Lecture 8

Question 1

define a population

Answer 1

a group of individuals of a single species occupying a given area at the same time

Question 2

define migration

Answer 2

the movement of individuals from one population to another

Question 3

define gene flow

Answer 3

the movement of alleles from one population to another

Question 4

how can we measure gene flow?

Answer 4

use experimental approaches
use neutral genetic markers:
- polymorphic genetic variants that aren’t direct targets of selection
- rule out selection on particular alleles ‘after the fact’ of migration
- let us infer non-selective processes affecting genetic diversity of populations

Question 5

experiment to answer the question: how much gene flow occurs between geographically separated populations?

Answer 5

• establish two populations, fixed for alternative alleles, separated by a given distance
• score FS heterozygotes in offspring
• frequency of heterozygotes = an estimate of gene flow

Question 6

formally define genetic drift

Answer 6

stochastic changes in allele frequency due to random variation in fecundity and mortality

Question 7

what does random mean in evolution?

Answer 7

stochastic (unpredictable or random) evolutionary forces:
- mutation
- recombination
- genetic drift

deterministic (predictable or non-random) evolutionary forces:
- natural selection

Question 8

define population bottlenecks

Answer 8

• a single sharp reduction in abundance, usually followed by a rebound
• causes a loss of diversity

Question 9

define a founder event

Answer 9

• colonisation by a few individuals that start a new population
• colonising group contains only limited diversity compared to the source population

Question 10

why is genetic drift more pronounced in small populations?

Answer 10

• more drastic fluctuations in each generation
• more rapid loss of genetic diversity (i.e. faster time to allele fixation or loss)
• less consistency across replicate populations

Question 11

as distance increases, gene flow

Answer 11

decreases

Question 12

define isolation by distance

Answer 12

accumulation of local genetic variation due to geographically limited dispersal

Question 13

phenotypic variation may be:

Answer 13

• adaptive (‘local adaptation’
• due to genetic drift
• phenotypic plasticity

Question 14

how do we test for local adaptation and plasticity?

Answer 14

reciprocal transplant studies
Genomic analyses

Question 15

define phenotypic plasticity

Answer 15

the ability of a genotype to modify its phenotype in response to a particular environment

Question 16

draw 3 graphs for no plasticity, plasticity, and highly variable plasticity

Question 17

how does phenotypic plasticity occur?

Answer 17

through modifications to development, growth, and/or behaviours under genetic control

Question 18

in what organisms is phenotypic plasticity common?

Answer 18

in sedentary organisms like plants and corals, but also in animal behaviour

Question 19

phenotypic plasticity often is an adaptation to…

Answer 19

unpredictable environments

Question 20

does all phenotypic plasticity result from adaptation?

Answer 20

no

Question 21

describe reciprocal transplant studies

Answer 21

Growth of equivalent genotypes in contrasting environments and comparisons of their relative
performance

Question 22

why are reciprocal transplant studies useful?

Answer 22

• Can separate phenotypic variation into genetic and environmental components
• Enables measurement of selection against non‐local genotypes
• Can provide evidence for/against local adaptation

Question 23

Clausen‐Keck‐Hiesey Transplant Conclusions

Answer 23

• Differences between populations due to BOTH plasticity and genetics
• Evidence for widespread local adaptation
  – Local populations had highest fitness

Question 24

How do we test for plasticity and adaptation in species that we can’t manipulate experimentally?

Answer 24

genomic studies

Question 25

Tradeoffs Associated With Skin Pigmentation

Answer 25

High UV radiation:
– Degrades folate, critical in highly dividing tissues (e.g. embryos, testes)
– May have selected for increased pigmentation
- Strong purifying selection on MC1R in equatorial
regions

Low UV radiation:
– Reduced vitamin D synthesis
- VitD critical for bone development, immunity, etc.
– May have selected for reduced pigmentation

Question 26

was there a history of local adaptation in skin pigmentation?

Answer 26

Numerous genes known to affect skin pigmentation
* These genes show higher between‐population differentiation than most others
–> Evidence supporting a history of local adaptation
* Pigmentation genes show evidence for positive selection in regions with distinctive skin
colouration