copyright © 2005 pearson education, inc. publishing as benjamin cummings chapter 24 the origin of...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Chapter 24 The Origin of Species

TOP 5


1. Ways at Classifying Species

• Biological species concept

– Population that has the potential to interbreed and produce viable, fertile offspring but unable to produce viable fertile offspring with members of other populations


Other Species Concepts

• Morphological

– Based on shape, size, etc.

• Ecological

– in terms ecological niche

• Phylogenetic

– in terms of unique genetic history


2. Biological Species Barriers

• Prezygotic barriers

– Impedes fertilization of ova

• Postzygotic barriers

– Prevents hybrid zygote from developing


• Prezygotic and postzygotic barriers

Figure 24.4

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)


(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.

Figure 24.5 A, B

Speciation can occur in 2 ways

– Allopatric

– Sympatric


3. Formation of Species: Allopatric

• Allopatric speciation

– Population is divided into 2 or more geographically isolated subpopulations


Figure 24.6

A. harrisi A. leucurus

• Geographic separation

evolutionary change during the period of separation



– Reproductive isolation

Figure 24.7

Initial population of fruit flies(Drosphila

Pseudoobscura)

Some fliesraised on

starch medium

Some fliesraised on

maltose mediumMating experimentsafter several generations

EXPERIMENT Diane Dodd, of Yale University, divided a fruit-fly population, raising some populations on a starch medium and others on a maltose medium. After many generations, natural selection resulted in divergent evolution: Populations raised on starch digested starch more efficiently, while those raised on maltose digested maltose more efficiently. Dodd then put flies from the same or different populations in mating cages and measured mating frequencies.


3. Formation of Species: Sympatric

• Sympatric speciation

– Geographically overlapping populations


• Polyploidy

– Extra sets of chromosomes f/ accidents during cell division


• Autopolyploid

– More than two chromosome sets, f/ same species

Figure 24.8

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.


• Allopolyploid

– Multiple sets of chromosomes derived from different species

Figure 24.9

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


Goat’s Beard

• Illustration of an Allopolyploid


Sexual Selection

• Cichlid fish

– Sympatric speciation f/ nonrandom mating due to sexual selection

Figure 24.10

Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orangelight, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank.

EXPERIMENT

P. nyererei

Normal lightMonochromatic

orange light

P. pundamilia

Under normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile.

RESULTS

The researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently.

CONCLUSION



– Speciation due to geographic isolation

• Sympatric speciation

– Barrier isolates a subset of a population without geographic separation


5. Adaptive Radiation

• Adaptive radiation

– Evolution of diversely adapted species from a common ancestor upon introduction to new environment

Figure 24.11


• Hawaiian archipelago

– Showcase of adaptive radiation

Figure 24.12

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 scabra Dubautia linearis

N

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