how did this flightless bird come to live on the isolated

Food for thoughtHow did this flightless bird come to live on the isolated

Galápagos Islands?

EVOLUTION & SPECIATION

What species

is this?

Equus asinus× Equus caballusMules and hinnies have 63 chromosomes,

a mixture of the horse's 64 and the donkey's 62

How did this flightless bird come to live on the isolated Galápagos Islands?

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Animation: Macroevolution Right-click slide / select “Play”

VOCABULARY REVIEW

• EVOLUTION – CHANGE OVER TIME

• NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE.

• A.K.A. “SURVIVAL OF THE FITTEST”

NEW VOCABULARY

• POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED

• GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION

Gene Pool

Combined genetic info. of all members

Allele frequency is # of times alleles occur

Variation in Populations

2 processes can

lead to this:

Mutations -

change in DNA

sequence

Gene Shuffling –

from sexual

reproduction

Genetic Drift changes populations…….

• Random change in allele frequency causes an allele to become common

• Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population

• Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

• Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)

• Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

Sexual selection• Sexual dimorphism:

secondary sex characteristic distinction

• Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

Evolution of Populations

Occurs when there is a change in relative frequency of alleles

Generation 1: 1.00 not resistant0.00 resistant

Resistance to antibacterial soap

How natural selection works

Resistance to antibacterial soap

Generation 1: 1.00 not resistant0.00 resistant

How natural selection works

Resistance to antibacterial soap

mutation!

Generation 1: 1.00 not resistant0.00 resistant

Generation 2: 0.96 not resistant0.04 resistant

How natural selection works

Resistance to antibacterial soap

Generation 1: 1.00 not resistant0.00 resistant

Generation 2: 0.96 not resistant0.04 resistant

Generation 3: 0.76 not resistant0.24 resistant

How natural selection works

Resistance to antibacterial soap

Generation 1: 1.00 not resistant0.00 resistant

Generation 2: 0.96 not resistant0.04 resistant

Generation 3: 0.76 not resistant0.24 resistant

Generation 4: 0.12 not resistant0.88 resistant

How natural selection works

Phenotype Expression

• Depends on how many genes control that trait

Single-Gene vs. Polygenic Traits

Single-Gene:

2 Distinct Phenotypes

Polygenic:

Many Phenotypes

(EG: tongue rolling)

Allele Frequencies

Natural Selection Genetic Drift

Single Gene

Traits

Polygenic

Traits

Directional

Selection

Stabilizing Selection

Disruptive Selection

Natural Selection on Polygenic Traits

• Shifts to

middle range

• Shifts to

2 extremes

• Shifts to

1 extreme

Conditions needed for Genetic Equilibrium

SPECIATION

• THE FORMATION OF NEW SPECIES

• AS NEW SPECIES EVOVLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED

• REPRODUCTIVE ISOLATION – the existence of a barrier that prevents 2 populations from breeding…

• MEMEBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING.

Scale of evolution:

• Microevolution consists of changes in allele frequency in a population over time

• Macroevolution refers to broad patterns of evolutionary change above the species level

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Process of species change

What defines a species?

The biological species concept emphasizes reproductive isolation

• Biological Species Concept (one way to divide species):

• A species is a group of populations whose members can breed and produce viable, fertile offspring• Ability to mate = formation of a species

• Gene flow between populations holds together the phenotype of a population (ongoing exchange of alleles)

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It’s all about ability to breed

(a) Similarity between different species

(b) Diversity within a species

Reproductive Isolation is the driving force behind Speciation

• A new species will form when reproductive isolationoccurs

• Absence of gene flow

• Reproductive Isolation:• The existence of biological factors (barriers) that prevent two

individuals of a species from mating and producing viable and fertile offspring

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Figure 24.3_b

Prezygotic barriers

Habitat

Isolation

Temporal

Isolation

Behavioral

Isolation

Mechanical

Isolation

Gametic

Isolation

Individuals of

differentspecies

MATINGATTEMPT

FERTILIZATION

(a) (c) (e) (f)

(b)

(g)

(d)

Reduced Hybrid

Viability

Reduced Hybrid

Fertility

Hybrid

Breakdown

FERTILIZATION

VIABLE,FERTILE

OFFSPRING

Postzygotic barriers

(k)

(h) (i)

(j)

(l)

Figure 24.3_c

Limitations of the Biological Species Concept

• The biological species concept (BSC) cannot be applied to fossils or asexual organisms (including all prokaryotes)

• The biological species concept emphasizes absence of gene flow

However, gene flow can occur between distinct species

• HYBRIDS: For example, grizzly bears and polar bears can mate to produce “grolar bears”

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Figure 24.4Grizzly bear (U. arctos)

Polar bear (U. maritimus)

Hybrid “grolar bear”

Other Definitions of Species2. morphological species concept:

• A species is characterized by its body shape

• It applies to sexual and asexual species but relies on subjective criteria

3. ecological species concept:• A species is characterized by its ecological niche

• It applies to sexual and asexual species and emphasizes the role of disruptive selection

4. phylogenetic species concept:• A species is the smallest group of individuals that share a

common ancestor

• It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

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Bellwork:

Concept 24.2: Speciation can take place with or without geographic separation

• Speciation can occur in two ways:• Allopatric speciation• Sympatric speciation

• What do the route words mean?

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Figure 24.5

(a) (b)Allopatric speciation.

A population forms a

new species while

geographically isolated

from its parent population.

Sympatric speciation.

A subset of a population

forms a new species

without geographic

separation.

Allopatric (“Other Country”) Speciation

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

• For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland

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The Process of Allopatric Speciation

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

• For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen

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A. harrisii A. leucurus

ALLOPATRIC SPECIATION

A. formosus

Atlantic Ocean

A. nuttingi

Isthmus of Panama

Pacific Ocean

A. panamensis A. millsae

Sympatric (“Same Country”) Speciation

• In sympatric speciation, speciation takes place in geographically overlapping populations

• In a sympatric speciation, various factors can limit gene flow:

• Polyploidy• Habitat differentiation• Sexual selection

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Reproductive Isolation Mechanism• BEHAVIORAL ISOLATION- CAPABLE OF

BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS)

• GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL)

• TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.

Table 23.1a

Tigon

Result of male tiger and female lion mating incaptivity. Offspring are infertile.

Separated both geographically and ecologically.

Liger

Result of male lion and female tiger mating in captivity. Offspring are infertile.

Table 23.1b

Fig. 23.6

Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.

These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

Hawaiian Honeycreepers

FOUNDER SPECIES

An example of adaptive radiation –these species all diverged from acommon ancestor (founder species)

SPECIATION IN DARWIN’SFINCHES

• SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY:

- FOUNDING OF A NEW POPULATION,

- GEOGRAPHIC ISOLATION which led to -- REPRODUCTIVE ISOLATION and

CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.