Exam 2 KEY: drawn from student answers

 

Section I

Question A - Optimality

a)    This means that an animal makes decisions that will improve its fitness.  These decisions are based on a cost benefit analysis on which behaviors will prove most beneficial to the organism based on maximizing benefit and minimizing cost. OR An animal behaves optimally if the behavior yields the maximal net benefits given the conditions and if fitness and reproductive success is maximized. It is assumed that an optimal behavior is a product of natural selection, because natural selection will increase fitness.

b)   An optimality model is a mathematical model that uses optimization theory to make predictions about why a behavior occurred. These optimality models are hypothesis-tentative explanations for behavior that make predictions within a set of constraints, assume natural selection optimizes behavior, and are as simple as possible. OR An optimality model is a model that uses mathematical analysis (optimization theory) to predict various facets of animal behavior within a designated set of restraints.  These models use a cost/benefit analysis to predict the probability of an organismÕs behavior, given specific parameters, in order to maximize its fitness.

c)    In order to construct an optimality model, first, the possible behaviors (based on the animalÕs natural history) must be specified and limited by constraints. Next, a currency is chosen, which is what will be optimized/maximized. It is important to note that the currency must have a fitness consequence or have something to do with fitness even if fitness cannot be measured directly. Then, the cost and benefits must be determined, meaning the relationship between behaviors and the currency must be delineated. Finally, a model can be created that specifies this aforementioned relationship (how behaviors relate to currency, which show tradeoffs) and determines the highest net return for all behaviors. Methods for testing models include running time budgets, from the dung beetle example in class, and using differential calculus to determine optimal time based on the point of intersection of the tangent line (and various mathematical modes can be applied where appropriate). It is then possible to use this model to make predictions and attempt to explain why a behavior occurred.

d)   The possible behaviors include foraging for ÔAÕ (25 cal. nuts that require 2 minutes to open) or foraging for ÔBÕ (15 cal. nuts that require 1 minute to open). The currency will be defined as Energy/Time or (Calories per nut/Minutes required to open nut). The costs and benefits are as follows: the higher caloric content nut (A) gives more energy but takes up valuable time that the chickadee could be using to gain more calories from other food sources, and the lower calorie nut (B) gives less energy back to the chickadee but also requires less effort and allows more time for the chickadee to forage for other food/calorie sources. When each behavior is examined based on the energy it provides per the amount of time spent acquiring the energy, foraging for A yields 12.5 calories/minute spent opening the nut (25cal/2min) while foraging for B yields 15 calories/minute spent opening the nut. Based on the costs and benefits and the currency we can conclude that the optimal behavior is to forage for B because it yields higher net benefits for the chickadee. For example, if the bird spends two minutes opening nuts, it will gain 25 calories from ÔAÕ (because it will only be able to open one nut) but it will gain 30 calories from ÔBÕ (because it will have opened two nuts, with 15 calories each). Thus foraging for ÔBÕ will, in the long run, give the chickadee much more calories than it would gain from foraging for ÔAÕ in the same amount of time, making it a more efficient source of energy as well as the optimal behavior.

 

Question Bmating system

a)    Both parental effort and mating effort contribute to male fitness; mating effort increases the likelihood that the male will produce offspring, and parental effort increases the likelihood that the offspring of the male will survive (assuming that the male provides benefits to the offspring, such as protection or food). The trade-off lies in the balance that the male makes between these two options: to optimize his reproductive success, the male needs to balance producing the maximal number of offspring that will receive adequate care to survive. In the example above, the Prarie Grouse is able to put in no parental effort because itÕs investing all of its time in mating effort (energy into sperm production and competition for as many mates as possible), whereas LeachÕs storm-petrels invest their time in cooperative parental care, putting less energy into mating effort because theyÕre investing so much more energy in the success of their offspring.

b)   There is a difference in the sexes because females in these scenarios are putting all of their energy into forming eggs and providing parental care. [Female reproductive success is limited by resources needed to produce offspring, whereas male reproductive success is limited by access to mates.]

c)    Grouse

d)   d.1) Praire Grouse

e)    d.2) Male

f)     d.3) The male Prairie Grouse is more likely to have extravagant traits due to the fact that itÕs putting all of its energy into mating effort. If the maleÕs only contribution to the femaleÕs reproductive success is his sperm, sheÕs selecting him purely on the basis that the traits that he displays are (hopefully) honest signals regarding the quality of his genes. In order to display his genetic superiority, the male Prairie Grouse must have a way to show his caliber, usually through extravagant traits. Female Prairie Grouses would not display extravagant traits because she is putting in all of the parental effort, and not wasting any energy on unnecessary physical traits that are potentially costly to maintain. The Storm-Petrel, on the other hand, is less likely to show extravagant traits in either sex because the male and female are contributing equal amounts of energy to parenting, indicating that the males are less likely to spend their energy on extravagant traits like the Prairie Grouses. 

 

Section II

Question B - fireflies

a)    a) The figure on the left is illustrating the relationship between flash duration (msec) and the spermatophore mass (mg) of male fireflies. Based on these data, Cratsley and Lewis concluded that flash duration was the single best predictor of spermatophore mass, and it appears that longer flash duration correlates with a larger spermatophore mass. This relationship is an example of honest signaling because flash duration is a trait that demonstrates the malesÕ quality, which is spermatophore size in this case. Female fireflies will choose males with longer flash durations in order to obtain a larger spermatophore mass because spermatophore provides all the nutrients for a female, therefore they will select larger ones. The trait of flash duration is also an honest signal because it bears a cost with it. Though it will attract females due to the likely presence of a larger spermatophore, males with longer flash duration are more vulnerable to predators and they have to allocate more energy to a longer flash duration (and a larger spermatophore). Due to the fact that there are direct costs to males with this trait, and that it is a direct indicator of male quality, flash duration can be considered an honest signal.

b)   b) The figure on the left illustrates the relationship between simulated flash duration (msec) and female response (%). Male fireflies are competing for female mates, and certain male courtship traits (in this case, flash duration) have an influence on female mating preference. As shown above in the graph on the left, flash duration predicts spermatophore mass, and longer flash duration usually indicates a larger spermatophore. Spermatophore mass is an example of a nuptial gift, or a nutritious resource that aid females in their reproductive effort of generating offspring. It is logical that females prefer/select for a larger spermatophore because it will provide more nutrients. Thus, if flash duration predicts spermatophore size, females should choose males with longer flash duration more often, which is what is being shown in the figure, where increased flash duration elicits increased female response. Therefore, this figure illustrates female choice of these fireflies, because they are selecting for the more attractive mates (with better nuptial gifts) based on the honest signal of flash duration.

c)    c) These figures illustrate sexual selection in fireflies. Specifically they depict how male fireflies compete for female mate selection using honest signaling of flash duration to indicate quality (spermatophore size). ZahaviÕs Handicap Principle states that all signals that indicate male quality are honest and that any signal a male uses to attract a female has to have a cost, and if its not costly then its not honest (because fake isnÕt evolutionary advantageous). Therefore, based on this principle, flash duration is an honest signal of male quality, or spermatophore size, because it directly correlates with spermatophore size and comes with several costs (increased predation risk, increased energy investment, etc.). These graphs serve to illustrate this honest signal and how it affects female response.

 

Question C – cultural transmission

d)   The transfer of information from individual to individual through social learning or teaching. [It can be either vertical or horizontal and can, therefore a behavior can come become common within a population much more rapidly than through natural selection directly on that behavior).

e)    It increases the fitness of the animal compared to an alternative behavior.

f)     It decreases the fitness of the animal compared to an alternative behavior.

g)    Social learning of foraging behavior does not inhibit learning of optimal behavior, but that trade-offs occur when tested in group conditions.

h)   That the hypothesis was correct and therefore the social learning of foraging behavior does not inhibit learning of optimal behavior, but that trade-offs occur when tested in group conditions. The figure shows this because the experimental group almost always followed the learnt behavior of taking the longer route when in a group, but not when isolated, while the control group that was not subjected to social learning always chose the shorter route. The fact that the experimental group always took the longer route in the shoal suggests that there is an advantage of traveling in a group rather than alone, since when an individual in the experimental group was isolated it mostly took the shorter route. On the other hand, the control group always maximized their fitness by always taking the short route regardless of if they were isolated or in a group.

In conclusion, the benefit of traveling in a group is much higher than the benefit of taking a shorter route. The learnt behavior of taking the longer route is only maladaptive when traveling in groups since the guppies in the experimental group always took the long route while they could have benefited more by taking the short route.

 

Section III

Question D - learning

a)    Classical conditioning involves two stimuli, the unconditional stimulus (which is a releaser that elicits a fixed a fixed action pattern response, or one that occurs without other training/learning) and the conditional stimulus (which initially has no effect, but eventually elicits the learned behavior after having been associated with the unconditional stimulus). In Classical Conditioning, the researcher introduces another stimulus and replaces the unconditional stimulus with something that is unrelated. It is important to note that the response sometimes depends on when the stimuli are introduced in relation to each other. A famous example of Classical Conditioning is PavlovÕs experiment with dogs, where dogs were conditioned to salivate (conditional response) when shown a light (the conditional stimulus) using meat powder (unconditional stimulus) that, alone, normally generates salivation as a response (unconditional response).

b)   Operant Conditioning, also known as Instrumental learning [or Òtrial and errorÓ learning], occurs when the animal learns to associate a behavior with the consequences of the behavior, thus the behavior is reinforced with either positive or negative consequences. A behavior that is rewarded should increase with positive reinforcement. A famous example of Operant Conditioning is the Skinner Box, which rewards a rat with food only if the rat can successfully press the lever (a mechanism that animals can manipulate to receive reinforcement) therefore they learn quickly. 

c)    The main difference between these two types of learning is the type of behaviors these are based on; Classical Conditioning is based on involuntary behavior [the experimenter is in control] while Operant Conditioning is based on voluntary behavior [the animal is in control].

d)   Operant Conditioning

e)    Operant Conditioning is more likely to occur in nature than Classical Conditioning because in the wild it relates to how animals deal with their environment in a relative way or a way that increases their fitness and probability of reproductive success. Classical Conditioning typically only occurs in experimental conditions because the environment and stimuli must be carefully controlled. Also Classical Conditioning uses a foreign or unknown stimulus that doesnÕt normally elicit a response (conditional response), which would not occur in nature. Under Operant Conditioning animals to use trial and error to test behaviors to find the most positive consequences, allowing them to essentially optimize their behavior to obtain positive feedback.

 

Question E – sexual selection

a)    For natural selection to occur, there must be variable, heritable fitness. There must be individual variation in a trait/different forms of a trait in the population. That trait must have a heritable component as a means to pass it on to future generations. There also must be fitness consequences of the trait - differential reproductive and mating success based on the variation in the trait.

b)   Sexual selection is similar to natural selection because for both, there must be variable, heritable traits in a population.  Both processes select for certain traits that are varied and heritable, and are typically the ÒbestÓ variations in a population.  Individuals with those Òfavorable,Ó advantageous traits pass those traits on to future generations, increasing the frequency of the trait in a population over time.

c)    In natural selection, traits conferring the highest fitness (in terms of survival and reproductive success) in a certain environment are passed on and increase in frequency over time. However, with sexual selection, traits that confer the highest reproductive success – ability to attain or choose a mate - are passed on, instead of traits that also influence or favor an individualÕs ability to survive.  So, sexual selection is more specific than natural selection in that it selects for/enhances traits that solely confer mating and reproductive advantages on its possessor.  Sexual selection does not adapt the individual to the specific environment as natural selection does because it is powerful enough to keep certain traits in population even though they are maladaptive, costly, and harmful to the individualÕs survival. 

 

Question F - spiders

a)    By the male redback spider allowing the female to devoured itself, the male is offering the female a nuptial gift in the form of a food source. A way to test whether this action is an adaptive action for the redback spiders would be to test whether this action increases the fitness of the spiders or not. We would have a control group that continued their usual action and there would be an experimental group that separated the males and females before the males could be consumed. We would measure the number of offspring that survived for the two groups.

 

a.     Ho = more of the offspring from the male that was consumed will survive.

b.     Ha = more of the offspring from the male that was not consumed will survive.

c.      Hn = the same number of offspring will survive in the experimental group and control group.

 

b)   A male can only mate once if he is eaten during copulation. If a male escapes and does not do a back flip, then he can go on and reproduce with another female. To support the hypothesis that this is a maladaptive behavior, researchers should count the total number of offspring produced by a consumed male and an escaped male. The male that is eaten will only produce offspring with that one female, which would potentially be less than the number of offspring produced by the male that escapes who mates with multiple female spiders.

 

Question G - testosterone

The answer is in the tradeoff between survival and reproduction.  Natural selection is more than an organismÕs ability to survive; variable heritable fitness deals with both survival and reproduction.  For testosterone to persist while reducing the survivability of male mammals, it must provide some alternative benefit to the organismÕs fitness.  For example, testosterone has been found to increase male aggressiveness and sex-drive.  These behavioral changes may increase a maleÕs fitness, and even if it does not survive to participate in as many reproductive cycles as males with no testosterone or modified testosterone, it may find greater success over other males in the reproductive cycles in which it does participate.  If the benefit of its increased reproductive success outweighs the costs of its reduced survivability, then males with high testosterone levels possess greater fitness and will be selected for.  If conditions changed such that survival was valued more than sexual fitness [i.e., the ability to obtain mates], or if a mutant were able to produce a chemical with the benefits of testosterone without its costs, then natural selection may lead to the elimination of testosterone.  Otherwise, it is here to stay.