Question 1A: What are the three basic alternative male mating strategies? Use an example to illustrate them.

In isopods 1. Large, polygynous territory holder.

or sunfish: 2. Medium-sized female mimic, no territory, polygynous.

3. Very small "sperm bomb" that rushes in unnoticed and releases sperm. No territory, polygynous.

(5 points each)

OR

In lizards: 1. Ultradominant territory holder. Aggressively defends harem. Orange.

2. Mate-guarding territory holder. Less aggressive. Monogamous. Blue.

3. Female mimic. No territory, polygynous, sneaks matings with Orange’s harem by sneaking onto his territory.

(5 points each)

Q 1B: What are the two necessary conditions for sexual selection by the runaway process?

1. Female choice is genetic and variable (heritable).

2. Male elaborate trait is genetic and variable (heritable).

Could get full marks just for this, or give a verbal explanation of the process involved, where traits become linked due to differential mating frequencies.

Note: Non-choosy females have no preference is NOT one of the two conditions, since runaway will work if all females are choosy to some extent.

A genetic correlation between choice and trait is a result of runaway, not a condition for it to occur.

"Good genes" indicated by the male trait is not a necessary part of runaway.

 

 

 

 

Question 2A: How do birds orient/navigate?

First, birds may use many of the same orientation tools as other animals. They may use familiar landmarks, sunlight, wind direction, or even wind speed to orient themselves in their environment. Orientation differs from navigation, however, in that the former refers to knowing where in one’s environment one is, while the latter refers to setting a course to reach a destination. (1 point)

Birds use both the sun and the stars to navigate, as was shown by experiments using the Emlen funnel to record zugenruhe direction. To show that birds use the sun, the direction of sunlight received through an aviary window was alterred by 90 degrees using a mirror. If birds use sunlight, then the direction of zugenruhe should also be rotated by 90 degrees, as turned out to be the result. (4 points)

To show that birds use the stars, birds were placed in a planetarium, in which the placement of the north star and all of the constellations could be manipulated. When the night sky is shifted 180 degrees, so that Polaris is now in the south, the zugenruhe should also shift 180 degrees. Again, this was the result. If the actual star pattern used to navigate is learned, young chicks should learn to navigate using a new constellation pattern. If the rotational pattern of the night sky is changed in a planetarium, so that the constellations revolve around another star, such as Betelgeuse, birds learn to navigate using the false constellation map. (9 points total for planetarium experiments)

 

 

 

 

QUESTION 2B:

Outline the experiments showing bees navigate by using polarized light. How do we know that they communicate?

 

Wehner and Rossel discovered that the bees use polarized light by using a screen to shield the hive from direct sunlight, but allow exposure to polarized light through an opening in the top of the shield. Scout bees were still able to perform the waggle dance, and workers were still able to plot the correct course, in the absence of direct sunlight but in the presence of polarized light. (up to 5 points)

If the hive is completely covered by a clear plexiglass shield, which allows the sun to be visible but blocks polarized light, worker bees do not orient themselves correctly, and fly from the hive in random directions. This shows that it is polarized light that the bees use for navigation. (up to 5 points)

Using a shield that allowed only polarized light in the UV wavelengths to reach the hive, bees were still able to navigate, showing that it is specifically polarized UV light that bees use. (not mandatory, but possible to earn points here)

We know the bees communicate because the angle of the scout bee’s waggle dance in the hive influences the angle at which worker bees plot their course when they depart the hive. Thus, the conditions for communication are satisfied: The behavior of the signaller alters the behavior of the receiver. Must clearly indicate that a behavioral response is elicited in workers, not just "the dance was effective," or words to that effect. (5 points)

3. Explain the conditions required for group selection to overwhelm the force of individual selection and relate your answer to Wynne-Edwards' original proposal for addressing how self-limiting reproductive behaviors may evolve in a population. How might genic or individual selection affect the force of group selection (do these other levels work with or against group selection)?

ANSWER: #3. 20 points possible*****

Wynne Edwards proposed the idea of group selection (non-kin based altruism, which refers to individuals limiting their reproductive success for the benefit of the group). He thought that animals would evolve self-limiting behaviors b/c (1-2 of the following sufficed for 5 pts):

*stripping resources is avoided through self-limiting behaviors

*variation in group W (not individual W) is what is important

*the variation in rate of increase or extinction among groups drives group selection pressure

*those groups with self-limiting behaviors are less probable of going extinct

Group selection is actually favored only under very stringent conditions: very strong group selection pressures, small group, and a rapid generation time (greater than or equal to that of individual) of group (5 pts). These conditions, combined with a scarcity of patchily distributed resources (5 pts.) lead to the evolution of self-limiting behaviors. The survival of the group depends on conserving resources or the group will go extinct. Hence, only the self-limiting groups survive. Genic (Ex: t-allele/selfish gene) or individual selection (Ex: cheater strategy) can easily overwhelm group selection (5 pts). In the case of the cheater strategy, an individual that adopts cheating/selfish behaviors will always maximize its own fitness by not engaging in self-limiting behaviors .

4. In terms of optimal foraging, describe and give examples of how learning as a cognitive process and memory as a cognitive process put constraints on the solutions that animals can use during foraging. Do these processes limit optimal foraging and, if so, why?

ANSWER: #4. 20 points possible*****

One of the key assumptions of optimal foraging theory is that animals are omniscient and, thus, have perfect knowledge of their environment (4 pts). An animal must learn and then retain information about its environment when foraging and therefore, learning and memory as cognitive processes are limiting in terms of optimal foraging. An example of learning as a cognitive process that constrains optimal foraging is when animals create a search image for their designated prey item. One specific example given in lecture was the blue jays that formed a search image of a cryptic moth species and were successful in detecting the prey item when only presented with the single prey. But when shown the original cryptic moth species and an additional, different cryptic species the blue jays were not successful in detecting either prey item. The birds were constrained by having to learn a new search image and if they could only learn one search image, then the blues jays couldn't take advantage of other available prey (8 pts). An example of memory as a cognitive process that limits optimal foraging is the idea of list lengths in animals. Specifically, in the bee example it was found that bees have a list length of one flower. This results in risk aversive foraging behavior b/c if the bee can only remember the last flower it fed on, it can't make a comparitive decision on which flowers would be most optimal to visit next. It will choose to visit flowers that supply, say, a consistent 2m l of nectar vs a flower that supplies 6m l of nectar every third flower (8 pts).

5. What factors influence a males decision to adopt monogamy over polygyny and what factors cause a female to enter a polygynous mating over a monogamous one? (Hint: Use graphs of the marginal value theorm and ideal free distribution to illustrate your answer for males and females respectively!)

Total points posible 20.

10 point for the male view and 10 for the female.

Males benefit from monogamy over polygyny when the marginal gains from added offspring by taking an additional mate are reduced (so benefits are low compared to the cost). This is the marginal value theorm, where the optimal descision is to maximize fitness per unit effort (steepest slope). This will happen when: 1) costs of finding another mate are high 2) the osts of defending a mate are high 3) by searching for another mate you lose paternity with your own mate 4) the cost of aquiring another mate are high (they are all well defended) 5) when parental care is essential and the cost is too high to provide to more than one clutch

For females POLYGYNY: The female must benefit more from sharing a male mate with another female than having a mate to her own. This usually occurs when there is little parental care. Furthermore if resources are patchy some males may have resource rich patches while others have poor patches. Females would then benefit by settling where the most resources are and mating with that male. If a male with a good territory has a mate, but sharing these resources with the primary resources is still more than having all of the resources from a low quality patch then a female should settle polygynously. This is analagous to ideal free settlement on resources, and mating with whatever male gaurds that territory.

6. How can female choice lead to exaggerated male traits? Give three hypotheses and discuss them with reference to direct versus indirect benefits to the female.

Total points: 20

This question asks for 4 things: the process of male trait exaggeration, and three reasons for a female preference. Five points were given for each of these.

A male trait is exaggerated when the most extreme male trait is preferred by ome or all females. Thus the males with that extreme trait leave more offspring than those without. The trait will become more and more exaggerated if there is no or little cost to it, and if females prefer the MOST exaggerated.

There are a number of reasons females might prefer these traits. You needed to give three and say whether they reflect direct or indirect benefit to the female. Direct is when the female directly benefits from some result of the trait, while indirect beefits are those transmitted through the males genes to her offspring.

Possible hypotheses are (not all aceptable ones are presented):

Direct benefits: The trait in some way indicates (exaggerated because of his resources or dominnce) that the male provides one of the following to the female:

More of the female's eggs are fertilized, the male has a resource rich territory, the male can protect the female from harrasmet, or the male will courthip feed the female and increase her cluth size.

Indirect benefits:

1) "sexy sons" this was usually presented in conection with the Fisher Runaway process. The female only benefit because her male sons will be chosen by a larger proportion of the females in the ext generation than non-trait males.

2) The trait is some indicator of fitness in the male: this hypothesis could be presented as more than one reason for female choice if adistinction was made between them. Examples are:

increased growth of offspring, increased parasite resistance, good development (symmetry)

Finally a few of you made a good case for sensory biase, which ends up being a benefit through "sexy sons".

For all examples the lin between the trait and the benefit to the feamle (or why the male has an exaggerated one) is necessary!

Question 7

Bat echolocation is definitely a form of communication. For unintended receivers and intended receivers.

5 pts total for using definition and theory of communication.

Definition required:

Part 1: Total of 10 pts for definition and usage of theory of communication:

Communication results when a signaler sends a signal, a receiver intercepts (intended or unintended contrary to some people's answeres), and **this causes a change in the behavior of the receiver**. Many people missed the last part! (automatic 4 or 5 pt deduction depending on the quality of the following explanation).

Some correct usage of theory and definition -- e.g., signaler benefits (e.g., bat to bat communication) and sends out the signal, or the unintended receiver also benefits (5 pts)

Part II Total 10 pts for argument about why it is and why it is not communication.

Explain how both unintended moths/crickets benefit through a process of communication and how bat autocommunicates (e.g., with itself)

gets you full marks (10 pts).

Question 8

In order to get full marks you had to answer both parts (e.g., sentences).

Part I. Describe what unintended receivers and intended receivers are (10 pts).

Part II. Then describe what evolutionary processes lead to honesty or dishonesty (10 pts).

Part I leads to Part II. For example, honesty is selected between intended receivers (an example most of you used was how female choice selects for females to be discriminating and pick honest *and costly* signals of males) or (prey to predator communication tends to be selected for honesty for obvious reasons).

Dishonesty is selected when unintended receivers exploit the signalling *between* two intended signalers. (an example that most of you chose was how the sneaky male is selected to exploit signalling between honestly signalling male-male combatants). but (others chose the evolution of mimicry which was awesome, because, you correctly put two and two together without my direct lecture material pointing this out to you -- all the pieces were there to put together -- Kudos).

If you went out on proximate tangents without discussing evolutionary processes (e.g., selection, good genes, etc). You grade suffered on this question.