Chapter 24: The Origin of Species

Chapter 24: The Origin of Species

1. What is a species?- A population whose members can interbreed in nature and

produce viable, fertile offspring- aka….reproductive isolation

2. What kinds of barriers keep different species isolated so they cannot mate?- Figure 24.4- Pre–zygotic barriers – before mating &/or zygote is formed- Post–zygotic barriers – after zygote is formed

Figure 24.4 Reproductive Barriers

Prezygotic barriers impede mating or hinder fertilization if mating does occur

Individualsof differentspecies

Matingattempt

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION

(b)

(a)(c)

(d)

(e)

(f)

(g)

Viablefertile

offspring

Reducehybrid

viability

Reducehybridfertility

Hybridbreakdown

Fertilization

Gameticisolation

GAMETIC ISOLATION REDUCED HYBRID VIABILITY

REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

(h) (i)

(j)

(k)

(l)

(m)


1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?

- Allopatric speciation - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island

- Sympatric speciation- intrinsic factors such as chromosomal changes (plants) or

non-random mating alter gene flow

Figure 24.5 Two main modes of speciation

(a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population.

(b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation.



- Allopatric speciation – - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island- Adaptive radiation

- evolution of many diversely adapted species from a common ancestor

- Seen on islands- Sympatric speciation

- intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow

Figure 24.12 Adaptive radiation

Dubautia laxa

Dubautia waialealae

KAUA'I5.1

millionyears O'AHU

3.7millionyears

LANAI

MOLOKA'I

1.3 million years

MAUI

HAWAI'I0.4

millionyears

Argyroxiphium sandwicense

Dubautia scabraDubautia linearis

N







- ex. oats, cotton, tobacco, potatoes, wheat- Autopolyploidy

- An individual has more than 2 chromosome sets derived from a single species from an error in meiosis

Figure 24.8 Sympatric speciation by autopolyploidy in plants

2n = 64n = 12

2n

4n

Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.

Gametes produced by flowers on this branch will be diploid.

Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.







- Autopolyploidy - An individual has more than 2 chromosome sets derived from

a single species from an error in meiosis- Allopolyploidy

- 2 different species produce the polyploid hybrid

Figure 24.9 One mechanism for allopolyploid speciation in plants

Meiotic error;chromosomenumber notreduced from2n to n

Unreduced gametewith 4 chromosomes

Hybrid with7 chromosomes

Unreduced gametewith 7 chromosomes Viable fertile hybrid

(allopolyploid)

Normal gameten = 3

Normal gameten = 3

Species A 2n = 4

Species B 2n = 6

2n = 10


1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?4. What is the difference between gradualism & punctuated equlibrium?

Figure 24.13 Two models for the tempo of speciation

Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations.

Time

(a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.

(b)

Chapter 24: The Origin of Species

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