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evolution > envs lecture 8 > Flashcards

envs lecture 8 Flashcards

1
Q

what are 4 main topics

A

gene flow, genetic divergence; gene flow, selection, and drift; evolution of dispersal and species ranges

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2
Q

what is one of the most common features of life on earth

A

species vary geographically across space

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3
Q

how do species vary

A

with a climate or host of other factors that shape this spatial variation we see in phenotypes

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4
Q

what does studying these patterns of variation allow for

A

us to understand interplay b/w nat selection, genetic drift, and gene flow

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5
Q

gene flow

A

movement of individuals

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6
Q

cline

A

smooth transition in a trait across geographical space

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7
Q

Bergmann’s rule

A

body sizes of mammals and birds increase w/ distance from the equator (clines across large geographic area)

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8
Q

where esle do we see clines of variation

A

in phenotypic features like body size

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9
Q

why does body size increase w/ distance from equator

A

SA to volume ratios

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10
Q

what ratios do large animals have

A

lower SA to volume ratios (high volume)

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11
Q

what ratios do smaller individuals have

A

high SA to volume ratios

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12
Q

compare large vs small individuals

A

large individuals have lower SA to V ratios, lose less body heat than smaller ppl

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13
Q

who loses more body heat small or large ppl

A

smaller

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14
Q

what is Bergmann’s rule an adaptation to

A

living in cold climates; selection acting on body size

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15
Q

what is selection acting on, and where

A

selection acts on body size, across this ecological gradient

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16
Q

when do clines evolve

A

(1) when selection pressures change across space AND (2) when there is gene flow b/w populations

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17
Q

what is gene flow

A

mixing of alleles b/w diff populations

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18
Q

what is 1st important role of gene flow in evolution

A

equalizes allele frequencies and erodes genetic differences b/w populations

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19
Q

what is 2nd important role of gene flow

A

introduces new alleles into a population from other populations where they already exist

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20
Q

what can natural selection do to 2 populations

A

can make them either more or less similar

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21
Q

what does gene flow do to 2 populations

A

only makes them more similar

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22
Q

what does gene flow introducing new alleles into a population play a similar role as

A

mutation in increasing variation in each population

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23
Q

what causes gene flow

A

dispersal

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24
Q

what is dispersal

A

movement of individuals or gametes

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25
Q

what does variation in environment do

A

affects cline shape and placement

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26
Q

what do rivers to to toucans

A

key barriers; affect ability to disperse

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27
Q

where is gene flow ‘easiest’

A

across river head waters

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28
Q

what is migration rate (m)

A

fraction of individuals arriving from another pop in each generation

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29
Q

what is m basically

A

how quickly gene flow erodes genetic differences b/w populations

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30
Q

what is diff in an allele’s frequency before and after migration

A

delta p = m(pm-p) [change in frequency of p equals migration rate * diff b/w allele p’s frequency in migrants - frequency in population]

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31
Q

how do we measure migration if no distinct populations b/c of spatial continuity

A

measure migration in migration variance

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32
Q

what is sqrt of migration variance equal

A

avg. distance b/w birthplace of parent and offspring

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33
Q

what does variance measure

A

(sigma squared), measures spread of distribution around mean

34
Q

what does variance of zero mean

A

all measurements are identical

35
Q

what does larger variance mean

A

more dispersion around mean

36
Q

can variance be negative

A

nope (sigma squared)

37
Q

what can migration lead to over many generations

A

can cause genes to diffuse across landscape, migration variance measures this spread (or diffusion)

38
Q

what is dispersal

A

force that works against pop differentiation or genetic divergence

39
Q

how do we measure genetic divergence

A

Fst (fixation index statistic)

40
Q

what does Fst measure

A

fraction of total genetic variance across 2+ populations resulting from genetic differences b/w them

41
Q

what does Fst = 0 mean

A

identical

42
Q

what does Fst = 1 mean

A

fixed for diff alleles

43
Q

who came up w/ fixation index

A

R.A. Fisher

44
Q

what does Fst increase with

A

as distance b/w pairs of populations increases

45
Q

what are the most divergent populations

A

those that are farthest apart

46
Q

what is isolation by distanec

A

variance in Fst w/r to distance b/w populations (Fst increasing as distance b/w pairs of populations increases)

47
Q

how do gene flow and selection act

A

in opposition to one another

48
Q

what does local selection do to genetic differences

A

selection enhances differences b/w populations

49
Q

what does gene flow do to genetic differences

A

gene flow erodes/erases genetic differences b/w populations

50
Q

what would happen without selection/genetic drift

A

gene flow would make allele frequencies uniform across space

51
Q

what are compromises b/w these 2 extremes

A

clines, other spatial patterns

52
Q

what happens if selection is much greater than migration

A

A2 will be fixed

53
Q

what happens if migration is stronger than selection

A

A2 will be lost

54
Q

how can we estimate the selection coefficient

A

if you have independent measures of allele frequencies in 2 populations and migration rate b/w them

55
Q

gene swamping

A

when immigration onto an island is stronger than selection, frequency of local alleles evolves to zero

56
Q

basically what is swamping

A

when gene flow overwhelms local adaptation

57
Q

how can we calculate cline width

A

when we have clines of variation b/w phenotypes

58
Q

what can we use cline width to figure out

A

estimate strength of selection

59
Q

what is cline width

A

constant * sqrt of migration variance/selection coefficient

60
Q

what can cline width be used for

A

to estimate strength of selection

61
Q

what does higher migration variance mean

A

less abrupt change in allele frequencies across cline

62
Q

what does lower variance mean

A

more allele frequencies abruptly change across cline

63
Q

when does cline get flatter

A

as strength of gene flow increases relative to selection

64
Q

what happens if selection is relatively stronger

A

steeper cline

65
Q

what are tension zones

A

steep clines

66
Q

when do tension zones form

A

when there is selection against hterozygotes

67
Q

basically what are tension zones

A

situation where selection maintains differences b/w populations that are connected by gene flow, but where fitness & selection varies across space

68
Q

what can be used to estimate Fst

A

neutral loci

69
Q

what are neutral loci

A

those that aren’t undergoing selection

70
Q

what happens if Nm is less than 1

A

Fst is 1

71
Q

what does it mean if Fst is 1

A

populations are differentiated

72
Q

what happens if Nm is greater than 1

A

Fst is 0

73
Q

what does it mean if Fst is 0

A

populations are identical

74
Q

basically what does a single migrant per generation prevent

A

prevents drift from causing too much divergence regardless of pop size

75
Q

what are 6 possibilities for species living along env. gradient responding to climaete change

A

OG population, (2) distribution shifts w/ climate change, (3) declining habitat size, (4) dispersal barriers, (5) limited dispersal abilities, (6) range expansion by adaptation

76
Q

what are dispersal barriers

A

prevent some species from tracking the moving envelop of suitable habitat thus distribution reduces

77
Q

what happens to species w/ limited dispersal abilities

A

may not be able to keep up w/ rapidly changing conditions, thus evolve reduced distributions

78
Q

what is range expansion by adaptation

A

species adapts to new conditions, so range expands

79
Q

of all 6 possibilities, which one includes evolutionary change

A

range expansion via adaptation

80
Q

is adaptation to climate change likely or unlikely

A

unlikely

evolution (15 decks)

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