(

Strongylocentrotus

purpuratus

)

Red sea urchin

(

Strongylocentrotus

franciscanus

)Slide16

14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate

Three types of

postzygotic barriers

operate after hybrid zygotes have formed.Slide17

Figure 14.3-6

Reduced hybrid viability

(hybrid development or survival impaired

by interaction of parental genes)

Some salamander species can hybridize,

but their offspring do not develop fully or

are frail and will not survive long enough

to reproduce.Slide18

Figure 14.3-7

Reduced hybrid fertility

(vigorous hybrids that cannot

produce viable offspring)

A mule is the sterile hybrid

offspring of a horse and a donkey.Slide19

Figure 14.3-8

Hybrid breakdown

(viable and fertile hybrids with feeble

or sterile offspring)

The rice hybrids on the left and right

are fertile, but plants of the next

generation (middle) are sterile.Slide20

Mechanisms of SpeciationSlide21

I can…

Explain how geologic processes can fragment populations and lead to speciation.

Explain how reproductive barriers might evolve in isolated populations of organisms.

Explain how sympatric speciation can occur.

Describe the circumstances that led to the adaptive radiation of the Galápagos finches.Slide22

14.4 In allopatric speciation, geographic isolation leads to speciation

A key event in the origin of a new species is the separation of a population from other populations of the same species.

With its gene pool isolated, the splinter population can follow its own evolutionary course.

Changes in allele frequencies caused by natural selection, genetic drift, and mutation will not be diluted by alleles entering from other populations (gene flow). Slide23

14.4 In allopatric speciation, geographic isolation leads to speciation

In

allopatric speciation

, the initial block to gene flow may come from a

geographic barrier that isolates a population.Slide24

14.4 In allopatric speciation, geographic isolation leads to speciation

Several geologic processes can isolate populations.

A mountain range may emerge and gradually split a population of organisms that can inhabit only lowlands.

A large lake may subside until there are several smaller lakes, isolating certain fish populations.

Continents themselves can split and move apart. How large must a geographic barrier be to keep allopatric populations apart?

depends on the ability of the organisms to moveSlide25

14.5 Reproductive barriers can evolve as populations diverge

How do reproductive barriers arise?

As a result of natural selection acting on preexisting variations (or as a result of genetic drift or mutation), a population’s traits may change in ways that also establish reproductive barriers.

http://www.hhmi.org/biointeractive/anole-lizards-example-speciation

(3 min)Slide26

14.6 Sympatric speciation takes place without geographic isolation

Sympatric speciation

occurs when a new species arises within the

same geographic area

as its parent species.How can reproductive isolation develop when members of sympatric populations remain in contact with each other?Gene flow between populations may be reduced byPolyploidy (usually plants),

habitat differentiation or sexual selection (usually animals) .Slide27

14.6 Sympatric speciation takes place without geographic isolation

Many plant species have originated from sympatric speciation that occurs when accidents during cell division result in extra sets of chromosomes.

New species formed in this way are

polyploid

, in that their cells have more than two complete sets of chromosomes.Slide28

14.6 Sympatric speciation takes place without geographic isolation

Sympatric speciation can result from polyploidy

within a species (by self-fertilization)

between two species (by hybridization).Slide29

14.7 EVOLUTION CONNECTION: The origin of most plant species can be traced to polyploid speciation

Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation.

Hybridization between two species accounts for most of these species, perhaps because of the adaptive advantage of the diverse genes a hybrid inherits from different parental species. Slide30

14.7 The origin of most plant species can be traced to polyploid speciation

Polyploid plants include

cotton,

oats,

potatoes,bananas,

peanuts,

barley,

plums,

apples,

sugarcane,

coffee, and

wheat.Slide31

14.8 Isolated islands are often showcases of speciation

Isolated island chains are often inhabited by unique collections of species.

Islands that have physically diverse habitats and that are far enough apart to permit populations to evolve in isolation but close enough to allow occasional dispersions to occur are often the sites of multiple speciation events.

The evolution of many diverse species from a common ancestor is known as

adaptive radiation.Slide32

14.8 Isolated islands are often showcases of speciation

The Galápagos Islands currently have 14 species of closely related finches.

These birds

differ in their feeding habits and their beaks, specialized for what they eat, and arose through adaptive radiation.

http://www.hhmi.org/biointeractive/origin-species-beak-finch

(16 min)Slide33
Slide34

I can…

1. Explain how new species of fish have evolved in Lake Victoria.

2. Explain how hybrid zones are useful in the study of reproductive isolation.

3. Compare the gradual model and the punctuated equilibrium model of evolution.Slide35

14.9 SCIENTIFIC THINKING: Lake Victoria is a living laboratory for studying speciation

Biologists are still studying the process of speciation.

Cichlid fish populations

They come in all colors of the rainbow.

Live in the large lakes of East Africa with more than a thousand species of cichlids in less than 100,000 years.In the largest of these lakes, Lake Victoria, roughly 500 species evolved in about 15,000 years.Slide36

14.9 SCIENTIFIC THINKING: Lake Victoria is a living laboratory for studying speciation

In Lake Victoria, there are pairs of closely related cichlid species that differ in color but nothing else.

Breeding males of

Pundamilia nyererei

have a bright red back and dorsal fin.Breeding males of Pundamilia pundamilia males are metallic blue-gray.Slide37

14.9 Lake Victoria is a living laboratory for studying speciation

Pundamilia

females prefer brightly colored males.

Mate-choice experiments performed in the laboratory showed that P. nyererei females prefer red males over blue males, P. pundamilia

females prefer blue males over red males,

the vision of

P. nyererei

females is more sensitive to red light than blue light, and

the vision of

P. pundamilia

females is more sensitive to blue light than red light.

Researchers also demonstrated that this color sensitivity is heritable.Slide38

14.9 Lake Victoria is a living laboratory for studying speciation

As light travels through water, suspended particles selectively absorb and scatter the shorter (blue) wavelengths, so light becomes increasingly red with increasing depth.

Thus, in deeper waters,

P. nyererei

males are pleasingly apparent to females with red-sensitive vision but virtually invisible to P. pundamilia females.

When biologists sampled cichlid populations in Lake Victoria, they found that

P. nyererei

breeds in deep water, while

P. pundamilia

inhabits shallower habitats where the blue males shine brightly.

As a consequence of their mating behavior, the two species encounter different environments that may result in further divergence.Slide39

14.10 Hybrid zones provide opportunities to study reproductive isolation

What happens when separated populations of closely related species come back into contact with each other?

Biologists try to answer such questions by studying

hybrid zones

, regions in which members of different species meet and mate to produce at least some hybrid offspring.Slide40

14.10 Hybrid zones provide opportunities to study reproductive isolation

Species may interbreed in a hybrid zone.

There are 3 possible hybrid zone outcomes

Reinforcement:

when reproductive barriers are strengthened and keep species separate.Fusion: when reproductive barriers are weakened or eliminated and speciation is reversed.

Stability:

when a few hybrids continue to be produced.Slide41

When hybrid offspring are less fit than members of both parent species,

natural selection to strengthen, or

reinforce

, reproductive barriers

barriers between species should be stronger where the species overlap (sympatric).The closely related collared flycatcher and pied flycatcher are an example of reinforcement.

 Slide42

14.10 Hybrid zones provide opportunities to study reproductive isolation

Fusion 

Reproductive barriers between species are not strong and the species come into contact in a hybrid zone.

So much gene flow may occur that the speciation process reverses, causing the two hybridizing species to fuse into one.

Such a situation has been occurring among the cichlid species in Lake Victoria.Slide43

14.10 Hybrid zones provide opportunities to study reproductive isolation

Pollution caused by development along the shores of Lake Victoria has turned the water murky.

What happens when

P. nyererei or P. pundamilia females can’t tell red males from blue males?

The behavioral barrier crumbles.

Many viable hybrid offspring are produced by interbreeding.

The once isolated gene pools of the parent species are combining, with two species fusing into a single hybrid species.Slide44

14.10 Hybrid zones provide opportunities to study reproductive isolation

Stability

Many hybrid zones are fairly stable and hybrids continue to be produced.

Example: the islands inhabited by two finch species occasionally interbreed.Slide45

Speciation of California Salamanders and Hybrid Zones

https://www.youtube.com/watch?v=aDIQFQOCGaI

(3.5 min)

Is this an example of reinforcement, fusion, or stability? Slide46

14.11 Speciation can occur rapidly or slowly

There are two models for the tempo of speciation.

The

punctuated equilibria:

long periods of little apparent morphological change (equilibria) interrupted (punctuated) by relatively brief periods of sudden change.

Other species appear to have evolved more

gradually

. Slide47

Figure 14.11

Punctuated pattern

Gradual pattern

TimeSlide48

Crash Course: Speciation

https://www.youtube.com/watch?v=2oKlKmrbLoU

10:25 minSlide49
Slide50

Figure 14.UN05

Zygote

Gametes

Viable,

fertile

offspring

Prezygotic

barriers

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

Gametic

isolation

Postzygotic

barriers

Reduced hybrid

viability

Reduced hybrid

fertility

Hybrid breakdownSlide51

Figure 14.UN06

Original population

a.

b. Slide52

Figure 14.UN07

Species

reproductive

barriers

a few

hybrids

continue to

be produced

species

separate

speciation is

reversed

a.

b.

c.

d.

e.

f.

may interbreed

in a

outcome may be

when

are

keeps

and

when

when

are