Name: KEY

 

QUESTION A.  What does it mean for an animal to behave optimally? What are the steps involved in constructing a model of optimal behavior? What must be measured in order to construct any such model? Illustrate your answer with an example of such a model and how it can be used to make testable predictions.

 

Answer A.

1)    Body of theory at heart of modern behavioral ecology. Behavior is assumed to be shaped by natural selection for behaviors that maximize fitness.

 

2)    Explains behavior in terms of a benefit/cost approach.

 

3)    There are four steps to building an optimality model. First, you must specify the kinds of behaviors possible in a given situation. Only look at possible, or plausible, behaviors.

 

4)    Second, choose the "currency" that is being maximized. This currency should be related to fitness, either directly (as in number of offspring produced), or indirectly (as with foraging models that assume maximizing some aspect of energy acquisition results in greater fitness for the organism).

 

5)    Third, determine the costs and benefits of each possible behavior in terms of the currency identified.

 

6)    Last, compare the possible behaviors in terms of their benefit/cost ratios and identify the behavior will maximize fitness relative to the other possible behaviors.

 

7)    This allows us to make testable predictions about behavior. Examples of particular models help explain these ideas, particularly with respect to what you can measure in terms of currencies, etc.

 

8)    Writing and organization

 

 

QUESTION B. The Tasmanian native hen is a flightless bird in which males often outnumber females.  In this system, either a pair (male and female) raise offspring by themselves, or a pair is helped by a subordinate male. The subordinate male is either unrelated to the male and female, or a brother of the male of the pair. Given the following data:

 

a. First year breeding pairs (no helpers) average 1.1 offspring produced during that year. 

b. First year breeding trios (Male and Female + subordinate male) produce 4.1 offspring on average.

c. Experienced pairs (not first year breeding) produce about 5.5 offspring per year without helpers.

d. Experienced pairs (not first year breeding) with helpers (i.e. a trio) produce about 6.5 offspring per year.

 

If a male is faced with three choices -- breed on its own, help a brother in his first year, or help an older, experienced brother -- which should it choose and why.  In answering the question, explain HamiltonÕs rule in detail, as well as kin selection, show your work and calculations, and state which of the three options is best, second best, and worst. (Remember, helpers are helping raise nephews/nieces, not siblings).

 

Answer B.

 

1)    Apparently altruistic acts can sometimes be explained by kin selection, in which an individual (the donor) sacrifices its own survival or reproduction in favor of another individual (the recipient) to which it is related by common descent.

 

2)    Fitness can be either direct (producing one's own offspring) or indirect (helping produce relatives' offspring).

 

3)    The indirect fitness component is calculated based on the increase in reproductive success resulting from the help provided by the donor weighted by the relatedness of the donor to those offspring.

 

4)    Hamilton's rule provides the basis for calculating the costs and benefits of helping. In its simplest form, Hamilton's rule is: r*B>C, where r is the coefficient of relatedness, B is the benefit of help to the recipient, and C is the cost to the donor.

 

5)    When calculating whether "altruism" will be selected for through kin selection, it is useful to define B and C in term of offspring and weight each by the coefficient of relatedness to the donor. This changes the equation to be:

 

a.     rB * B > rC * C  or, written another way  B/C > rC / rB

 

6)    We can use this form of the equation to solve the Tasmanian Hen problem.

 

a.     Relatedness of donor to own offspring (rC) = 0.5

b.     Relatedness of donor to brother's offspring (rB) = 0.25

c.     C = cost in terms of own direct fitness = 1.1 offspring on average

d.     Bhelping first year brother = 4.1 – 1.1 = 3.0 offspring (extra offspring produced via help)

e.     Bhelping experienced brother = 6.5 – 5.5 = 1.0 offspring (extra offspring produced via help)

 

7)    At this point, you can either compare ratios from the above equation, or you can just figure out proportion of genes transferred to the next generation by a first year male in all three of these choices. These are:

a.     1.1  * 0.5 = 0.55 (cost – also benefit of breeding along – direct fitness)

b.     3.0 * 0.25 = 0.75 (benefit of helping first year brother – indirect fitness)

c.     1.0  * 0.25 = 0.25 (benefit of helping experienced brother – indirect fitness)

d.     Either method has the same result,

1.     helping a first year brother gives the greatest benefit,

2.     breeding alone,

3.     helping an experienced brother.

 

8)    Writing and organization

 

 

QUESTION C. Explain the concept of Inclusive Fitness. Use an example of your choice to illustrate the concept. Be sure to include explanations of Direct and Indirect Fitness. Finally, should extra-pair fertilizations (EPFs) be counted as Direct of Indirect fitness? Explain.

 

ANSWER C

 

1.       WD. HamiltonÕs Logic:

a.       Relative fitness, ultimately, measured as number of genes transmitted to next generation - obviously own offspring do this

b.       Animal has genes in common not just with offspring, but with  other relatives (cousins, siblings, nephews, etc)

c.       Thus, behavior promoting reproduction of relatives can also enhance fitness and in some circumstances be selected for even if that behavior reduces production of an animalÕs own offspring

 

2.       WD Hamiltons Inclusive Fitness Definition: def: overall genetic contribution to subsequent generations of an animalÕs own breeding success PLUS the effect of its behavior on breeding success of animalÕs sharing its genes by common descent

 

3.       Consists of 2 components

a.     Direct Fitness – your own offspring – you are related to your offspring by r=0.5

b.     Indirect fitness – offspring of your relatives that were produced DUE TO YOUR BEVAVIOR

 

4.       Leads to Kin Selection  - def: selection for behavior that lowers an individualÕs own chance of survival and reproduction but raises the chances of survival and reproduction of a relative

 

5.       Example – effectively used

 

 

6.       How do EPFÕs count? Direct or Indirect Fitness?

a.     Direct – the EPF father/mother gets direct fitness

b.     Indirect – if your mate has offspring with your relative, then you raise them, it is Indirect, so you donÕt care about the EPF

c.     NONE – if your mate has offspring with non-relative of yours, you are out of luck altogether

 

7.            Writing and organization

 

 

QUESTION D.   Explain Figures 2 and 3a from Cratsley and Lewis (2003) and use these figures to explain sexual selection in terms of ZahaviÕs Handicap principle.

 

  1. Cratsley and Lewis (2003) investigated sexual selection and female choice in fireflies. Specifically, they looked at the value of male flashes as an honest signal females use in mate choice.

 

  1. Fig A relates spermataphore mass to flash duration. A spermataphores are protein masses males provide the female as a Ōnuptual giftĶ. Although in many systems females choose males based on Ōgood genesĶ or other indirect benefits. The spermataphore is a direct benefit to females, since it is the primary source of nutrients available to females during reproduction. Thus, there should be selective pressure on females to accurately assess males that can provide large spermataphores.

 

 

  1. Fig B demonstrates variation in female response to flash durations. These data represent an experimental manipulation of flash duration and female responsiveness to a range of flash durations. The results that female response is positively correlated with flash duration. This supports the hypothesis that females choose males based on flash duration.

 

  1. If spermataphore size is related to flash duration and longer flash duration elicits stronger response from females, then it is likely females are using flash duration as one means by which to assess male quality in terms of direct benefits to the female.

 

 

  1. Zahavi would say that flash duration is a reliable signal of spermataphore size. Zahavi would also say that for any signal (such as flash duration) to be honest, it must be costly. Only costly signals provide reliable information. Thus, Zahavi would say that flash duration must be costly. In this case, the energetic demands of producing the spermataphore is correlated with the energetic demands of producing the flash (it is also possible that flash duration increases predation risk). Thus the correlation between flash duration and spermataphore mass canÕt be faked and is therefore an honest and reliable signal that can be used by females to assess potential mates.

 

 

QUESTION E.  Does Figure 2 from Bates and Chappell (2002) show that cultural transmission can be maladaptive? Use the figure to explain the concept of cultural transmission and how Bates and Chappell tested the hypothesis that such learning can be maladaptive (what does maladaptive mean?) and how to interpret their results.

 

  1. Bates and Chappell tested the hypothesis that cultural transmission could result in a maladaptive behavior and prevent the learning of optimal behavior. Cultural transmission occurs when an individual learns a behavior from conspecifics. In this case the learning is horizontal (peer to peer). It is a form of imitative learning.

 

  1. They tested the hypothesis by training groups of guppies to take the less efficient route to food (the non-adaptive route).

 

This figure does show that a trait that would be maladaptive in an individual setting is performed in a group setting after cultural transmission.  Cultural transmission occurs when an individual learns a behavior from a conspecific individual.  This often happens through imitation.  Bates and Chappell tested the hypothesis that cultural transmission could result in a maladaptive behavior through their study of guppies.  First, they trained a group of guppies to take a longer than necessary path to food.  They then removed one trained individual and replaced it with an inexperienced guppy until they had treatment shoals with only guppies that had learned the route through horizontal learning.  They observed this guppy also learn the long path from the other trained guppies.  They then substituted another novice for a trained individual until the group was entirely novices trained only by their peers.  Cultural transmission often happens in this way, through imitation.  Figure 2. shows the results of an experiment where the peer trained guppies were introduced to a food source in a group and also individually.  When they were isolated, they lapsed back into the efficient, short path to the food.  However, when they were in the shoal, most of the guppies took the longer, seemingly maladaptive path to the food.  A maladaptive trait is one that decreases fitness for the individual, in this case it can be considered energy expended.  When the isolated guppies disregarded their culturally learned path to the food, it indicated that the performance of the maladaptive behavior is contingent on the environment.  The behavior could be maladaptive in that the guppies continued to perform the energy expending long path in the shoal tests.  However, we should then consider the possible adaptive characteristics of staying with the group.  Staying in the shoal could be beneficial to a guppy because it could reduce risk of predation.  When we consider these benefits, we see that the behavior is not actually maladaptive because of the benefits associated with group protection.