Lesson 3: Evolution and Behavior

Question 1

adaptation

Answer 1

An evolutionary process that results in a
population of individuals with traits best
suited to the current environment

Question 2

fittness

Answer 2

• Survivorship and reproduction
• Works via Natural Selection and related
  processes

Question 3

Population analyses can reveal selection

Answer 3

• Often, we determine if natural selection is at work on a trait by looking at what’s going on with the trait at a population level
• If selection is occurring on the trait, then we
  should be able to see shifts in a population

Question 4

stabilizing selection

Answer 4

The highest fitness in
a population is
shown by individuals
with an intermediate
trait value in the
middle of the
spectrum

• This leads to a narrowing
  of the variety of the
  distribution of traits within
  the population
• and the trait becomes
  stable in the population
  over generations

Question 5

stabilizing selection in cichlid fish

Answer 5

Compared growth rate of fish in
different-sized patches of food

*Used divided trays to create food
patches: dots represent food
*Put one patch in an aquarium with
one “focal fish” – the individual whose
growth will be measured
*Added 4 competitors to each tank so
the focal fish would have to try to
defend its territory (the food patch)

Question 6

Stabilizing selection in cichlid fish (2)

Answer 6

Measured amount of
defensive behavior with
different-sized food
patches

Result was that defending
larger territories required
more work: more chases
per minute

Question 7

Stabilizing selection in cichlid fish (3)

Answer 7

Measured growth rate of fish
defending different-sized
food patches

Result was that medium-
sized territories had the best
balance of cost and benefit.

SO – stabilizing selective pressure for intermediate territories

Question 8

Directional Selection

Answer 8

The highest fitness in
a population is
shown by individuals
with an extreme trait
value at one end of
the spectrum

• This causes the average
  distribution of the trait
  within the population to
  shift in the direction of
  the highest fitness

Question 9

Directional selection in Hawaiian crickets

Answer 9

Directional selection in Hawaiian crickets
Why? A parasitic fly from North America had invaded. This fly finds victims by listening for the cricket calls (so victims are male) and then lays its eggs on the back of the cricket.
The maggots then attack and eat the cricket

Question 10

Drectional selection in Hawaiian crickets RESULT

Answer 10

Result? A serious downside to
being a calling male cricket
There is now Natural selection
against calling but females still
prefer calling (sexual selection)

But the crickets were not going extinct.
Instead there was rapid evolution -
directional selection – for the crickets
to be very very quiet.

Question 11

what had occurred within the male population

Answer 11

A mutation caused males to lose the
sound-producing parts of their wings.
These males did not get attacked and
so survived better than normal males

Question 12

Phenotypic Plasticity:

Answer 12

generally refers to seeing a change in
phenotype when the environment changes – without a change in genotype. (Plasticity refers to (changeability)

Question 13

sexual selection for the females on Kauai

Answer 13

Females on Kauai have
evolved to be somewhat less
choosy than females from
normal populations - they no
longer require males to chirp.
This is sexual selection on
the females.

Question 14

Convergent Evolution for the crickets

Answer 14

Silent males are also spreading in
the population on Oahu because of
the parasitic fly

This is due to a different mutation in
the wing that produces the same
result.

Question 15

Disruptive Selection

Answer 15

The highest fitness in
a population is shown
by individuals with an
extreme trait value at
both ends of the
spectrum

This leads to a split in
the population – with
some having one
extreme trait and
some having the other

Question 16

Disruptive selection in spadefoot toad
tadpoles

Answer 16

Spadefoot toads come in two
main varieties

DETRITIVORES consume detritus
and small invertebrates

CARNIVORES consume
invertebrates

A third group: INTERMEDIATES
are rarer but are generalists

Question 17

Is this due to disruptive selection
against the intermediates? (spadefoot toad tadpoles)

Answer 17

If so, would predict that
carnivores and detritovores have
higher fitness than intermediates

Might see this in terms of feeding
– perhaps intermediates less fit
because they cannot feed as
efficiently

Question 18

Disruptive selection in spadefoot toad
tadpoles—-Growth of the different
morphs when given
detritus as food source:

Answer 18

Detritovores did better
than intermediates which
did better than carnivores

Question 19

Disruptive selection in spadefoot toad
tadpoles —- Ability to catch shrimp as a
function of morphology:

Answer 19

Carnivores did better than
intermediates which did better
than Detritovores

Question 20

Did a “mark-recapture” study to look at
growth & survivorship

Answer 20

Conclusion:
Individuals with specialized traits on
either end of the spectrum have higher
fitness than individuals with
intermediate traits

Question 21

Evolutionarily Stable Strategies I

Answer 21

–We can think of a ‘strategy’ as a mechanism
that an animal has for achieving some goal –
like finding food, or winning mates

–Some strategies will probably work better
than others, so we expect those to be
favored by natural selection

Question 22

Evolutionarily Stable Strategies II

Answer 22

• Strategies that are selected against should
  disappear from the population
• Strategies that are selected for should remain in the population from generation to generation – thus, in evolutionary terms, they are stable

Question 23

Evolutionarily Stable Strategies III

Answer 23

In the event that one single strategy is favored
above all others (It’s OPTIMAL), then the
population should display just one stable strategy (for a particular task) – this is called a pure ESS

• If multiple strategies are equally favored, then they
  should all be stable – this is called a mixed ESS
  and is a source of variation in the population

Question 24

Digger Wasps - a mixed ESS

Answer 24

Digger wasps use two strategies to
obtain burrows
- “Diggers” dig their own burrows
- “Borrowers” use abandoned burrows
so don’t have to dig their own
- Which strategy a wasp uses is
genetic. Diggers always dig and
borrowers always borrow

Question 25

How can two strategies be maintained in the
population? —- Frequency-dependent selection

Answer 25

• Advantage to being a borrower is zero energy
  spent digging
• But this advantage goes away if diggers are
  rare because then abandoned burrows are
  rare.
• If diggers are rare, they are selected for. If
  borrowers are rare, then they are selected for

-Populations can reach equilibrium

Question 26

why do sexes very? sexual selection

Answer 26

Sexual Selection occurs on traits that exist to enhance
1.) the chance of getting a mate
or
2.) of choosing a good one

Question 27

sexual dimorphism

Answer 27

Morphological and behavioral differences between the sexes that arise because males and females have different selection
pressures when it comes to finding and choosing a mate

Question 28

Sexual selection in house finches: Key info

Answer 28

Males are red,
but females are grayish-
brown – probably so they
can hide more easily from
predators

Key Info: Coloration of male
house finches ranges from red to
orange to yellowish mostly due to
health & diet

Question 29

Sexual selection in house finches: hypothesis

Answer 29

Red is a sexually selected trait in
males because females
prefer red males

Question 30

Testable Prediction

Answer 30

TESTABLE PREDICTION: If
females actually prefer to mate
with red males, then red ones
should get mates more easily
than yellowish ones

Question 31

Experiment 1: House Finches

Answer 31

• Quantified plumage color intensity of
  four males
• Allowed females to choose among
  males (measured how much time out of
  two hours the females spent with each
  of the four males)
• Result: females mostly preferred the
  reddest male (p<.05). No difference
  between the middle males

Question 32

Experiment 2: House Finches

Answer 32

Male feathers were dyed to be redder or
less red (plumage index in parentheses is
the original score)
- Allowed females to choose among males

• Result:
• Females preferred the reddest males

Conclusion:
- Red plumage is a sexually selected trait in
house finches

Question 33

In kin selection, individuals can
increase their fitness by helping kin T/F

Answer 33

True

Question 34

individual selection

Answer 34

Natural selection at the level of individuals

Question 35

group selection

Answer 35

-Selection that favors particular groups of individuals over other such groups of the same species

• Idea that an individual might behave in a way that is good for the species even if the individual suffers
• Behavior of Lemmings often portrayed as example of group
  selection

Question 36

Do lemmings commit suicide?

Answer 36

• Lemmings portrayed as
  “committing suicide” by diving
  off cliffs into water during times
  when food is scarce
• The idea is that they sacrifice
  themselves for the greater
  good of saving everyone else.
  This is “group selection”

Question 37

Do lemmings commit suicide pt.2

Answer 37

• Because natural selection
  works on individual genes,
  group selection can only work if
  the sacrifice increases the level
  of the sacrifice gene in the
  remaining population

Question 38

Difficulties with Group Selection

Answer 38

• The problem is that cheaters would
  win.
• Cheaters would invade and
  because they survived better, the
  ‘suicidal’ genes would be lost from
  the population
• In actuality, when population
  numbers are high, lemmings
  disperse to reduce intraspecific
  competition (natural selection)