1 a) What are the two conditions
for an ESS (4 points)?
1) The strategy, when rare, can invade all other strategies
2) Once common, the strategy can limit the invasion of other strategies
(or, other strategies cannot invade the strategy when common)
b) When is hawk an ESS (2
pts)? When can dove invade (2 pts)? Use words or a payoff matrix.
This question required some statement about lethal fighting. For Hawk to
be an ESS lethal fighting must be rare/absent (stated mathematically with a
payoff matrix drawn, V>C).
For Dove to be an ESS, fighting must be lethal in Hawk (stated mathematically with payoff
matrix, C>V).
c) What is an
Evolutionarily Stable State (ESState) (4 pts)?
Contrast an ESState with an ESS (2 pts).
An ESState is a situation where no one
strategy exists as an ESS (e.g., both conditions satisfied) and the population
exists as a polymorphism of strategies. In short an ESState
violates the second criterion listed in 1a. In contrast an ESS satisfies both
conditions and the population exists as a monomorphism.
d) Is the RPS and ESState (3 pts)? Explain with an example (3 pts).
Yes the RPS exists with 3 strategies that are unable to outcompete the
other two and win. The simplest example is the lizards, or isopods, or fish, or
dragonflies (and a short biological description was required).
2 a) What
are the two critical conditions for sympatric speciation?
Assortative mating (variations on this were allowed, non-random mating
when it was clear for species type)
Hybrid unfitness (variations on this were allowed)
b) Why do behavioral
isolation mechanisms between species evolve? Isn't sterility enough to keep
species from mixing?
A simple way to answer this is in terms of a female that is choosy for
her own type (species) that picks males with clear signals of species type. She
(and he) will have higher fitness than females (and males) engaged in hybrid
mating. Variations on this concept were allowed.
c) How
does the evolution of host-plant choice satisfy the conditions required for
sympatric speciation? A drawing might help you explain your answer.
Full marks required a statement of how assortative mating requirement is
satisfied: This is via preference for plant species (shared in both males and
females) AND a statement of how hybrid unfitness requirement is satistifed: This is via local adaptation of insect (that
survives) to the plantÕs toxin; the insect carries detoxification ability to
the plant toxin.
Then there are different species
of plants with different toxins that generate hybrid unfitness (e.g., when the
preference genes and toxin genes become scrambled), relative to the types that
specialize on plant via preferences and detoxification ability (and breed true
to the species type).
3)
a. What is the central assumption of optimal foraging
theory? (4 pts)
Maximize energy intake per
unit time. The value of an item is made up of the cost of acquiring the item
and time taken to find the item. Animals make decisions based on temporal constraints (time
taken to find/process food), energetic constraints (metabolic costs of
foraging, processes per unit time), cognitive constraints,
processing contraints (handling time, minimum
and maximum size of prey).
b.
Draw a graph explaining the marginal value theorem, showing the point at
maximum net gain for the animal in a patch, travel time and time in patch.
Label the axes. (5 pts)
Please
refer to Chapter 6, pg. 115 for the graph.
MVT specifies when an
organism should leave a patch it is exploiting. As an animal begins to feed, energy gain slows down when
food is scarcer. The marginal
value or the amount of energy in the patch declines as the patch is
exploited. MVT takes into account
the amount of time in a patch and travel time between patches. A steep slope that still touches the
curve will maximize teh rate of energy gain. With a short travel time, an organism
leaves the patch sooner than if the travel time between patches is long. This
question was strictly speaking about foraging for food (not for mates or
copulations).
c.
When might an animal appear to be risk aversive? (2 pts)
Animals like juncos opt to
feed at stations that supply a constant rate of food, avoiding feeding stations
with variable amounts of food during food plenty conditions because risk is not
rewarded. It takes twice as much
food at risky stations for birds to forage in them equally as constant-reward
stations. An animalÕs memory
window is also important in their decisions to be risk averse.
d.
When might an animal appear to be a gambler? (2 pts)
When shrews are starving,
they are willing to gamble on risk-prone foraging because if they stay at
constant reward rations, they face certain starvation and canÕt feed fast enough
to survive. At risky reward
stations, most animals face death but some will have good luck and survive.
e.
Explain the scenarios when a bumblebee foraging on flowers can be risk aversive
and a gambler. (1 pts)
When honey was removed from
bumblebee colonies, bumblebees from that colony switched foraging preferences
from constant reward to variable reward flowers. When honey was added to colonies, bumblebees switched back
to constant reward flowers. Bees are sensitive to reward risk; the colony reserves
caused a switch in individual bee behavior.
Total
14 pts
(Taken from
Chapter 6, Study Questions #1, #4)
4. a. Describe a mutation experiment that was used to isolate a gene for nurturing in mice. What behaviors did the altered mice not perfom? (8 pts.)
Through a mutagenesis
experiment, researchers deactivated the gene fosB in
mice. Mice lacking this gene did
not exhibit nurturing behavior.
They neither retrieved their young nor nursed them. However, the mice were able to perform
other tasks, such as maze-running and olfaction tests. Also, their mammary glands were normal.
Description of
experiment: 2 pts. Students basically just had to state that researchers
deleted the gene fosB from mice. If they forgot or misstated the name of
the gene, I took off ½ pt.
Description of
behaviors not performed: 6 pts. (3 pts. per behavior) If the students just said
that the mice did not nurture, I gave 2/6 pts., since
that was fairly obvious from the way the question was phrased. If students listed one behavior and
also said that the mice did not nurture, I gave 4/6 pts.
While IÕve included
it in my answer, I didnÕt give any extra points for the description of the
behaviors the mice could perform, since those were stated in part c of the
question.
b. Which of Niko TinbergenÕs four questions about behaviors was this experiment trying to answer? (2 pts.) Was this a proximate or ultimate question? (2 pts.)
This experiment was
trying to answer TinbergenÕs question of causation, since it concerned itself
with which genes were directly responsible for the behavior of nurturing in
mice.
Causation is a
proximate, or ÒhowÓ question, since it does not ask why the behavior evolved,
only how it arises mechanistically.
On this question, I
gave two points for saying that it was a causation question, and two points for
stating that it was a proximate question.
A lot of people said that the question was causation and something else,
or both proximate and ultimate. I
took off one point for each of those errors.
c. Why was it important to show that the non-nurturing mice could perform other tasks, such as maze-running or olfaction tests, and that they were physiologically normal? Hint: If the mice had failed in these other tests, that would have meant a certain genetic effect was confounding the results of the experiment. What effect is it?
If the mice had
failed the maze-running or olfaction tests, or if they had not had normal
mammary glands, that could have meant that the lack of nurturing behavior was a
pleiotropic consequence of fosBÕs
effect on sense of direction, sense of smell, or mammary gland formation. This would confound the results of the
experiment because it would mean that fosB was not a
gene specifically for nurturuing, but rather had pleiotropic effects on nurturing through its effects on
other aspects of mouse physiology or behavior.
Here, I gave 4 points
for the correct answer to the Ògenetic effectÓ question (pleiotropy). I gave 4 points for the explanation of
how pleiotropy could have confounded the results of the experiment.