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Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1. Allopatric Speciation 2. Sympatric Speciation

Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

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Page 1: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Fig. 24-5

(a) Allopatric speciation (b) Sympatric speciation

Speciation can occur in two ways:1. Allopatric

Speciation2. Sympatric

Speciation

Page 2: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

Allopatric (“Other Country”) Speciation

Page 3: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

The definition of barrier depends on the ability of a population to disperse

Separate populations may evolve independently through mutation, natural selection, and genetic drift

The Process of Allopatric Speciation

Page 4: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Fig. 24-6

A. harrisi A. leucurus

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

Page 5: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

In sympatric speciation, speciation takes place in geographically overlapping populations

Sympatric (“Same Country”) Speciation

Page 6: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division

Polyploidy is much more common in plants than in animals

Polyploidy

2n = 6 4n = 12

Failure of celldivision afterchromosomeduplication givesrise to tetraploidtissue.

2n

Gametesproducedare diploid..

4n

Offspring withtetraploidkaryotypes maybe viable andfertile.

Page 7: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

An allopolyploid is a species with multiple sets of chromosomes derived from different species

Allopolyploid

Species A2n = 6

Normalgameten = 3

Meioticerror

Species B2n = 4

Unreducedgametewith 4chromosomes

Hybridwith 7chromosomes

Unreducedgametewith 7chromosomes

Normalgameten = 3

Viable fertilehybrid(allopolyploid)2n = 10

Page 8: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Sympatric speciation can also result from the appearance of new ecological niches

For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees

Habitat Differentiation

Page 9: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Sexual selection can drive sympatric speciation

Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

Sexual Selection

EXPERIMENT

Normal lightMonochromatic

orange light

P.pundamilia

P. nyererei

Page 10: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

In allopatric speciation, geographic isolation restricts gene flow between populations

Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations

Even if contact is restored between populations, interbreeding is prevented

In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species

Sympatric speciation can result from polyploidy, natural selection, or sexual selection

Allopatric and Sympatric Speciation: A Review

Page 11: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

Adaptive Radiations

Page 12: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs

The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size

Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

Worldwide Adaptive Radiations

Page 13: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Adaptive radiations can occur when organisms colonize new environments with little competition

The Hawaiian Islands are one of the world’s great showcases of adaptive radiation

Regional Adaptive Radiations

Page 14: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Fig. 25-18

Close North American relative,the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearis

Dubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAI MAU

I

LANAI

Plants all descended from an ancestral tarweed that arrived on the islands about 5 million years ago

Page 15: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear

Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change

The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence - known as gradualism. Darwin supported the idea of slow gradual change.

Transition species found in the fossil record are a key component to gradualism.

Patterns Of Evolution

Page 16: Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation Speciation can occur in two ways: 1.Allopatric Speciation 2.Sympatric Speciation

Fig. 24-17

(a) Punctuated pattern

(b) Gradual pattern

Time