1.1 The monogamous prairie vole Monogamous (prairie vole) versus Polygynous (all others -- ex. meadow vole) WHY?
1.2 The brain of the prairie vole is a complex, highly organized machine Vasopressin - large number of receptors (V1a) in Ventral pallium - (emotion and memory) Copulation --> some brain areas release large amounts of vasopressin --> binds to pallium vasopressin receptors --> rewards animal
1.7 Testing the hypothesis that monogamy in prairie voles is linked to a specific gene Meadow voles!!! Gene in two different brain areas
1.3 A gene that affects male pairing behavior in the prairie vole
Box 1.1 How are phylogenetic trees constructed and what do they mean?
1.4 The evolutionary relationships of the prairie vole and six of its relatives
1.5 The possible history behind monogamy in the prairie vole
Which is correct? Brain physiology? Specific genes that up-regulate hormones? Up-regulation of receptors? Reproductive benefits by guarding females?
All answers could be correct BUT Levels of analysis very important mutant gene changes behavior male remains with female and prevents her from mating with other males leads to greater reproductive success and survival (less infanticide) genetic makeup changed Example. Gene for vasopressin receptor protein increases
1.6 The connection between evolutionary history and the mechanisms of behavior
The great behavioral biologist Niko Tinbergen said that there were four main questions for behavioral researchers How does the behavior promote an animal’s ability to survive and reproduce? How does an animal use its sensory and motor abilities to activate and modify its behavior patterns? How does an animal’s behavior change during its growth, especially in response to the experiences that it has while maturing? How does an animal’s behavior compare with that of other closely related species, and what does this tell us about the origins of its behavior and the changes that have occurred during the history of the species?
Question 1 deals with issues of adaptive value (ultimate/evolutionary); Question 2 focuses on the physiological level of analysis (proximate/immediate); Question 3 has to do with developmental causes of behavior (proximate/immediate), while Question 4 deals with the historical origins and modification of behavior (ultimate/evolutionary). Although ultimate sounds more important than proximate, both levels of analysis are essential for a complete understanding of behavior; ultimate analyses complement proximate ones, and vice versa; a total understanding of the ultimate causes of behavior would still leave a huge explanatory gap that could only be filled by information on the immediate causes of behavior.
Example: When a female baboon copulates, she vocalizes loudly, but her cries are longer and louder if her partner happens to be a high-ranking “alpha” male. A primate researcher has suggested that females cry out more vigorously when copulating with top males because this warns low-ranking baboons to stay clear. (Subordinate males sometimes harass mating pairs to such an extent that the copulation ends prematurely, but if that happens, they may be attacked by the dominant male whose mating has been so rudely interrupted.) The same researcher also says, however, that the more vigorous cries may simply reflect the fact that females are more strongly stimulated by the larger, more energetic, alpha males. Are the two explanations really in competition with each other? Explain why they could both be right and how they could be shown to be complementary.
What we have here is a dispute based on thinking that proximate and ultimate explanations are in competition when in fact they are complementary. The proximate cause of the female’s loud calls could be related to the nature of stimulation provided by a dominant male; the adaptive consequence of giving those calls in response to that stimulation could be a reduction in interference from subordinate harassers (leading to greater reproductive success)
1.4 Imagine that it would be possible to inject prairie voles with a chemical that tied up the V1-a receptors in the ventral pallium. If that experiment were done, what outcome would result in the rejection of the vasopressin receptor hypothesis for monogamy in the prairie vole? Which is better, a tested hypothesis that is rejected, or a tested hypothesis that is accepted?
The vasopressin receptor hypothesis yields the prediction that if these receptors were blocked, then the intense social bonding that normally occurs between males and their sexual partners would not occur. If it did occur, then the hypothesis would have to be rejected. Although human psychology being what it is, we tend to think that accepted hypotheses are somehow superior to ideas that have to be thrown out, nevertheless, science advances whenever a hypothesis is adequately tested no matter whether the outcome is the rejection or acceptance of the explanation.
Statistical Analyses involve two competing hypotheses: a null hypothesis and an alternative hypothesis. • A null hypothesis is an explicit claim about the value of a specific parameter. • Example:What would you predict if the decision to turn left/right on the T-maze is random? • In our example, the probability to turn right P(R) must equal the probability of the subject turning left P(L). Because subjects have two mutually exclusive choices at the decision point we know that the probability of turning either left or right P(R or L) = P(R) + P(L) = 1, or P(R) = P(L) = 0.5. Thus, we can make an explicit claim about the probability that a subject turns right or left at the decision point. Our null hypothesis is that P(R) = 0.5 (or, equivalently, that P(L) = 0.5).
Our alternative hypothesis simply states that our null hypothesis is not true, that P(R) = P(L) ≠ 0.5. Every statistical test involves the computation of a test statistic. A comparison of the test statistic to a critical value allows us to either accept our null hypothesis or reject our null hypothesis in favor of the alternative hypothesis. We accept the null hypothesis if our test statistic does not exceed the critical value and we reject the null hypothesis in favor of the alternative if the test statistic exceeds the critical value.
"When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the state of science" -- William Thomson Kelvin
Scientific Method Initial Observation Phrase a Question Phrase Null and Alternate Hypotheses Plan Experiment that distinguishes between the two hypotheses Conduct Experiment in Double-Blind Fashion Un-blind samples Analyze Data (Get numbers!) Statistical tests Reject Ho? Draw Conclusions Communicate Results
1.5 Take the material in the paragraph on page 5 of the textbook in which work by Larry Young’s team on the V1aR gene hypothesis for prairie vole monogamy is described. Rewrite this material so that you present a single sentence each for the question about a cause that motivated the research, the hypothesis about what the cause was, a prediction that was derived from the hypothesis, the test evidence that was gathered to check the prediction, and the conclusion that the researchers accepted on the basis of their research.
1.7 Imagine that a mutation occurs this year in the gene that codes for the V1-a receptor protein in prairie voles. The altered protein increases the tendency of a male to form social bonds with a mate, in effect making him somewhat more monogamous than the typical male prairie vole. What is required if enhanced monogamy is to become more common in this species over time? If monogamous males have 3.7 pups on average during their lifetime while enhanced monogamous males have 4.1 on average, will the allele associated with enhanced monogamy necessarily make up an increasing proportion of the population? (“No” is the correct answer. Why? Hint: How does natural selection “measure” individual reproductive success?) Now imagine two types of prairie voles, one type that usually lives for 1.5 years and another for 0.8 years. Would it ever be possible for the one that died sooner to replace the longer-lived type over time?
Any change in monogamous behavior will spread only if individuals carrying the altered gene that influences the development of their behavior have more surviving offspring than others with a different hereditary basis for their behavior. The number of babies individuals have is not necessarily an indicator of the number of surviving offspring they will have, which is why males with 4.1 babies on average will not necessarily leave more copies of their alleles than males with 3.7 babies on average.
Male Hanuman langurs apparently use a rule of thumb when deciding which infants to kill: they attack youngsters of females that they did not copulate with prior to the birth of those offspring. In light of this finding, some observers have an explanation for why it is that after a takeover pregnant females may mate with newcomers. These researchers have suggested that the females’ behavior may create confusion about the paternity of their babies, the better to limit male infanticidal behavior. If females also engage in paternity confusion when their band contains several adult males, what predictions can you make about (1) the duration of female receptivity each reproductive cycle, (2) the relationship between the period when females are in heat and the timing of ovulation, and (3) the occurrence of copulations by subordinate males as well as the dominant male langur, who attempts to monopolize sexual access to the female?
If the paternity confusion hypothesis is correct, female receptivity should last longer than the period in which egg fertilization can occur. Ovulation and estrus need not be closely correlated. Subordinate males should succeed in copulating with females, although not necessarily when ovulation is actually taking place.
1.11 In an assassin bug, a predatory insect, males stand guard over clutches of eggs that females (usually their mates) have laid on leaves. The males protect the clutch against parasitic wasps that attempt to lay their eggs in assassin bug eggs. From time to time, a male stabs one of the eggs in his clutch with his beak, injecting it with digestive enzymes before drawing out the fluid. Needless to say, this act destroys the egg and so constitutes a kind of infanticide. If infanticide of this sort has evolved through sexual competition for quicker reproduction, as in Hanuman langurs and lions, how should males treat clutches laid by their copulatory partners versus those that the males “adopted” when they forced another male to leave an egg mass he had fertilized, something that happens occasionally? Once you have a prediction in hand, consider these two findings: (1) the parentage of the eggs has no effect on the number eaten, which increases steadily as the period of egg guarding lengthens, and (2) males do not lose weight while egg guarding, even though they cannot feed elsewhere. Are these findings relevant for the quicker reproduction hypothesis? Do they support another hypothesis for the tendency of males to eat some of the eggs under their care?
The prediction is that males should tend to destroy the eggs fertilized by other individuals rather than consuming the eggs they have fertilized themselves. However, the failure of males to discriminate against eggs fertilized by other males suggests that sexual competition is not responsible for the fact that males destroy some eggs under their care. Instead, it appears that males eat some eggs in order to maintain body condition during the long period when they are forced to remain close to the brood they are guarding.
1.13 Variation in suicidal tendencies in a make-believe lemming-like species Group Selection
Lemmings are small rodents that live in the Arctic tundra. Their populations fluctuate wildly. At high population densities, large numbers leave their homes and travel long distances, during which time many die, some by drowning as they attempt to cross rivers and lakes. One popular explanation for their behavior is that the travelers are actually committing suicide to relieve overpopulation. By heading off to die, the suicidal lemmings leave shelter and food for those who have stayed behind. These surviving individuals will perpetuate their species, saving it from extinction. What theory was used to produce this hypothesis? How would George C. Williams use Gary Larson’s cartoon (Figure 1.13 of the textbook) to evaluate the hypothesis critically?
The idea that lemmings commit suicide to help their species as a whole is based on group selection theory. The problem is that suicidal individuals are said to die to help others, which should have the result of eliminating any distinctive allelespossessed by the suicidal types. In short order, only individuals that did not commit suicide at high population densities would be left and their alleles would predominate in the population. Natural selection typically trumps group selection in causing evolutionary change to occur.
1.10 Natural selection Differential reproduction and survival
Summary Causes of any behavior can be understood in terms of four different levels of analysis; 1) how the behavior develops; 2) how the physiological mechanisms make behavior possible; 3) how the behavior promotes the animal’ reproductive success and 4) how behavior originated and has changed over evolutionary time. Four levels can be condensed into two (proximate and ultimate causes of behavior). Proximate and ultimate causes are interrelated. Genes present in animal today reflect adaptations over time and exert proximate influences over course of individual’s development allowing it to do certain things. Begin with a question about what causes an animal to do or exhibit a particular behavior; we devise a testable null hypotheses to answer the question; we design an experiment and collect data; if results differ from null we reject Ho and we accept the alternative hypothesis.