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.
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.
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.