Midterm Answer Key:

 

1. What are the four questions that Tinbergen asked about behavior? First, explain the gist of each question. Then, explain each question in terms of ultimate or proximate causes.

4 pts each for the gist:

  1. Causation refers to the proximate causes of behavior such as the hormones, genes, nerve impulses that control the expression of behaviors.
  2. Development refers to the ontogeny of behaviors such as imprinting, or in the case of cognition, issues of learning.
  3. Evolution refers to the phylogenetic context in which the behaviors are found. For example, the prevalence of parental care in birds, but not reptiles (with some exceptions) is an example of the taxonomic affiliations of some behaviors.
  4. Function refers to the adaptive value or contribution that the behavior makes to fitness.

 

4pts (1 pt each if the answer is placed in the above answer): Some set of sentences that says a few of the following points: Causation in Tinbergen's view is concerned with Proximate Causation or mechanism. Development is also considered to be in the category of proximate cause. However, evolution or phylogenetic context is squarely in the field of ultimate cause, as is the issue of function as such issues of adaptive value or fitness are directly related to evolution and evolutionary change. Our study of animal behavior begins with a consideration of the ultimate causes of evolutionary change -- adaptation and natural selection.



2. You overhear someone in the coffee shop citing the following evidence regarding heritability of IQ: "IQ must be very heritable, the correlation between fraternal twins reared in the same household is 0.58." Hah!" the other combatant exclaims, "The correlation between an adopted child and their unrelated sib is 0.29, which suggests that correlations for IQ based on familial correlations are flawed. How can you get a positive correlation between unrelated individuals?"

Who is right? Explain the biological source of both these correlations?

Well, they are both right, but why?

5pts: Fraternal twins do share common genes. On average, they should share 0.5 due to genetic causes, if IQ was only caused by genes. This places an upper limit on how much they should have in common due to genetic causes. The actual genetic causes are also influenced by how strong the genetic factors are -- or the heritability. Thus, should probably be adjusted down because it assumes that genes influence everything in IQ.

5pts: The actual correlation, 0.58, is much higher than this theoretical maximum because fraternal twins also share a common womb environment which might inflate their resemblance and because they are reared at the same time in a common household environment. Thus, the effects of common environment inflates their resemblance.

5pts: Two unrelated individuals share only a common environment. They do not share genes. The correlation of 0.29 for an adopted child and their unrelated sib must be largely due to the common effects of rearing environment.

5pts: Thus, the correlation seen in Fraternal twins reared in the same family probably includes a genetic component and an evironmental component.


3. a) Explain sex determination in hymenoptera. What is special about male sperm in hymenoptera? b) Why are social hymenoptera predisposed to "altruism" more so than most other organisms? Your argument in part b) should be based on a discussion of relatedness of members of the hive, and Hamilton's ideas on kin selection (verbal argument or explanation with words and equations for Hamilton's idea are OK).

4pts: Sex determination in the hymenoptera is governed by ploidy (n or 2n):

1.eggs that are fertilized develops into a female (2n),

2.eggs that are unfertilized develops into a male (n),

4pts: Haplodiploidy, leads to some high coefficients of relatedness for females and males. A key observation is that males produce genetically identical sperm.

4pts: Thus if a foundress (a founding queen) for a hive is fertilized by a single male, the daughters from such a union share 0.75 of their genes on average which is considerably higher than the typical 0.50 shared by sibs. Why? The daughters get the usual 0.25 resemblance from mom and 0.50 from the father. Thus sisters (worker and queen) share 0.75 of their genes, far higher than normal.

4pts: In contrast, a normal organism gets 0.25 from mom and 0.25 from dad to total 0.50.

4pts: verbal argument: Hamilton has argued that such a high coefficient of relatedness predisposes the hymenoptera to the evolution of kin based altruism. In Hamilton's equation, the relatedness is far higher for hymenoptera, thus the inclusive fitness an individual receives from an altruistic act is far higher than normal (0.75 vs 0.50), which makes it likelier that altruism will evolve. OR description of equation:

W = d + sum(i * r), if d, the direct effect is deleterious to the invidual, then it is a fitness cost. The indirect costs, i should be a fitness benefit to kin for the system to evolve the behavior. Because r is higher for hymenoptera (0.75 vs 0.50), the inclusive fitness, d + i*r, is higher for a similar cost (d).


4. Define premating and postmating isolating mechanisms. Why do behavioral isolation mechanisms between species evolve? Isn't sterility enough to keep species from mixing?

Make some kind of distinction between (do not need all the kinds listed):

5pts: A) Premating isolating mechanisms -- prevent union of gametes -> zygote

1.mates do not meet (seasonal or habitat isolation)

2.mates meet but do not mate (ethological or behavioral isolation)

3.mates meet but no sperm transfer (mechanical isolation)

5pts: B) Post-mating isolating mechanisms -- varying degrees of hybrid sterility

1.sperm transfered but dies before fertilization

2.zygote dies

3.zygote produces an F1 adult that has reduced viability (survival)

4.hybrid is viable, but partially or completely sterile (fecundity) or the F2 is deficient.

10pts: The answer hinges on addressing the following somewhere in your answer: Which of the two mating isolation mechanisms is the most effective in reducing the risk of producing low fitness offspring? Which mechanisms is most efficient in terms of time and lost reproductive opportunity?

For example, this is a suitable answer: An organism that mates with a different "semispecies" might produce low viability offspring (in any of the degrees listed above) and such a individual has lower fitness compared to an organism that discriminates against such semispecies and mates with members of its own semispecies (e.g., posseses isolating mechanism A.1, A.2, or A.3 or perhaps all of the above discrimination mechanisms). Such behavioral descrimination ability should evolve rapidly in the area of incipient speciation, under the right conditions.


5. a) The war of attrition suggests that males should not display information or intentions during contests because it could be used by the other contestant against the male. Should a male wear a badge during symmetric or asymmetric contests? b) What are the advantages of wearing a badge of status? Make sure your answer addresses the following points: c) the role of badges in male-male contests and b) the role of badges in models of female choice.

4pts: The war of attrition considers symmetrical contests and combatants should not display information. However, in the case of asymmetric contests, a superior individual should display information.

8pts: In asymmetric contests a male mating type which is stronger than the others would be expected to "advertise" this skill by some sort of badge of status. By walking around and displaying this badge of status, a very dominant individual could avoid most contests because other males would be unlikely to challenge such a powerful or skillful male. By avoiding unecessary contests the dominant individual could focus on contests with other more equally matched individuals that are likely to lead to a War of Attrition. Some advertising may be necessary on the part of the most dominant individuals even though the simple war of attrition models suggest otherwise, because the dominant can avoid many contests.

8pts: Good genes models contend that a female chooses males on the basis of elaborate ornaments because such ornaments are strong indicators of the superiority of the male's genotype for genes unrelated to the trait. Presumably, a male with an elaborate male trait, such as a badge would have to be quite superior to be able to survive to reproductive age with the large trait and thus he should have many genes that are related to his overall vigor, that are unrelated to ornament per se. Badges are thought to be honest advertisement of a male's vigor in male-male contests and thus should be related to his overall genetic quality.


6.a) What are two assumptions of the model of runaway sexual selection? b) What is the key prediction of the theory of sexual selection by runaway process? Briefly, describe evidence supporting the key prediction. c) How do the runaway process assumptions differ from indicator models of female choice? d)What are the benefits to the female for each model of sexual selection?

4pts: Runaway assumes that females preference is genetically based. The male trait is also genetically based.

4pts: Given that this is true the males with elaborate traits are chosen by choosy females and female choosiness and the elaborate trait become genetically correlated in subsequent generations.

4pts: A breeding study reveals evidence of this correlation. Daughters from the same sire show choosiness and their brothers show the elaborate trait. Thus, we infer that the genes for choosiness and the elaborate male trait were both passed on from the father.

4pts: Indicator models do not rely on the elaborate male trait being due to genetics differences in trait size. The size of the male trait could be a physiological indicator of the males vigor, he can grow a large tail because he has lots of resources. Variation in the indicator trait does not have to be genetic, it just should indicate the males physiological vigor or other measure of male quality.

4pts: In some sense, the benefit that the female gets in runaway is that she will produce sexy sons. The benefits for the female in indicator models are that she will produce healthier or genetically superior offspring.


7.a) Describe the marginal value theorem in terms of a male bird that is faced with the "decision" of mongamy versus polygyny. b) Provide at least three trade-offs that the male must consider when adopting a monogamous vs polygynous lifestyle.

8pts: The marginal value theorem yields the "giving up time" or when an organism should leave a patch that it is exploiting. Consider the territory of a monogamous male versus polygynous male. As an animal begins defending a small versus large territory, its fitness depends on how many females it gets, but whether or not it truly can defend the females and be certain he sires the offspring. His choice defend a small territory or try to work a large territory.

Females may be so widely distributed that males cannot monopolize more than one

female.

4pts for each, only need 3 of the following 4:

  1. In such cases, searching for another mate may be very costly. Think back on the marginal value theorem and how it would apply to mate search.
  2. If the female is occupied with another male, the costs of usurping control of the territory may be so prohibitive given that resident males have a strong home-field advantage, that it would pay for a male to remain with a single mate.
  3. In addition, if the male were to abandon the female, she is very likely to mate again with a rival male. A male may enter into a monogamous relationship to mate guard the female.
  4. Finally, a it might pay to remain at the nest, participate in rearing the young, because this enhances the male's fitness more than moving on to find other mates.


8. What are aposematic signals? Describe Fisher's theory for the evolution of aposematic signals in terms of Hamilton's ideas for kin selection and inclusive fitness (again a verbal argument may be as good as one that makes direct reference to Hamilton's equation).

4pts: Aposematic signals are bright colors or loud noises that warn/advertise a predator of the signaller's danger or toxicity.

16pts with the following breakdown: verbal: Ronald Fisher observed that many aposematic forms tend to also be quite gregarious and congregate in the same locale (4pts).

Fisher speculated that kin selection may favor such aggregations. An individual may die during the learning required to teach a naive predator that the color also results in a bad experience (4pts).

However, because the predator leaves the remaining kin alone, the inclusive fitness of the dead aposematling is positive because the cost of individual death is balanced by the surviving kin that are left alone (4pt).

Gregariousness can easily result from kin groups (4pts) (e.g., a localized clutch), and such kin groups greatly enhance the probability that aposematic coloration will spread even though brightly colored individuals attract attentions of naive predators.

OR equation argument:

16pts: W = d + sum(i * r), if d, the direct effect is deleterious to the invidual (i.e., eaten=dead=-1), then it is a fitness cost. The indirect costs, i should be a fitness benefit to kin for the system to evolve the behavior. Because r is 0.50 (assuming sibs), the inclusive fitness, d + sum(i*r), is high because the sum is summed across all the aggregated sibs. If there are a lot of sibs, then W can be quite high.