envs lecture 8

Question 1

what are 4 main topics

Answer 1

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

Question 2

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

Answer 2

species vary geographically across space

Question 3

how do species vary

Answer 3

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

Question 4

what does studying these patterns of variation allow for

Answer 4

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

Question 5

gene flow

Answer 5

movement of individuals

Question 6

cline

Answer 6

smooth transition in a trait across geographical space

Question 7

Bergmann’s rule

Answer 7

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

Question 8

where esle do we see clines of variation

Answer 8

in phenotypic features like body size

Question 9

why does body size increase w/ distance from equator

Answer 9

SA to volume ratios

Question 10

what ratios do large animals have

Answer 10

lower SA to volume ratios (high volume)

Question 11

what ratios do smaller individuals have

Answer 11

high SA to volume ratios

Question 12

compare large vs small individuals

Answer 12

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

Question 13

who loses more body heat small or large ppl

Answer 13

smaller

Question 14

what is Bergmann’s rule an adaptation to

Answer 14

living in cold climates; selection acting on body size

Question 15

what is selection acting on, and where

Answer 15

selection acts on body size, across this ecological gradient

Question 16

when do clines evolve

Answer 16

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

Question 17

what is gene flow

Answer 17

mixing of alleles b/w diff populations

Question 18

what is 1st important role of gene flow in evolution

Answer 18

equalizes allele frequencies and erodes genetic differences b/w populations

Question 19

what is 2nd important role of gene flow

Answer 19

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

Question 20

what can natural selection do to 2 populations

Answer 20

can make them either more or less similar

Question 21

what does gene flow do to 2 populations

Answer 21

only makes them more similar

Question 22

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

Answer 22

mutation in increasing variation in each population

Question 23

what causes gene flow

Answer 23

dispersal

Question 24

what is dispersal

Answer 24

movement of individuals or gametes

Question 25

what does variation in environment do

Answer 25

affects cline shape and placement

Question 26

what do rivers to to toucans

Answer 26

key barriers; affect ability to disperse

Question 27

where is gene flow 'easiest'

Answer 27

across river head waters

Question 28

what is migration rate (m)

Answer 28

fraction of individuals arriving from another pop in each generation

Question 29

what is m basically

Answer 29

how quickly gene flow erodes genetic differences b/w populations

Question 30

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

Answer 30

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]

Question 31

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

Answer 31

measure migration in migration variance

Question 32

what is sqrt of migration variance equal

Answer 32

avg. distance b/w birthplace of parent and offspring

Question 33

what does variance measure

Answer 33

(sigma squared), measures spread of distribution around mean

Question 34

what does variance of zero mean

Answer 34

all measurements are identical

Question 35

what does larger variance mean

Answer 35

more dispersion around mean

Question 36

can variance be negative

Answer 36

nope (sigma squared)

Question 37

what can migration lead to over many generations

Answer 37

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

Question 38

what is dispersal

Answer 38

force that works against pop differentiation or genetic divergence

Question 39

how do we measure genetic divergence

Answer 39

Fst (fixation index statistic)

Question 40

what does Fst measure

Answer 40

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

Question 41

what does Fst = 0 mean

Answer 41

identical

Question 42

what does Fst = 1 mean

Answer 42

fixed for diff alleles

Question 43

who came up w/ fixation index

Answer 43

R.A. Fisher

Question 44

what does Fst increase with

Answer 44

as distance b/w pairs of populations increases

Question 45

what are the most divergent populations

Answer 45

those that are farthest apart

Question 46

what is isolation by distanec

Answer 46

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

Question 47

how do gene flow and selection act

Answer 47

in opposition to one another

Question 48

what does local selection do to genetic differences

Answer 48

selection enhances differences b/w populations

Question 49

what does gene flow do to genetic differences

Answer 49

gene flow erodes/erases genetic differences b/w populations

Question 50

what would happen without selection/genetic drift

Answer 50

gene flow would make allele frequencies uniform across space

Question 51

what are compromises b/w these 2 extremes

Answer 51

clines, other spatial patterns

Question 52

what happens if selection is much greater than migration

Answer 52

A2 will be fixed

Question 53

what happens if migration is stronger than selection

Answer 53

A2 will be lost

Question 54

how can we estimate the selection coefficient

Answer 54

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

Question 55

gene swamping

Answer 55

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

Question 56

basically what is swamping

Answer 56

when gene flow overwhelms local adaptation

Question 57

how can we calculate cline width

Answer 57

when we have clines of variation b/w phenotypes

Question 58

what can we use cline width to figure out

Answer 58

estimate strength of selection

Question 59

what is cline width

Answer 59

constant * sqrt of migration variance/selection coefficient

Question 60

what can cline width be used for

Answer 60

to estimate strength of selection

Question 61

what does higher migration variance mean

Answer 61

less abrupt change in allele frequencies across cline

Question 62

what does lower variance mean

Answer 62

more allele frequencies abruptly change across cline

Question 63

when does cline get flatter

Answer 63

as strength of gene flow increases relative to selection

Question 64

what happens if selection is relatively stronger

Answer 64

steeper cline

Question 65

what are tension zones

Answer 65

steep clines

Question 66

when do tension zones form

Answer 66

when there is selection against hterozygotes

Question 67

basically what are tension zones

Answer 67

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

Question 68

what can be used to estimate Fst

Answer 68

neutral loci

Question 69

what are neutral loci

Answer 69

those that aren't undergoing selection

Question 70

what happens if Nm is less than 1

Answer 70

Fst is 1

Question 71

what does it mean if Fst is 1

Answer 71

populations are differentiated

Question 72

what happens if Nm is greater than 1

Answer 72

Fst is 0

Question 73

what does it mean if Fst is 0

Answer 73

populations are identical

Question 74

basically what does a single migrant per generation prevent

Answer 74

prevents drift from causing too much divergence regardless of pop size

Question 75

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

Answer 75

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

Question 76

what are dispersal barriers

Answer 76

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

Question 77

what happens to species w/ limited dispersal abilities

Answer 77

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

Question 78

what is range expansion by adaptation

Answer 78

species adapts to new conditions, so range expands

Question 79

of all 6 possibilities, which one includes evolutionary change

Answer 79

range expansion via adaptation

Question 80

is adaptation to climate change likely or unlikely

Answer 80

unlikely