Topic 4 - Natural Selection

Question 1

Daniel Dennet and Natural Selection. What was he implying with this statement?

Answer 1

• Darwin’s dangerous idea

- the idea that complex design might not need a designer, but simply produced by natural selection

Question 2

Define adaptation

Answer 2

• a trait that enhances survival or reproduction (ie. to improve fitness)
• these “adaptations” typically tend to become more common in descendants after the ancestor

Question 3

Define fitness

Answer 3

• the success of a GENOTYPE as measured by its contribution to the next generation
• it is heritable
• reproductive success

Question 4

Natural Selection (genetic definition)

Answer 4

• differential contribution of genotypes to subsequent generations (as measured by their ability to survive and reproduce)

Question 5

What is natural selection NOT synonymous with? how?

Answer 5

• evolution
• Evolution can occur outside of natural selection, ex via genetic drift
• and natural selection can occur without an evolutionary change, ex deviants are eliminated for the optimal phenotype

Question 6

When can a trait be considered an adaptation? and what do adaptation reflect?
- name 4 examples from the lecture

Answer 6

• there may be a cryptic advantage
• adaptations may reflect the environment and life history of a species
• Snake: disarticulating skull bones, to swallow larger organisms
• Cacti: small or absent leaves, due to environment
• Orchid: mimicry for pollination via bees
• Red back Spiders: reproductive success by consuming males

Question 7

What are 4 different explanations of observed traits and how they could have gotten to be the way they are?

Answer 7

• a direct result of natural selection
• correlation with another trait that is under natural selection
• genetic drift (ie. effects of chance - this will determine how much and which variation is passed on)
• historical/phylogenetic factors (ie. natural selection or genetic drift that acted at some point in time in the past)

Question 8

What kinds of evidence indicate natural selection?

Answer 8

• correlation of trait frequency with environment
• variation in fitness with environment
• changes in trait (or allele) frequencies between age classes or life stages
• response to perturbation (stresses) of populations or their habitats

Question 9

How can one get to ensuing genetic change?

Answer 9

By being placed under different selective pressures

Question 10

Explain the case of Industrial Melanism in the peppered moth, and the dominance of certain alleles

Answer 10

It was observed that with pollution and darkening of certain bark, so did the dominant melanic allele increase in frequency relative to the pale grey allele typical before that time

Question 11

How did these changes in allele frequencies in the peppered moth change so quickly and the result from what interaction with predators? and which researcher performed the study?

Answer 11

• in less than a century the melanic allele frequency jumped from 1 percent to nearly 90 percent
• this demonstrated a selective advantage for the darker moth
• this is explained by Kettlewell who observed pale moths were attacked by birds more regularly compared to the melanic moths when tree trunks were DARKER

Question 12

What were the two field studies carried out by Kettlewell?

Answer 12

• mark-recapture experiments (release and re-capture of melanic and light coloured moths in polluted/non-polluted environments)
• observe predator behavior (birds foraging on these different tree trunks based on pollution) from bird blinds

Question 13

What was the underlining discovery from Kettlewells first experiment?

Answer 13

• peppered moths that contrasted with their backgrounds (pollution vs non-pollution) were recaptured in smaller numbers

Question 14

What does recent data of the peppered moth show?

Answer 14

• with improved air regulations there has been a steady decline in the melanic form of the moth as the environment is cleared up

Question 15

Explain how Natural Selection has affected the European land snail.

Answer 15

• there is an association between the shell colour of the snail and the banding pattern with the habitat
• birds tend to prey on the LEAST common shell banding pattern in the habitat (targeted for bird predation)

Question 16

How does natural selection act on Guppies and two of its predatory fishes? and what is this an example of

Answer 16

• There is a tradeoff between having more conspicuous spots on the guppy itself
• the more conspicuous the spots on the fish, the more attractive it is for mating
• however the outcome from this is that the additional spots make it more attractive from predation
• this is an example of Male Reproductive Success
• conflicting selection pressures

Question 17

Explain the two cases of RAPID ADAPTIVE evolution in soapberry bugs. Comparing Florida and Texas.

Answer 17

1. In Florida, the soapberry bugs native host is a large ballon vine, which require a long beak to reach the seeds on the inside - over 50 years with an introduced host has a shorter distance to its seed, so the beak length decreased
2. Compared to Texas, the opposite occured

Question 18

Explain how the length of Atlantic Cod changed as a result of what factor? and what two effects where felt by the species

Answer 18

• rapid adaptive evolution
• fisheries for year targeted to larger and fish reaching maturity
• thus younger fish began reaching sexual maturity much earlier in their lives and subsequently when smaller fish were favoured
• thus there selection favouring early reproduction at smaller sized fish which INCREASED its effect on adding to the gene pool
• thus there were both ecological and genetic effects on the species

Question 19

Explain how Bighorn sheep were succumb to rapid adaptive evolution.

Answer 19

• the mean horn length of 4 year old bighorn sheep rams DECLINED because of selection imposed by hunting the larger horned sheep

Question 20

What are two essential criteria for natural selection?

Answer 20

• fitness-related variation

- heritability of this variation

Question 21

What else can Natural Selection act on besides individuals?

Answer 21

• it can act at other levels of organization as well, such as
• genes
• kin groups and populations
• species

Question 22

What is heritability restricted to?

Answer 22

• to living beings, non-living beings lack the ability

Question 23

In what way can genes be selected on to the detriment of the individual?

Answer 23

• selfish genetic elements can proliferate in a genome (even if it is detrimental to the individual)

Question 24

What can distort Mendelian inheritance and what will this look like?

Answer 24

• selfish alleles of a gene, where they are passed on at a higher rate than other alleles at that locus

Question 25

Give an example of selfish alleles and explain the importance of the heterozygous mouse.

Answer 25

• the T/t locus in mice
• where TT mice, homozygous have the normal allele
• where Tt mice, heterozygous will pass on both alleles equally but most of the sperm carry the t allele
• where the tt mice, homozygous will die early or be sterile

Question 26

What has natural selection in groups been used to explain?

Answer 26

• these groups are kin groups, populations
• and this has been used to explain ALTRUISTIC TRAITS (traits with a cost to the individual exhibiting them - but a benefit to one or more other individuals)

Question 27

Define altruistic traits and what it cannot evolve by?

Answer 27

• a feature that reduces the fitness of an individual that bears it for the benefit of the population or species
• it CANNOT be evolved by individual selection

Question 28

What is the difference between a selfish allele and an altruistic trait?

Answer 28

Are they the same thing?

Question 29

How do altruistic traits exist?

Answer 29

• through group selection where certain individuals suffer from having this trait - and UNFORTURNATE DISADVANTAGE

Question 30

What did the result of conflict between individual and group selection lead to?

Answer 30

• the evolution of altruistic traits

Question 31

What two individuals examined the conflict between individual and group selection?

Answer 31

• Wynne-Edward

- Williams

Question 32

Natural Selection on individuals counteracts natural selection on groups

Answer 32

Natural Selection on individuals counteracts natural selection on groups

Question 33

What did Wynne-Edwards refer to in his idea between the conflict of individual and group selection?

Answer 33

• he stated altruistic behavior will evolve because group selection favours it

Question 34

What did Williams refer to in his idea of the conflict between individual and group selection?

Answer 34

• within-population selection favours the SELFISH allele and increases it more rapidly than the whole-population events, so the SELFISH allele will become fixed

Question 35

Define Species selection

Answer 35

• selection among groups of organisms
• when the groups involved are species and there is correlation between some characteristics and the rate of speciation or extinction

Question 36

Species selection will occur when there is a correlation between what?

Answer 36

• the proportion of species that have one character state rather than another character state changes over time
• ex. speciation rate and morphological character

Question 37

Where are the consequences of natural selection when it acts on individual units?

Answer 37

• the consequences are in the population

Question 38

If Natural Selection acts on phenotypes, what else changes?

Answer 38

• there are changes in allele frequencies

Question 39

Natural selection cannot see into the future?

Answer 39

• it can only act on the present conditions

Question 40

Why can’t natural selection lead to perfect adaptations?

Answer 40

• it can only favour the fittest available phenotype, and is always compromise among opposing pressures
• natural selection does not OPTOMIZE