1. a) What is meant by condition dependent versus genetically determined strategies? b) Use the isopod and a fish example to explain your answer (explain the proximate mechanism in each case).

 

5 Condition dependent the strategies are determined by environmental cues or conditions.

A cue, for example spade-foot toad larvae are converted to carnivores in the presence of fairy shrimp.

A blue-gilled sunfish that grows slowly might adopt one tactic compared to another that grows quickly.

5 Genetically determined strategies arise from a very clear genetic effect without the influence of environment.

 

5 The isopod strategies are determined by two genetic loci, AMS for alternative male strategy and sex-transformer. The AMS locus is the key locus governing development of alpha, beta or gamma males (describe each type).

 

5 Another fish example. Sequential hermaphroditism in reefish are induced to become the aggressive territorial male type, if the current dominant male is removed. The largest female or largest intermediate phase male is changed into the terminal phase male that is territorial under the action of steroid hormones, but the cue is the removal of the dominant (or depredation of a Terminal phase male).

 

 

 

2. a) What is true altruism (what term in HamiltonŐs equation critically distinguishes true altruism from kin altruism)? b) What are the conditions (list the traits) that are necessary for true greenbeard altruism? c) Provide an example of a greenbeard.

 

5 True altruism is a situation in which an individual is willing to bear a cost that benefits an unrelated

3 individual. In kin altruism, the altruist and recipient are related to some degree. Thus, the term in

2 HamiltonŐs equation that distinguishes the two is r, the coefficient of relatedness (r=0 for true altruists, r>0 for kin altruist).

 

5 The traits for true greenbeard:

A signal (in recipient),

Recognition of signal in altruist

Signal recognition elicits social acts on the part of the altruist that benefit the recipient.

 

5 Social act: The lizards in which a blue male is willing to sacrifice all fitness to protect his unrelated blue partner from aggressive orange males. Signal and recognition: The greenbeard in this case consists of the blue allele for sure, a signal, but also other self-recognition genes.

 

If you use the example of greenbeard ants, you must indicate that this is kin nepotism, not strictly altruism as the workers really do not bear a cost. There is a net benefit for the workers and their queen that carries the same allele.


3. a) After an artificial selection experiment for large and smal nest size in mice you reach an upper and a lower plateau (graph the experiment, include controls?). b) What are two reasons why nest size might not be able to continue increasing (or decreasing) under artificial selection (explain both reasons)?

 

a) properly labeled graph (see the one in the lecture notes). 8 points

 

b) Two reasons required:

6pts Pleitropy in which one gene controls the expression of two or more traits. In the case of selection on nest size, reducing nest size makes for females that create an environment that promotes higher mortality in progeny, limiting the effects of selection. (OR in the high lines, perhaps neurotic moms that only spend their time collecting cotton, and ignore other important care-giving behavior to their young).

 

6pts Depletion of additive genetic variation (heritable) under the force of selection. Alleles at loci governing the behavior might fix. Once all the alleles are fixed, there is no genetic variation and selection requires genetic variation (additive in particular) to move traits over evolutionary time.

 

4. a) Explain how one mode of natural selection contributes to speciation. (hint: this mode of selection substitutes for genetic factors promoting speciation that are related to fitness of hybrids). b) What other kind of selection is required to result in sympatric speciation besides natural selection? c) Explain the interplay between the two forces with an example.

 

One mode: disruptive selection generates low fitness for intermediate types.

 

DRAW a picture is useful, or more of an explanation of disruptive to indicate it selects for extremes.

 

(other modes are possible -- directional or stabilizing -- provided the logic is correct).

 

b) Sexual selection and in particular assortative mating is required to generate species.

 

c) The simplest example might be disruptive selection on feeding on two different host plants that have toxins that require special enzymes on the part of insects to detoxify the toxins. The host-plant preference serves as a behavior that generates assortative mating that gets females together with the right males that also share the genes for detoxifying the plant (only they will produce high fitness progeny that can feed on the plant and produce progeny themselves that can find the same plant in the next generation.

5. a) Why might animals appear to be risk aversive? Briefly explain in terms of a bumblebee foraging on flowers and a cognitive model of memory. b) Why do animals gamble (give an example)? What is the adaptive benefit of this behavior? c) How might the mechanism in a) be used to achieve the behavior in b)?

 

8 pts a)

A cognitive model includes:

1) Perception, 2) memory (and data manipulation), 3) forming a representation of the environment, which constitutes a decision rule.

The actual model could be substituted with the description of an experiment showing the phenomena. Howevver, the key issue to point out is memory limits constrain bees: list lengths.

 

6 pts b) Animals gamble because under conditions of food limitation where E return < BMR (sustainance) feeding on the constant or steady reward will certainly lead to death, while gambling allows a lucky few to pass on genes to the next generation. Many examples suffice, but Shrews and Juncoes were population, but bees feeding on sea blush and dwarf huckleberry were also used. You must explain the example.

 

6pts c) by increasing list length when food limited (starving) an animal could readily switch from risk aversive to risk prone foraging decisions.

 

 

6. What hormones are related to aggression? (Describe the action of a reproductive hormone and a neuropeptide). How are these two proximate sources of aggression modulated by other hormones (list a steroid and neurological route by which modulation occurs). YOU MUST DRAW A DIAGRAM for each (e.g., endocrine system and nerve synapse).

 

4pts Most popular answer testosterone. A full diagram of the triangle was not strictly necessary but a diagram with negative feedback loop involving hypothalamus-pituitary-> GnRH -> (LH, FSH) -> T (i.e., HP-gonadal axis) with feedback of T to GnRH was good, as long as there was a cogent description of the action of T.

 

Next popular was the full diagram and the inclusion of the effects of B (adrenal). a diagram like this (but not with the sex chromosomes) [SHOWN below]


4pts The most popular neuropeptide was serotonin, and the description almost invariably included a description of the role of defective MAOA. However, crawfish with the different types of serotonin recepters (1, 2) which either pass on the impulse and the tail flicks or the impulse is blocked, was next popular.

DRAWIN WITH SYNAPSE (minimilastic drawing required).

 

6 pts for each FIGURE for a total of 12pts (with marks taken off if labels were missing or things were incorrect).

Two diagrams were required. These were drawn in lecture (in the case of the endocrine feedback loops, I drew it twice!).