PSY 252H - Introduction to Animal Behaviour

ANSWERS FOR THE SECOND TERM TEST SPRING 1997

1. Name and briefly describe the four main types of social (labour) parasitism in ants. (3 points for each part)

Type 1: Guest ants build there nests near host-species colonies and steal food by soliciting returning host-species foragers.

Type 2: Temporary parasites are species whose queens found colonies parasitically by entering a host species nest, displacing the host-species queen, and inducing the host-species workers to begin rearing parasite-species workers. A pure parasite species colony eventually results because the host workers are not replaced.

Type 3: Slave-making ants found new colonies parasitically in a fashion similar to temporary parasites but replace the host workers by raiding other nearby host-species colonies and kidnapping brood from which additional slave workers are reared.

Type 4: Inquiline parasite queens secure adoption by host colonies which subsequently produce more inquiline-species reproductives. Usually, the host-species queens survive.

2. At the end of a SimLife experiment, what is the simplest way to determine what net evolutionary changes have occurred in a species? (6 points)

In the Biology Lab, execute the command to change the species prototype to match the population.

3. According to Axelrod and Hamilton's theory of co-operation, what conditions are conducive to the evolution of co-operation? (10 points)

Individual members of the population should encounter one another repeatedly, with the number of encounters for particular individuals being unpredictable.

4. Define an ESS. (10 points)

An ESS is a strategy which, once it has been adopted by every member of the population, cannot be bettered by any other strategy in the strategy set.

5. Below are two payoff matrixes for Hawk-Dove mixed ESSs. In these matrixes, V is the fruits of victory, C is the cost of defeat, and T is the cost of wasted time; and V, C, and T are measured in units of personal fitness.


The only difference between the two matrixes is the value of E(D,D).

In the top matrix, the proportion of Hawks in the population (p) will be: .

In the bottom matrix, the proportion of Hawks (p) will be: .

How does figuring in the cost of wasted time affect the proportion of Hawks in a population? (Hint: Just look at how it affects the proportions in the equations.) (8 points)

Figuring the effect of wasted time raises p.

What value(s) of p, if any, would indicate that Hawk an ESS? (Hint: Don't worry about what the computed values of p would be in the matrixes given above.) (8 points)

Hawk is an ESS if p > 1.

6. Imagine a species of eusocial Hymenoptera in which each colony has one queen, each queen mates with exactly one unrelated male, and no male mates with more than one queen. In this species, new queens are always the offspring of the colony queen, and males are always the offspring of a single worker in each colony. According to Dawkins, what ratios of investment in queens and males best fit the reproductive interests of the colony queen, the male-producing worker, and the other workers. Explain your answer. (How are these three kinds of individuals related to the new queens and males that the colony produces?) (12 points)

Individual(s) r to new queens r with males Preferred Ratio
Queen 0.5 0.25 2:1
Male-Producing worker 0.75 0.5 3:2
Other Workers 0.75 0.375 2:1

The preferred queen:male ratios of investment are proportional to the ratios of the relatedness (r) of the different kinds of individuals to the offspring reproductives that the colony produces. These values are given in the table above.

7. So far as we know, all social insects that are able to discriminate between members of their own colony and members of other colonies of the same species do so on the basis of non-volatile chemical cues located on the surface of the insects' bodies. These chemical cues may be produced by the insects themselves or derived from the environment. The most likely sources of environmental cues are food and nesting material

Imagine that you discover a new species of ant. You collect several colonies and bring them back to your lab, where you place them in identical plastic artificial nests and feed each colony exactly the same kind of food. After the ants have been in the lab for forty-eight hours, you perform a series tests in which a single worker is removed from each colony and introduced into the nest of another colony and find that in every case the introduced ant is attacked and killed. Three months later, you repeat the aggression test and find that the introduced ants are no longer attacked or killed. What do these results suggest about the source (or sources) of cues on which colony-member recognition is based in this species? Explain your answer. (10 points)

The fact that the colonies could distinguish themselves from one another at first but subsequently lost the capacity to do so suggests that nestmate recognition is based on environmental cues derived from nesting material and/or food. After prolonged exposure to identical nests and food, distinctive cues from the natural environment wear off and the ants lose the capacity to make the distinction.

8. What aspect of ESS theory has provided individual- or gene-level explanations of certain phenomena that have traditionally been explained on the basis of population- or even species-level selection? Elaborate your answer by giving one or two examples. (12 points) (Hint: These are characteristics that seem to be for the `good of the species.')

Conditional ESSs are an aspect of ESS theory which have provided the capacity to explain a number of phenomena that have traditionally been explained on a good-of-the-species basis in individual or gene selection terms. A conditional ESS typically prescribes two different kinds of behaviour, one to be followed when the organism wins a contest and another when the organism loses a contest.

For example, in the case of food competition, a conditional ESS would prescribe that the animal take the resource if it is socially dominant but retire without a fight if it is socially subordinate. Another example concerns territoriality and nesting in song birds. Each spring, rival mated couples compete for nest sites. The winners succeed in establishing nesting territories and rear young, while the losers retire peacefully and do not harass the breeding pairs.

9. One of Richard Dawkins' most interesting and controversial ideas is his concept of the "extended phenotype," in which a gene located in one animal finds its phenotypic expression in the physiology or behaviour of another animal. Describe some aspect of the behaviour of socially parasitic ants to which this concept might reasonably be applied. (12 points)

There are several possible examples, but the student only needs to give one. The key idea here is that a subject individual when under the influence of another animal performs an action that it would not ordinarily perform. The action will always favour the individual under whose influence the subject animal is acting, and it will be contrary to the interests of the actor.

When a parasite ant queen invades a host colony, the host workers often kill their own queens, an action which benefits the invading parasite to the host workers' detriment.

During slave-raids, slave workers join raiding parties by following pheromone trails laid down by the slavemakers even though unenslaved workers never follow pheromone trails.