SPEC

I.

WHAT IS A SPECIES?

A.

EMPHASIZE PROCESS

1. BIOLOGICAL SPECIES CONCEPT

2. RECOGNITION SPECIES CONCEPT

B. EMPHASIZES PATTERNS

1. PHYLOGENETIC SPECIES CONCEPT

SPECIATION:

1.

HOW DOES ONE GENE POOL SPLIT INTO TWO?

2.

WHAT MAINTAINS SEPARATE GENE POOLS?

II. REPRODUCTIVE ISOLATING MECHANSIMS

A.

EXTRINSIC BARRIERS

1. GEOGRAPHIC

2. ECOLOGICAL

II. REPRODUCTIVE ISOLATING MECHANSIMS

A.

EXTRINSIC BARRIERS

B. INTRINSIC BARRIERS

1. PREZYGOTIC

-PREMATING

-LOCK AND KEY

-GAMETIC INCOMPATIBILITY

2. POSTZYGOTIC

-ZYGOTE INVIABILITY

-HYBRID DISADVANTAGE

-HYBRID DEATH OR STERILITY

Is reproductive isolation a direct or by-product of evolution?

IV. GEOGRAPHY OF

SPECIATION

A.

ALLOPATRY

B.

SYMPATRY

C.

PARAPATRY

A

A

B

A B

B

V. MODELS OF SPECIATION

1.

ALLOPATRY

A. DIVERGENT NATURAL SELECTION

-GEOGRAPHICALLY ISOLATED POPULATIONS DIVERGE IN

RESPONSE TO NOVEL ENVIRONMENT OR NEW SELECTIVE

PRESSURES

-ADAPTATION TO NEW ENVIRONMENT RESULTS IN REPRODUCTIVE

ISOLATION


1.

ALLOPATRY


• POPULATIONS (OR SPECIES)

DIVERGE IN RESPONSE TO

FOOD RESOURCES

• CHANGE IN BILL AND HEAD

MORPHOLOGY

PREDICTION: CHANGES IN

MORPHOLOGY RESULTS IN

REPRODUCTIVE ISOLATION


1.

ALLOPATRY


• ARE DIFFERENCES IN HEAD MORPHOLOGY USED FOR CONSPECIFIC

RECOGNITION?

SUBJECT MODEL NO. APPROACH NO. PECKS

2.8 ± 0.4

7.9 ± 4.7

G. scandens

2.0 ± 0.4

1.6 ± 0.9

different

Ratcliffe and Grant 1983


1.

ALLOPATRY



RECOGNITION?

SUBJECT HEAD MODEL NO. APPROACH NO. PECKS

3.6 ± 0.8

5.4 ± 1.9

G. scandens G. scandens BODY

G. scandens BODY

2.0 ± 0.4

2.5 ± 0.8

different


1.

ALLOPATRY



RECOGNITION?


2.5 ± 0.6

0.6 ± 0.4

G. scandens G. fortis BODY

G. scandens BODY

2.9 ± 1.1

2.1 ± 1.9

not different


1.

ALLOPATRY



RECOGNITION?


2.6 ± 0.6

2.7 ± 1.3

G. scandens G. fortis BODY

1.6 ± 0.2

3.1 ± 1.6

G. scandens BODY not different

STUDY SUGGESTS THAT BOTH HEAD AND BODY SIZE ARE IMPORTANT


1.

ALLOPATRY


DO CHANGES IN HEAD MORPHOLOGY INFLUENCE OTHER TRAITS?

Podos et al. 2004


1.

ALLOPATRY


CHANGES IN HEAD

MORPHOLOGY INFLUENCE

SONG PRODUCTION interspecific variation intraspecific variation: G. fortis

Podos 2001


1.

ALLOPATRY


SONG IMPORTANT IN CONSPECIFIC RECOGNITION

SONG TYPE

G. scandens

NUMBER OF NEIGHBORS ATTRACTED

23

0

G. fortis

4

25

Ratcliffe and Grant 1983


1.

ALLOPATRY


OTHER STUDIES SHOWING NS AND SPECIATION

Three-spined stickleback feeding

Pea Aphids

Walking sticks

Heliconius butterflies host plant host plant warning coloration


1.

ALLOPATRY

B. DIVERGENT SEXUAL SELECTION

DIFFERENCES IN MATE CHOICE PROCESS RESULTS IN

DIFFERENCES IN SIGNALS USED IN COMMUNICATION

-CHANGES IN SIGNALS RESULTS IN REPRODUCTIVE ISOLATION

(PREMATING)

PREDICTIONS: DIVERGENCE ONLY IN SECONDARY SEXUAL

CHARACTERS

PREDICTIONS: DIVERGENT CHARACTERS USED IN CONSPECIFIC

RECOGNITION


1.

ALLOPATRY


PREDICTION 1: “SPECIES” SHOULD ONLY

DIFFER IN SECONDARY SEXUAL

CHARACTERS

Gryllus spp . crickets by Gray and Cade (2000)

-CRYPTIC SPECIES: INDISTINGUISHABLE

MORPHOLOGICALLY

-ONLY DIFFER IN MALE SEX TRAIT: CALL RATE

Gryllus texensis

Gryllus rubens


1.

ALLOPATRY


PREDICTION 1: “SPECIES” SHOULD ONLY DIFFER IN

SECONDARY SEXUAL CHARACTERS


-CRYPTIC SPECIES: INDISTINGUISHABLE MORPHOLOGICALLY

-ONLY DIFFER IN MALE SEX TRAIT: CALL RATE


1.

ALLOPATRY


PREDICTION 2: FEMALES SHOULD USE DIVERGENT

TRAITS IN RECOGNIZING CONSPECIFICS



1.

ALLOPATRY


OTHER STUDIES

TAXA

HAWAIIAN CRICKETS

BOWERBIRDS

JUMPING SPIDERS

HAWAIIAN Drosophila

TRAIT

SONG

BOWER STRUCTURE

MALE COLORATION

HEAD SIZE (COURTSHIP)


1.

ALLOPATRY

2.

SYMPATRY


PREDICTIONS: POPULATIONS DIVERGE IN SYMPATRY

PREDICTIONS: POPULATIONS DIVERGE IN RESPONSE TO SPECIFIC

ECOLOGICAL FACTORS

PREDICTION: HABITAT SPECIFIC MATING RESULTS IN



1.

ALLOPATRY

2.

SYMPATRY


POPULATIONS DIVERGE IN RESPONSE TO SPECIFIC

ENVIRONMENTAL FACTORS DESPITE NOT BEING

GEOGRAPHICALLY ISOLATED

-PRIME CANDIDATES: INSECT – HOST PLANT

-NEED POLYMORPHISM AND DISRUPTIVE SELECTION

-VERY STRICT MODEL BECAUSE GENE FLOW CAN PREVENT

SPECIALIZATION


1.

ALLOPATRY

2.

SYMPATRY


Example(?): apple maggot fly Rhagoletis pomonella

-work by many started by Walsh (late 1800’s) and Bush.


1.

ALLOPATRY

2.

SYMPATRY


Apple maggot fly Rhagoletis pomonella

-MID 1800s, SOME SHIFTED TO DOMESTIC APPLES

-NEW HOST RACES

IS THIS AN EXAMPLE OF SYMPATRIC SPECIATION?


1.

ALLOPATRY

2.

SYMPATRY


Example(?):

Apple maggot fly Rhagoletis pomonella

PREDICTION1: POPULATIONS DIVERGE IN SYMPATRY

YES, RECORDS SHOW SHIFT TO NEW HOST PLANTS AROUND MID

1800


1.

ALLOPATRY

2.

SYMPATRY


Example(?):

Apple maggot fly Rhagoletis pomonella

PREDICTION 2: POPULATIONS DIVERGE IN RESPONSE TO SPECIFIC

ECOLOGICAL FACTORS

-SHIFT FROM HAWTHORNE TO APPLE

ADVANTAGE?

RECIPROCAL TRANSPLANTS OF EGGS (Prokopy and colleagues 1988):

LARVAL SURVIVORSHIP

APPLE LARVAE = HAWTHORN LARVAE IN HAWTHORN

APPLE LARVAE = HAWTHORN LARVAE IN APPLE (BOTH DID

POORLY!)


1.

ALLOPATRY

2.

SYMPATRY


Example(?): Apple maggot fly Rhagoletis pomonella

PREDICTION 2: POPULATIONS DIVERGE IN RESPONSE TO SPECIFIC

ECOLOGICAL FACTORS

-SHIFT FROM HAWTHORN TO APPLE

ADVANTAGE?

-ENEMY FREE SPACE

-TIMING OF EMERGENCE FROM THE GROUND

APPLE PEAKS 3 WEEKS EARLIER THAN HAWTHORN

APPLE Rhagoletis LARVAE LEAVE APPLES 16 DAYS BEFORE

HAWTHORN

HAVE TO STAY IN DIAPAUSE LONGER OR WILL ECLOSE IN

WINTER – SO APPLE FLIES DEVELOP SLOWER THAN

HAWTHORN FLIES


1.

ALLOPATRY

2.

SYMPATRY


Example(?): Apple maggot fly Rhagoletis pomonella

PREDICTION 3: HABITAT SPECIFIC MATING RESULTS IN


FIELD EXPERIMENTS: MATE AND GROW EXCLUSIVELY IN HOST

PLANT

GENETICS:

SIX LOCI SHOW ASSOCIATION WITH HOST RACE

BUT MANY OTHERS DO NOT

-MARK RECAPTURE

STRONG FIDELITY, BUT 6% MIGRATION


1.

ALLOPATRY

2.

SYMPATRY


OTHER STUDIES:

NONE....


2. SYMPATRY


DIFFERENCES IN MATE CHOICE PROCESS RESULTS IN

DIFFERENCES IN SIGNALS USED IN COMMUNICATION

-CHANGES IN SIGNALS RESULTS IN PREZYGOTIC ISOLATION

(PREMATING)

PREDICTIONS: POPULATIONS DIVERGE IN SYMPATRY

PREDICTIONS: DIVERGENCE ONLY IN SECONDARY SEXUAL

CHARACTERS

PREDICTIONS: DIVERGENT CHARACTERS USED IN CONSPECIFIC

RECOGNITION


2. SYMPATRY


Lake Victoria cichlid: Haplochromis nyererei by Seehausen and van Alphen 1998

PREDICTION 1: POPULATIONS DIVERGE IN SYMPATRY

-PHYLOGENY: MONOPHYLETIC GROUP IN A SINGLE LAKE

-LAKE IS RECENT AND SMALL

PREDICTIONS 2: DIVERGE ONLY IN SECONDARY SEXUAL

CHARACTERS

-SOME DIVERGENCE IN BODY SIZE

-MOST STRIKING IN COLOR


2. SYMPATRY


Haplochromis nyererei by Seehausen and van Alphen 1998

PREDICTION 3: FEMALES USE COLOR TO FIND CONSPECIFIC

Normal Light

0.3

0.3

0.2

0.2

0.1

0

0.3

0.2

0.1

0

0.1

0

0.3

0.2

0.1

0


2. SYMPATRY


Haplochromis nyererei by Seehausen and van Alphen 1998

PREDICTION 3: FEMALES USE COLOR TO FIND CONSPECIFIC

0.3

Mono Light

0.3

0.2

0.2

0.1

0

0.1

0.3

0

0.2

0.1

0

0.1

0

0.3

0.2


2. SYMPATRY


OTHER STUDIES

Lake Malawi Cichlids Coloration


3. REINFORCEMENT

THREE STEPS:

DIVERGE OR CHANGE IN ALLOPATRY

ESTABLISH SECONDARY CONTACT

SELECTION AGAINST HYBRIDIZATION RESULTS IN

EXAGGERATION OF SEX TRAITS TO FACILITATE CONSPECIFIC

RECOGNITION

PREDICTIONS: SECONDARY SEX TRAITS EXAGGERATED WHEN

SYMPATRIC

PREDICTIONS: FEMALES USE DIVERGENT TRAITS TO RECOGNIZE

CONSPECIFICS

PREDICTIONS: COST TO HYBRIDIZATION



Ficedula ssp. Collared Flycatcher by Saetre and colleagues

PREDICTION 1: TRAITS MORE DIVERGENT WHEN SYMPATRIC allopatric

PIED FLYCATCHER COLLARED FLYCATCHER sympatric




PREDICTION 2: PIED FLYCATCHERS SHOULD BE MORE RELATED TO PIED

FLYCATCHERS THAN TO COLLARED FLYCATCHERS REGARDLESS OF

DISTRIBUTION




PREDICTION 3:FEMALES USE DIVERGENT PLUMAGE IN RECOGNIZING

CONSPECIFICS

TESTED SYMPATRIC FEMALES




PREDICTION 3:FEMALES USE DIVERGENT PLUMAGE IN RECOGNIZING

CONSPECIFICS




PREDICTION 4:COST TO HYBRIDIZATION

• Pied Fly Catchers (Ficedula spp.)

-hybrid:75% eggs failed to hatch

-pure pairs: 4.9% failed to hatch

OTHER STUDIES?

North American Drosophila species Trait unknown

Generally Rare

4. RING SPECIATION

POPULATIONS EXPAND RANGE AND BEGIN DIVERGING

-ADJACENT POPULATIONS HAVE GENE FLOW

-END OF “RING” NO GENE FLOW

PREDICTIONS: POPULATIONS EXPAND RANGE IN A RING

PREDICTIONS: GENE FLOW BETWEEN ADJACENT

POPULATIONS EXCEPT AT END OF THE RING


Phylloscopus warblers by Irwin, Bensch and Price

PREDICTIONS: POPULATIONS

EXPAND RANGE IN A RING

PHYLOGENETIC ANALYSES: ORIGIN SOUTHERN TIBET, EXPAND TOWARDS

RUSSIA – MEET IN SIBERIA



PREDICTIONS: GENE FLOW (NO REPRODUCTIVE

ISOLATION) BETWEEN ADJACENT POPULATIONS EXCEPT

AT END OF THE RING

PLAYBACK EXPERIMENTS INDICATE: MALES RECOGNIZE

NEIGHBORING POPULATIONS AS CONSPECIFICS, EXCEPT AT THE END

OF THE RING



PREDICTIONS: GENE FLOW (NO REPRODUCTIVE ISOLATION) BETWEEN

ADJACENT POPULATIONS EXCEPT AT END OF THE RING


OTHER STUDIES?

Ensatina newts of California http://www.pbs.org/wgbh/evolution/library/05/2/image_pop/l_052_05.html

VI. GENETICS OF SPECIATION

A. HALDANE’S RULE: WHEN F

1

OFFSPRING OF TWO

DIFFERENT RACES OR SPECIES ONE SEX IS ABSENT,

RARE OR STERILE IT SHOULD BE THE

HETEROGAMETIC SEX .

-SOME ORGANISMS SEX IS GENETICALLY DETERMINED

VIA SEX CHOMOSOMES


A. HALDANE’S RULE: WHEN F1 OFFSPRING OF TWO


RATE OR STERILE IT SHOULD BE THE

HETEROGAMETIC SEX.

WHY?

1. DOMINANCE THEORY

-dominant alleles “cover” recessive alleles

-some sex chromosomes are degenerate (little fxn)

-thus detrimental sex-linked alleles are no covered in heterogametic sex


A. HALDANE’S RULE: WHEN F1 OFFSPRING OF TWO


RATE OR STERILE IT SHOULD BE THE

HETEROGAMETIC SEX.

WHY?

1. DOMINANCE THEORY

2. FASTER MALE EVOLUTION from Presgraves and Orr 2000


B. POLYPLOIDY: INHERITING

EXTRA COPIES OF

CHROMOSOMES

-COMMON IN PLANTS, LESS

COMMON IN ANIMALS


B. POLYPLOIDY

-IN ANIMALS e.g., salamanders, Ambystoma spp.

Ambystoma jeffersonianum (Southern Range – MD, VA...)

Ambystoma laterale (Northern Range – Canada)

-both species diploid (2n = 28)

28j

14j

14j

28l 14l

14j

14l egg

14j

14l gynogenetic species

A. platineum A. tremblayi

28j

14l or

14j

28l

14l

14l or 14j sperm other polyploid species:

Poecillid fishes, whiptail lizards

SPEC

Is reproductive isolation a direct or by-product of evolution?

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