Ch 24 2

(1)

PowerPoint Lectures for

Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 24

(2)

The Biological Species Concept

•

The biological species concept

(3)

Reproductive Isolation

•

Reproductive isolation: the existence of

biological factors that impede members of two

species from producing viable, fertile hybrids

1.

Prezygotic barriers (BEFORE sperm meets egg)

–

Impede mating between species or hinder the

fertilization of ova if members of different species

attempt to mate

2.

Postzygotic barriers (AFTER sperm meets egg)

–

Often prevent the hybrid zygote from developing into a

(4)

End G thurs

•

Prezygotic barriers

Prezygotic barriers impede mating or hinder fertilization if mating does occur

Individuals

of different

species

Mating attempt

Habitat

isolation

Temporal

isolation

Behavioral

isolation

Mechanical

isolation

(5)

Postzygotic Barriers

Viable fertile offspring

Reduce

hybrid

viability

Reduce

hybrid

fertility

Hybrid

breakdown

Fertilization

Gametic

isolation

GAMETIC ISOLATION

REDUCED HYBRID

VIABILITY

REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

(h)

(i)

(j)

(k)

(l)

(6)

(7)

Limitations of the Biological Species Concept

•

The biological species concept cannot be

applied to

–

Asexual organisms

–

Fossils

–

Organisms about which little is known

(8)

(9)

Other Definitions of Species: UNITING features…

1.

The

morphological

species concept

–

Characterizes a species in terms of its body shape, size,

and other structural features

2.

The

ecological

species concept

–

Views a species in terms of its ecological niche

3.

The

phylogenetic

species concept

(10)

Allopatric and sympatric speciation

•

Concept 24.2: Speciation can take place with

or without geographic separation

•

Speciation can occur in two ways

–

Allopatric

speciation: Gene flow is interrupted

or reduced when a population is divided into

two or more geographically isolated

subpopulations

–

Sympatric

speciation: Speciation takes place

(11)

(12)

Mechanisms of sympatric speciation: Polyploidy

•

Autopolyploid: an individual that has more than

two chromosome sets, all derived from a single

species

(13)

•

Allopolyploid: a species with multiple sets of

chromosomes derived from different species

Figure 24.9

Meiotic error;

chromosome

number not

reduced from

2

n

to

n

Unreduced gamete

with 4 chromosomes

Hybrid with

7 chromosomes

Unreduced gamete

with 7 chromosomes

Viable fertile hybrid

(allopolyploid)

Normal gamete

n

= 3

Normal gamete

n

= 3

Species A

2

n

= 4

Species B

2

n

= 6

2

n

= 10

Usually

infertile

(14)

End G mon

•

Wheat is weird….

(15)

Evidence for sympatric speciation: Habitat differentiation

•

Hawthorn and apple maggot flies

(16)

Evidence for sympatric speciation: sexual selection

–

Sympatric speciation has resulted from

nonrandom mating due to sexual selection

Pundamilia pundamilia

and

P. nyererei

together under natural

light- two species are noticeably different in coloration and under

amonochromatic orange lamp- the two species appear identical in

color.

EXPERIMENT

P. nyererei

Normal light

Monochromatic

orange light

P. pundamilia

(17)

Hybrid Zones end a mon

•

Hybrid zone: a region where members of

different species meet and mate, producing at

least some offspring of mixed ancestry

(18)

Fate of a hybrid zone

•

Hybrids are often a “dead end”

–

Reduced fitness

•

Hybrid may become its own species:

goatsbeard plant

•

Reinforcement of reproductive barriers, limiting

future hybrids

(19)

Reinforcement of reproductive barriers

•

If hybrids are less fit, natural selection should

(20)

Fusion of species

•

Murky waters caused by pollution seem to

(21)

How fast is speciation?

•

Well, both fast and slow of course.

•

Patterns in the fossil record:

–

Punctuated equilibria: stasis punctuated by

seemingly rapid changes in the fossil record

–

Other species show gradual change in the

fossil record

(22)

•

The punctuated equilibrium model

(23)

•

Species concepts

•

Isolating mechanisms

•

Paths to speciation

•

Hybrid zones

(24)

•

Who set the stage for Darwin?

•

Summarize Darwin’s big idea

•

What is modern evidence for natural selection?

•

What conditions must be met for allele frequencies to remain constant?

•

What is the Hardy Weinberg equation?

•

How do allele frequencies change? Name three ways..

•

Name at least four types of selection

•

How is diversity preserved?

http://www.youtube.com/watch?v=1NAKg46s1DA