Lecture 22 - Adaptation and its Limits

Question 1

The 3 requirements of natural selection

Answer 1

1. There is variation amongst individuals (almost every single population has infinite variation)
2. Some of the variation is heritable (e.g. height as a trait that shows continuous variation. Distribution of height is almost bell shaped, some height variation gets passed on from parents)
3. Variation effects survival and reproduction (Antler size, mating calls, beak depth, speed)

Any trait that exhibits these features can adapt by natural selection

Question 2

What is an adaptation

Answer 2

a trait currently favoured by natural selection, and previously shaped by natural selection

adaptation is a trait not a process

Question 3

What is the meaning of “adaptive” and “maladaptive”

Answer 3

Adaptive - a trait that enhances fitness

Maladaptive - a trait that reduces fitness

Question 4

What other force other than natural selction can affect evolution of traits?

Can this force lead to adaptation

Answer 4

Genetic drift, allele frequencies change on the basis of chance alone. These changes may have an affect on a trait. The size of changes are likely to be larger in small populations)

genetic drift - random change in allele frequency
natural selection - drives change based on fitness advantages

NO - only natural selection leads to adaptation

Question 5

What does slope of a graph have to be for a trait to be heritable?

Answer 5

Positive slope - heritability
Zero slope - no heritability
Negative slope - ?

Question 6

Is natural selection random?

Answer 6

natural selection is not random (generation of genetic variation may be random, but the election process is not)

Question 7

Define adaptation.

Answer 7

A trait currently favoured by natural selection and previously shaped by natural selection.

Adaptations enhance fitness and allow individuals to leave more offspring than others without the trait.

Question 8

Provide an example of heritable variation from the Galápagos finches.

Answer 8

Variation in beak depth.
Parents with deeper beaks tend to have offspring with deeper beaks.

Question 9

What evidence supports that natural selection acted on Galápagos finch beak depth during a drought?

Answer 9

Birds with deeper beaks survived better because they could crack harder seeds.

Beak depth distribution shifted after the drought, favouring deeper beaks.

Question 10

What is the adaptationist program?

Answer 10

Attempts to understand if a trait is an adaptation by asking:

What is the trait for?
How does the trait enhance fitness?

Question 11

What is adaptive storytelling, and why should it be avoided?

Answer 11

Providing plausible explanations for a trait’s function without evidence.
Misleading because it lacks evidence that the trait affects fitness, is heritable, or varies in a population.

Question 12

Define exaptation and provide an example.

Answer 12

A trait that performs a current function different from the one it originally evolved for.
Example: Feathers evolved for heat regulation but now function in flight.

Question 13

List other explanations for traits that are not adaptations.

Answer 13

Unselected results of physics/chemistry (e.g., blood colour).

Chance (e.g., tongue rolling).

Side-effects of other adaptations (e.g., sneezing).

Historical constraints (e.g., spinal structure in humans).

Question 14

Summarise the key points about adaptation.

Answer 14

Adaptations are favoured traits shaped by natural selection.

Traits vary, are heritable, and affect fitness.

Evolution generates variation randomly, but the selection process is non-random.

Question 15

What is maladaptation?

Answer 15

A trait that reduces fitness or survival in a specific environment.

Example: A trait favoured in one environment may be disadvantageous in another (e.g., lighter skin in high UV areas).

Question 16

What is the difference between adaptation and exaptation?

Answer 16

Adaptation: A trait shaped and maintained by natural selection for a specific function.

Exaptation: A trait that evolved for one function but was later co-opted for another (e.g., feathers).

Question 17

How does genetic drift differ from natural selection?

Answer 17

Genetic drift: Changes in allele frequencies due to chance, often significant in small populations.

Natural selection: Non-random process where traits that improve fitness are favoured.

Question 18

Provide an example of a historical constraint on adaptation.

Answer 18

Example: The human spine.

Evolved for quadrupeds and adapted for bipedalism, leading to issues like back pain due to gravity.

Question 19

Why is natural selection not a random process?

Answer 19

The generation of genetic variation (e.g., mutations) is random, but natural selection favours traits that improve fitness in a specific environment.

Question 20

What are some limitations of the adaptationist program?

Answer 20

Overemphasis on assuming all traits are adaptive.
May overlook:

Traits resulting from genetic drift.

Traits constrained by evolutionary history.

Non-adaptive traits shaped by physics or chemistry.

Question 21

What role does fitness play in adaptation?

Answer 21

Fitness is the ability of an organism to survive and reproduce.

Adaptations enhance fitness by improving survival and/or reproductive success.

Question 22

How do you test if a trait is an adaptation?

Answer 22

Demonstrate variation in the trait.

Show that the variation is heritable.

Prove that the trait impacts survival or reproduction positively.

Question 23

What evidence supports that natural selection acts on a population?

Answer 23

Observed changes in trait frequencies over generations (e.g., Galápagos finch beak depth during droughts).

Differential survival and reproduction linked to specific traits.

Question 24

Why does adaptation require heritable variation?

Answer 24

Heritable traits are passed to offspring, allowing natural selection to act over generations.

Without heritability, advantageous traits cannot accumulate in a population.

Question 25

How does environmental change influence adaptation?

Answer 25

Environmental shifts can change selective pressures, favouring previously neutral or maladaptive traits.

Example: Climate change altering habitats and food sources.

Question 26

What is stabilising selection?

Answer 26

Selection that favours intermediate phenotypes and acts against extreme traits.
Example: Human birth weight (extremely low or high birth weights have higher mortality).

Question 27

What is directional selection?

Answer 27

Selection that favours one extreme phenotype, shifting the population mean.
Example: Increase in Galápagos finch beak depth during droughts.

Question 28

What is disruptive selection?

Answer 28

Selection that favours extreme phenotypes at both ends of the spectrum, reducing intermediate forms.
Example: Beak sizes in certain bird species that feed on large or small seeds, but not medium-sized seeds.

Question 29

What is the difference between adaptive radiation and adaptation?

Answer 29

Adaptation: Traits evolved for specific environments.
Adaptive radiation: Rapid diversification of a single lineage into multiple forms
suited for different ecological niches.

Question 30

What role does phenotype plasticity play in adaptation?

Answer 30

The ability of an organism to change its phenotype in response to environmental changes.

Example: Some plants alter leaf shape based on light availability.

Question 31

How does sexual selection contribute to adaptation?

Answer 31

Traits that improve mating success (e.g., bright feathers in birds) may evolve even if they reduce survival.
Example: Peacock tails, which attract mates but increase predation risk.

Question 32

What is the difference between local and global adaptation?

Answer 32

Local adaptation: Traits that enhance fitness in a specific environment (e.g., polar bear fur in Arctic).
Global adaptation: Traits beneficial across multiple environments (e.g., lungs in terrestrial animals).

Question 33

Summarise the evidence supporting evolution through natural selection.

Answer 33

Fossil record showing transitional forms.

Homologous structures indicating common ancestry.

Observable changes in populations (e.g., antibiotic resistance in bacteria).

Molecular evidence like shared DNA sequences across species.