ecology & evolution - lecture 2

8/24/15'

1'

Awesome'Biology'of'the'Day'

Pouyannian'mimicry'

Sexy'female'wasp?'

He'thinks'so!'Fly'Orchid,'Ophrys'insecHfera'

Argogorytes'wasp'

Announcements'

"Ecology:'EvoluHon,'ApplicaHon,'IntegraHon"'by'Krohne'is'required'AddiHonal'copies'will''arrive'at'bookstore'Wednesday'

The'Molles'textbook'is'op*onal.'

The'Making'of'the'FiTest:'Natural'SelecHon'and'AdaptaHon'

Linking'genotype'and'phenotype'

Genotype:'the'geneHc'makeWup'of'an'individual'

Phenotype:'an'observable'measurable'characterisHc'of'an'organism''

Selec*on:'acts'on'phenotype,'but'there'will'only'be'an'evoluHonary'response'if'there'is'a'geneHc'basis'to'the'variaHon'in'phenotype'

Development'

What'Is'EvoluHon?'

Environment'

Phenotype'

Genotype' +

Ecology:'EvoluHon,'ApplicaHon,'IntegraHon''''''''''''''''''''David'T.'Krohne''''''''''''''''''''Copyright''2015'Oxford'University'Press'

8/24/15'

2'

What'Is'EvoluHon?' Change'in'genotype'frequencies'over'Hme'


SelecHon'Drives'a'Change'in'Allele'Frequencies'


Allele'Frequencies'Change'Over'Time'


HardyWWeinberg'(HWW)'Equilibrium'

!

p2'+'2pq'+'q2'=1''

where'p'and'q''allele'frequencies'

p!+'q'=1'HWW'equilibrium'can'be'extended'to'any'number'of'alleles.''A'populaHon'in'HWW'equilibrium'is'not'evolving.'


The'Mechanisms'of'EvoluHon'

Assump*on'of'H

8/24/15'

3'

Clicker'QuesHon'There'are'two'alleles'(B'&'b)'in'a'popula*on,''

f(B)'='0.3'='p'''

What'is'the'f(b)'or'q'in'this'popula*on?'

A''0.7'B.'0.09'C.'0.49'D.'1''

Clicker'QuesHon'There'are'two'alleles'(D'&'d)'in'a'popula*on,''

f(D)'='0.9'='p,'f(d)'='0.1'='q'''

What'is'the'f(Dd)'or'the'frequency'of'heterozygotes'in'this'popula*on?'

A''0.09'B.'0.18'C.'0.81'D.'0.01'

Clicker'QuesHon'There'are'two'alleles'(A'&'a)'in'a'popula*on.'

''If'f(AA)'is'0.7,'f(Aa)'is'0.2,'f(aa)'is'0.1,'what'is'the'

frequency'of'a?'''

A''0.1'B.'0.3'C.'0.2'D.'1''

8/24/15'

4'

Is'this'populaHon'in'HardyWWeinberg'Equilibrium?'

Genotypes' AA' Aa' aa' total'

counts' 900' 90' 10' 1000'

frequency' 0.9' 0.09' 0.01' 1'

f (A) = 0.9+ (0.09 / 2) = 0.9+ 0.045= 0.945f (a) = 0.01+ (0.09 / 2) = 0.01+ 0.045= 0.055

Alleles' A' a' total'

counts' 1890' 110' 2000'

frequency' 0.945' 0.055' 1'

p' q'

p2 = 0.9452 = 0.893q2 = 0.0552 = 0.003 2pq = 2*0.945*0.055= 0.104

But' populaHon'is'NOT'in'Hardy'Weinberg'Equilibrium'

Clicker'QuesHon'There'are'two'alleles'(A'&'a)'in'a'popula*on.'

''If'f(AA)'is'0.7,'f(Aa)'is'0.2,'f(aa)'is'0.1,'is'this'popula*on'in'Hardy

8/24/15'

5'

Selection can cause allele frequencies to change across generations'

Ecology:'EvoluHon,'ApplicaHon,'IntegraHon''''''''''''''''''''David'T.'Krohne''''''''''''''''''''Copyright''

2015'Oxford'University'Press'

Persistent selection can produce substantial changes in allele frequencies over time

'

Each curve shows the change in allele frequency over time under a particular selection intensity. '

SelecHon:'DeniHons'

SelecHon'occurs'when'a'parHcular'genotype'does'not'survive'or'reproduce'in'the'same'proporHon'as'others.''

QuanHed'the'selecHon'coecient'(s)the'proporHon'of'a'parHcular'genotype'that'is'not'represented'in'the'next'generaHon' 'A'selecHon'coecient'of'1.0'means'that'the'allele'is'lethal''


Types'of'SelecHon''

DirecHonal'selecHon'favors'a'trait'shiked'towards'one'of'the'tails'of'the'normal'distribuHon.''Leads'to'a'shik'in'the'mean'trait'value.'


Types'of'SelecHon''

Stabilizing'selecHonindividuals'in'both'tails'of'the'curve'are'at'a'selecHve'disadvantage.''Maintains'the'mean'trait'value'and'reduces'the'variaHon'in'the'trait.'

8/24/15'

6'

Types'of'SelecHon''

DisrupHve'selecHon'occurs'when'the'tails'of'the'distribuHon'are'favored'over'the'intermediate'phenotypes.'Produces'bimodal'distribuHon'of'the'trait.'


overdominance:'selecHon'against'homozygotes;'heterozygote'advantage'

leads'to'stable'equilibrium' sickle

8/24/15'

7'

EvoluHonary'Change:'DeniHons'

GeneHc'drikrandom'changes'in'allele'frequencies'

Gene'owthe'net'gain'or'loss'of'certain'alleles'by'movement'of'individuals''

MutaHon'pressurethe'evoluHonary'change'resulHng'from'new'mutants'


MutaHon'is'the'ulHmate'source'of'all'new'geneHc'variaHon'

HardyWWeinberg'analysis'shows'that'mutaHon'alone'is'a'weak'mechanism'of'evoluHon'

However,'if'mutaHon'is'combined'with'the'force'of'selecHon'then'evoluHon'can'be'quite'rapid'

mutaHonWselecHon'balance''explains'rare'geneHc'disease'

NonWDarwinian'EvoluHon:'GeneHc'Drik'

stronger'in'small'populaHons'

Alleles'can'become'xed'(p=1)'or'lost'(p=0)'over'Hme'

FixaHon'or'loss'is'inevitable'but'unpredictable'


ecology & evolution - lecture 2

Documents