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Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages in tissue formation. Individual Selection: Darwinian selection. *Group Selection*:Selection among groups. Kin Selection Interdemic or Inter-population Selection Species Selection: selection among taxonomic lineages.

Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

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Page 1: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Levels of Selection

• Gametic Selection: meiotic drive or segregation distortion is selection among gametes.

• Cell Selection: selection among cell lineages in tissue formation.

• Individual Selection: Darwinian selection.• *Group Selection*:Selection among groups.

– Kin Selection– Interdemic or Inter-population Selection

• Species Selection: selection among taxonomic lineages.

Page 2: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Necessary Properties for Evolution by Natural Selection

• Phenotypic Variation: There must be differences among the units in phenotype.

• Fitness Variation: The phenotypic differences must result in differences among the units in birth and death rates.

• Genetic Variation: The differences in phenotype that cause the differences in fitness must be heritable:

Page 3: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Levels of Selection

• Selection Among Individuals within Groups is Standard Darwinian Selection

• Selection Among Groups of Individuals is Controversial.

Page 4: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

“I confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory. I allude to the neuters or sterile

females in insect-communities: for these neuters often differ widely in instinct and in structure from

both the males and fertile females, and yet, from being sterile, they cannot propagate their kind.”

Darwin 1859

Problem: Sterile female workers have a fitness = 0 and cannot propagate their own kind.

Page 5: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

“This difficulty, … as I believe, disappears, when it is remembered that selection may be applied to the

family, as well as to the individual, and may thus gain the desired end.”

Darwin 1859

Solution to Problem: Selection applied at a higher level of biological organization: Selection among

families or among colonies.

Page 6: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

“ (Problem=) Breeders of cattle wish the flesh and fat to be well marbled together: an animal thus

characterised has been slaughtered, but (Solution=) the breeder has gone with confidence to the same

stock and has succeeded. .”Darwin 1859

Typical Darwinian style of argument: Uses example from artificial selection of domesticated

plants and animals.

Page 7: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

“Here is a better and real illustration: according to

M. Verlot, some varieties of the double annual Stock from having been long and carefully selected to the right degree, always produce a large proportion of

(Sterile Offspring = ) seedlings bearing double and quite sterile flowers; but they likewise yield some single [flowers] and fertile plants (= Reproductive

Offspring). These latter, by which alone the variety can be propagated.”

Darwin 1859

Page 8: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

These latter, by which alone the variety can be propagated, may be compared with the fertile male and female ants, and the double sterile plants with the neuters of the same community. As with the

varieties of the stock, so with social insects, selection has been applied to the family, and not to the individual, for the sake of gaining a serviceable

end.

Darwin 1859

Page 9: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Benefactors Recipients

Bear fitness cost of altruismand bestow fitness benefit

on group members

No fitness cost because they are not altruistic, but a fitness benefit,

reap fruits of theBenefactors in the group

Wbenefactor < Wrecipient

Page 10: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Group 1: Pbenefactors = 0.80 Group 2: Pbenefactors = 0.20

Two kinds of Phenotypic Variation: (1) individuals differ from one another; (2) groups differ from one another

in frequency of benefactors and recipients .

Page 11: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Individual Selection Within Groups Opposes Benefactors

Before:

After:

Individual Selection Within Group 1:

pbenefactors = 0.78 – 0.80 = - 0.02 Individual Selection Within Group 2

pbenefactors = 0.17 – 0.20 = - 0.03

Average pindividual = (- 0.02)(0.6) + (- 0.03)(0.4) = - 0.027 < 0

Page 12: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Benefactors0

1

Directional Individual Selection within groups: Benefactors reduce their own relative fitness and increase fitness of others.

Low Fitness

High Fitness

Fit

nes

s of

In

divi

dual

Recipients

Behavior Phenotype

Page 13: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Group 1: Many Benefactors Group 2: Few Benefactors

Group Fitness Variation: group growth rate increases with the frequency of benefactors.

Before:

After:

Page 14: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

AfterReplication:

pgroup = {(0.8)*(1.2) + (0.2)*(0.8)}/2 – 0.5 = +0.06 > 0

Group Selection Favors Benefactors:Groups with more benefactors grow faster thanGroups with few benefactors.

Page 15: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

More Benefactors0

1

Directional Group Selection among groups: Groups with a high frequency of benefactors Grow faster and to larger size.

Low Fitness

High FitnessF

itn

ess

of G

rou

p

Few Benefactors

Group Behavior Phenotype

Page 16: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Directional Group Selection F

itn

ess

of G

rou

p

Group Behavior Phenotype

0

1

Directional Individual Selection

Fit

nes

s of

In

divi

dual

0

1

Individual Behavior Phenotype

TWO Opposing Levels of Selection

Page 17: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Selection Among Groups: pgroup = {[(0.8)*(1.2) + (0.2)*(0.8)]/2} – 0.5 = +0.060 > 0

Selection Within Groups: pindividual = (- 0.02)(0.6) + (- 0.03)(0.4) = - 0.027 < 0

ptotal = pindividual + pgroup = - 0.027 + 0.060 = +0.033When Group Selection is stronger than Individual

Selectionthe Benefactor Type INCREASES.

ptotal = /Total}{

After

/Total}{

Before

-

Total Selection: Sum of Within and Among Group Selection

Page 18: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Opposing Evolutionary Forces• Natural Selection versus Deleterious Mutation

Reach a balance where every copy of a deleterious allele removed from a population by selection is replaced by mutation.

• Natural Selection versus Sexual SelectionTraits that increase male mate numbers at the expense of

male viability spread through a population.• Group Selection versus Individual Selection

Traits that increase the fitness of the group can spread at the expense of the individual when group selection > individual selection.

Traits that increase the fitness of the individual can spread at the expense of the group when individual selection > group selection = Tragedy of the Commons

Page 19: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Selection at any higher level than that of an individual is essentially "impotent“ and is "not an appreciable factor in

evolution" (1966:8; cf., Williams 1992).

“Many, perhaps most, evolutionary biologists believe that it [group selection] is only rarely an important force of evolution.”

(Futuyma 1998, p. 352)

Group vs. Individual Selection Controversy

Page 20: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

It is sometimes said, “Group selection was vanquished in the 1960s by William Hamilton and

his ‘gene’s eye view’ of selection, which is the basis of Richard Dawkins’ notion of the selfish gene.”

“The fundamental unit of selection, and therefore of self-interest, is not the species,

nor the group, nor even, strictly, the individual. It is the gene, the unit of heredity.”

(Dawkins, 1976)

Page 21: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Group vs. Individual Selection

Property Individual GroupPhenotypic Variation Large Small

FitnessVariation Large Small

Association between

phenotype and fitness

Common Rare

Page 22: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

The Biology of Group Phenotypes

• Artificial Individual and Group Selection on Migration in the flour beetle,

Tribolium confusum (Craig 1982)

Page 23: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Individuals differ in tendency to emigrate and the differences are genetic

Phenotypic variation

Vmigration > 0

And it is heritable

VGenetic > 0

“Stay at home” beetle

“Traveling” beetle

Page 24: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Variation in Group Density leads to Variation in Group Migration

Low density = every beetle is morelikely to “stay home”

High density = every beetle is morelikely to be “traveling”

Page 25: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Variation in Group Density leads to Variation in Group Migration

Low density = every beetle is morelikely to “stay home”

High density = every beetle is morelikely to be “traveling”

Group Density Variation

VDensity > 0

And Density is heritable

VGenetic > 0

Page 26: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

High Density

Low

High

High Density Causes Increased Migration

Low Migration

High Migration

Mig

rati

on P

hen

otyp

e of

Gro

up

Low Density

“Social” Environment

Page 27: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

0

1

Directional Individual Selection imposed by Dr. Craig: Experimentor creates variation in fitness: VW > 0 and the association between migration and fitness

Low Fitness

High Fitness

Fit

nes

s of

In

divi

dual

“Stay at home” beetle“Traveling” beetle

Page 28: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

High Migration = High Density

0

1

Directional Group Selection imposed by Dr. Craig: Group (High)Experimentor creates variation in group fitness: VGroup W > 0

and association between Migration and Group Fitness

Low Fitness

High Fitness

Fit

nes

s of

Gro

up

Low Migration =Low Density

Page 29: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

0

1

Low Fitness

High Fitness

Fit

nes

s of

Gro

up

High Migration = High Density

Low Migration =Low Density

Directional Group Selection imposed by Dr. Craig: Group (Low)Experimentor creates variation in group fitness: VGroup W > 0

and association between Migration and Group Fitness

Page 30: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

“Stay at home” beetle High Fitness

Individual Selection Group SelectionNone NoneControl

NoneInd Low

Group Low Low MigrationHigh FitnessNone

Ind & Group Low“Stay at home” beetle

High Fitness

Low MigrationHigh Fitness

Ind Low Vs Group High “Stay at home” beetle

High Fitness

High MigrationHigh Fitness

High MigrationHigh Fitness

Group High None

Page 31: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Experimental Test for measuring Migration

160 beetles Empty

Page 32: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Experimental Test for measuring Migration

160 beetles Empty

Pipe Cleaner and string

Page 33: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Experimental Test for measuring Migration

Less than 160 beetles Migrators

Pipe Cleaner and string

Page 34: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Results of 14 Generations of Artificial Selection

Treatment

Migrators

Out of 160

% of

Control

Only Individual Selection (Low)

91.95 - 4.9

Only Group

Selection (Low)

67.85 -29.9

Only Group

Selection (High)

118.2 +22.2

Ind versus Group

(Low vs High)

112.4 +16.2

Ind & Group (Low)

80.79 -16.5

No Selection

Fewer thanControl

Much Fewer Than Control

Much More Than Control

Much More Than Control

Surprizing!

Page 35: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Experimental Test for measuring Offspring Density

30 Adult beetles

Wait 40 Days

Page 36: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Experimental Test for measuring Offspring Density

30 Adult beetles

40 Days

Hundreds of Offspring

Page 37: Levels of Selection Gametic Selection: meiotic drive or segregation distortion is selection among gametes. Cell Selection: selection among cell lineages

Results of 14 Generations of Artificial Selection

Treatment

Offspring

Density

% of

Control

Only Individual Selection (Low)

846 +1.6

Only Group

Selection (Low)643 -22.8

Only Group

Selection (High)886 +6.4

I vs G

(Low vs High)891 +7.0

I and G (Low) 710 -14.8

No Selection

Equal toControl

Much Fewer Than Control

More Than Control

More Than Control

Surprizing!

1% ~10 offspring