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.