1. (20pts) Why are IQ heritability estimates for sibs raised in different households preferable to sibs raised in the same household? What additional confounding environmental factors are not removed from the heritability estimates of IQ?
The estimate for the IQ of sibs raised in the same household is confounded with the common rearing environment, while the IQ estimate for sibs raised in different households does not include such effects. However, any estimate of IQ based on sibs includes the confounding effects of the maternal womb environment which can explain up to 20% of the variation in "apparent heritability" (in the case of twins it is 20% for sequential sibs it is ~5%). It is desirable for our estimate of heritability to only include the additive genetic components of variation. Thus, any environmental effects will artificially inflate the true level of variation that arises from pure additive genetic causes.
It is technically not correct to raise the problem of dominance variation, which also confounds estimates of heritability for full sibs (though it does not confound estimates for half sibs). Dominance variation arises from a genetic cause. I asked for only the "confounding environmental factors" in the answer. Regurgitating everything that you know can hurt, as we deduct a few points for incorrectly mentioning dominance variation.
2. (20pts) After an artificial selection experiment on the frequency of wingbeats during the courting rituals in flies, you reach an upper plateau (graph the response to selection). Give two reasons why wingbeat frequency might not be able to continue increasing.
Marks are obtained for a correct graph!
i) Strong directional selection on any trait, in particular artificial selection, will deplete the amount of additive genetic variation (Va). As Va is depleted, the heritability for the trait will decline to zero and the evolutionary response to selection will likewise decline to zero and the selection plateau will be reached (according to the equation Response= heritability x selection differential). The line stops moving up or down when the heritability hits zero
[Note: another way to say this is that selection will rapidly fix all the high wing beat alleles in the high line and low wing beat alleles in the low line and when the additive genes are all fixed, the response to selection goes to zero].
ii) A second reason why selection response might reach a plateau has to do with the pleiotropic effect of selection for wing beat genes. Loci that control wing beat might also have a pleiotropic or correlated physiological effect on other traits that influence fitness. For example, high wing frequency might lead to a higher overall metabolism which has a shortening effect on lifespan. Such pleiotropic effects can also be referred to as trade-offs. At the plateau, the negative effects of pleiotropy on fitness exactly counterbalances the selective gains imposed for wing beat and an "evolutionary stalemate" is achieved.
3. (20pts) What is the appropriate level of selection to consider for behavioral traits and why? Pick the most appropriate level or levels and explain your choice with reference to examples.
This is one on my favorite questions -- you should have seen it coming.
Answer Tactic One. In theory if you argue well enough you could pick one level, dig in your heels and argue a good argument. The quality of any argument that picks a single level will be judged by the individual case. You must eliminate the other level of selection with reference to some counter argument to obtain full marks with the single level viewpoint.
OR
Answer Tactic Two. The easiest way to get full credit is to be "eclectic" and pick all levels. If this is your route, the easiest way to work in all levels is to illustrate how levels of selection "play-off" against one another. It is clear that individual selection (e.g., natural or sexual selection) is a sufficient explanation for most kinds of selection encountered in nature (it does require much more than an example to get full marks for individual selection). To understand the evolution of female choice for example, it is best to understand the joint evolution of male traits and their associated pleiotropic (correlated effects) on male survival. This amounts to a "whole organism" argument. However, genic selection is a valuable point of view to use when understanding kin selection, for example. The argument of kin selection is essentially a genic selection argument. If an individual engages in a self-sacrificial act, the net benefit is based on the total number of genes shared with kin regardless what the genes are!! --> A genic selection argument if I ever heard one. (Note: the above argument is the fastest way to validate genic and kin levels of selection. Many other more long-winded arguments about genic selection and kin selection could be used, but this argument integrates the need for both kin and gene perspectives in one feld-swoop). Finally, group selection is a theoretical possibility for the evolution of many behavioral traits. In particular, group selection allows us to explain why genic selection does not lead to higher levels of the "t-allele" in a population. There is a differential extinction of groups that get fixed for high levels of the t-allele (Another way to validate group selection perspective and genic selection is to take about genic selection, e.g., a cheater allele, that spreads in a population of "altruists").
4. (20pts) How are badges used in male contest? What are the advantages to the badge holder? How are badges used in female choice? What are the advantages to a choosy female? Why are such badges costly?
Badges are used in male-male contests to display physical prowess, and hopefully eliminate the need for the contest to escalate. This is a valuable time and energy saving mechanisms that allows males with badges to avoid conflict with individuals that have lesser prowess (any conflict has some probability of injury -- even between unequally matched combatants).
A female would use the badge to assess male quality. Because ESS models demonstrate that bluffing is not a viable strategy, a badge is typically an honest indicator of a male's genetic quality. Females indirectly benefit by passing on high quality genes to progeny.
Badges are costly precisely because they do require a honest "firepower" to back up the badge. Such physical prowess invariably is governed by genes, such as those that elevate testosterone, that have pleiotropic effects on other fitness traits like survival.
5. (20pts) What is the male's extended phenotype, and give an example of an experimental test of the role of the male's extended phenotype in affecting female choice? Why is it necessary to do such experiments? Describe two other male attributes that might be important for a female during mate choice and give a proximate and ultimate reason for each choice?
The extended phenotype includes all attributes of the male that are external to the males "bodily" phenotype, such as male territory quality. An experimental test is necessary to determine the role of male phenotype in female choice, because the female might be choosing a male for his territory quality (e.g., as it benefits the rearing of progeny), or the female might be choosing a male for the high quality genes that he is carrying that allowed him to takeover such a high quality territory.
Two other attributes that might be important for a female during mate choice, include other male sexual ornaments that might likewise be indicative of good genes. The good genes are the second attribute she is interested in. Many possible proximate and ultimate answers -- Just make biological sense when you construct them and you get full marks. For example: A proximate reason for the male ornament might be high T. An ultimate reason for the male ornament (e.g., red color) would be something selective such as success in sexual selection. A proximate reason for the female preference of good genes would be something sensory (such as sensory exploitation owing to female preference to red color. An ultimate reason for the female choice would be the indirect benefit of good genes for progeny.
Grading scheme for
Questions 5
Defining extended phenotype- 4 pnts
Giving an example of EXPERIMENTAL TEST- 4 pnts
Explaining WHY experiment was necessary- (showed what female what was selecting- extended phenotype or phenotype or good genes)- 4 pnts
Male attributes-
1 example of Phenotype with proximate and ultimate explanation for WHY FEMALE chooses (not male)- 4 pnts
GOOD GENES with proximate and ultimate reasons for female choice- 4 pnts
Partial credit was given for giving two examples of male phenotype
Because females are generally thought to invest more heavily in reproduction, they are typically involved in acquiring energy or providing care to young and thus are not available once fertilized. However, a single male can mate with multiple females. This leads to a biased operational sex ratio that leaves an excess of males. Males are selected for ornaments that make them more attractive to females so as to obtain more mates or males are selected for armaments that allow the males to win in male male competition.
The same reasons are true for sexual selection on female traits, except that males are now the limiting sex because they invest more heavily in progeny compared to females (e.g., brooding in male pipefish). (If you came up with some bizarre other reason that differed from the male argument you might have lost marks!!)
The ecological factors that promote monogamy relate to the ability of one sex to monopolize more than one mate. If the environmental quality is relatively poor, and food is not all that concentrated, then female territories will be dispersed at great distance. The distances are far too large for a single male to defend more than one female territory. The marginal gains from a very large territory size are negated by the lost paternity involved in trying to defend too many mates. QED the male becomes monogamous (Just an aside, though not required in the answer he is also much more likely to become paternal! or a caregive).
Question 6
Ecological factors leading to elaborate male traits- Females invest more in parental care- making them choosier, becoming the limited sex- resulting in Male biased sex ratio - excess males- 7 pnts
Ecological factors leading to elaborate female traits- reverse of above- 6 pnts
Ecological factors promoting monogamy- resources and mates are rare/highly dispersed, difficult to defend multiple mates- 7 pnts
Partial credit for costs of parental care.
7. (20pts) What are the two critical conditions for sympatric speciation? Apply these two principles to the problem of "deme recognition" in bird song and song learning.
The two critical conditions for sympatric speciation are selection for assortative mating (like mates with like) largely because hybrid progeny (like mating with non-like) are less fit than matings among similar types. Or the flip side argument is just fine: also Hybrid unfitness selects against animals that do not mate assortatively, which leads to positive assortative mating.
"Deme recognition" in female birds is selected because of "outbreeding depression". Outbreeding depression (e.g., synonymous with hybrid unfitness) arises from matings between birds of such dissimilar genetic stock that genes do not function well together (e.g., epistasis). A female bird that learns its father song as a chick is likely to prefer such songs when they mature. The prior exposure to fathers song making the female more likely to mate with an individual of similar genetic background.
8. (20pts) Describe the central assumption underlying optimal foraging theory. Describe how learning as a cognitive process, and memory as a cognitive process limit the solutions that animals can come up with from the point of view of optimal foraging?
The central assumption of foraging theory is that energy is in someday positively related to fitness, and thus maximizing or optimizing energy will lead to a foraging strategy that maximizes fitness.
Another implicit assumption of foraging theory is that animals are all knowing or omniscient. An animal that must first learn where food is or how to get at food cannot be foraging optimally (yet). Another cognitive constraint on foraging is that an animal can keep track of all items necessary to come up with the correct foraging decision. For example, a bee foraging on flowers that are variable in reward cannot come to the correct decision if it can only remember the last flower that it visited. In order to come up to a correct decision, the bee must be capable of remembering the last few flowers.
You must have stated both assumptions of optimal foraging for full marks!