PSY 252H - Introduction to Animal Behaviour

Professor Tom Alloway

Fall 1997 Second Term Test

1. Briefly describe the two major kinds of mating flights that occur in ants.

In mixed sex swarms, both sexes fly to the tallest objects in the local area where pair formation takes place. In queen-attraction flights, the queens leave their parental colony, perch on some nearby object, and emit a pheromone that attracts the males.

2. Colonies of the ant species Leptothorax species A can produce either or both of two kinds of reproductive females (queens): normal queens with deciduous wings and wingless ergotogynes. Both kinds of queens have a spermatheca. In queens of both types, both ovaries contain several ovarioles (tubes in which eggs develop). Thus, after mating both kinds of queens are capable of laying both fertilised and unfertilised eggs. In fact, virtually the only difference between normal queens and ergotogynes is that the ergotogynes never have wings or wing muscles. New L. species A colonies are generally formed by budding, a process that enables the species to permeate small, local areas of suitable habitat. However, lone queens also sometimes found new colonies in the typical claustral way. These lone foundresses are almost always normal queens. Apart from the obvious fact that the ability to fly is an advantage when looking for an appropriate nest site, what physiological advantage do the normal queens have over ergotogynes during colony foundation?

During claustral colony foundation, queens feed their first larvae a special "baby food" derived metabolically from the queen's wing muscles and fat body. Ergotogynes lack the wing muscles that are the principal source of protein for this larval food. Normal queens that have wing muscles are much better suited for claustral colony foundation.

3. Myrmica is a genus of ants found around the world in the North Temperate Zone. In this genus, the workers have ovaries in which eggs develop while they are pupae. During the first days of their adult lives, the workers lay these eggs. After that, the workers' ovaries atrophy and never function again. Throughout their adult lives, workers perform typical worker-ant functions (e.g. foraging for food, looking after the brood, building and guarding the nest). In contrast, the ovaries of queens become functional after they emerge as adults and remain functional throughout the rest of their lives. After the colony-foundation stage of colony development, a queen's only "job" is to produce eggs. As a consequence of this social system, most males that colonies produce are the offspring of workers, while the workers and queens are exclusively the offspring of queens. Are the species this genus eusocial? Explain your answer.

Yes, the species is eusocial. Eusocial species have reproductive division of labour, communal care of the young, and an overlap of generations. Worker-produced males do not alter any of these characteristics because only queens can produce female offspring.

4. What is an ESS?

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

5. After a queen of a certain species of workerless inquiline ant has successfully invaded a host colony, the host workers kill some of their own queens. What concept which Dawkins espouses would best explain this behaviour of the host workers? (Hint: Remember that the death of the host queens benefits the parasite queen at the expense of the genetic interests of the host workers.)

The concept that Dawkins invented to deal with this kind of situation is the extended phenotype, in which the phenotypic expression of a gene occurs in the body of another animal. The allele for queen assassination is in the parasite queen, but it is expressed by the host workers (perhaps as a reaction to a pheromone produced by the parasite).

6. What is the principle difference between a conditional ESS and the kind of mixed ESS in which the same individuals sometimes follow different strategies?

In the case of the mixed ESS, the "decision" about which strategic behaviour to manifest is random. In a conditional ESS, the decision is based on the evaluation of stimuli (called asymmetries) which the opponent produces.

7. Assume that the iterated Prisoners' Dilemma payoff matrix given below is in effect.

Remember the following long-term expected payoffs:

To TIT FOR TAT playing TIT FOR TAT:

To ALL D playing TIT FOR TAT:

To DC ALTERNATION playing TIT FOR TAT:

Under what conditions will TIT FOR TAT be an ESS against ALL D and DC ALTERNATION? Hint: Don't do any computations. Just write two equations.

TIT FOR TAT will be an ESS against ALL D if .

TIT FOR TAT will be an ESS against DC ALTERNATION if .

8. Name and in a very few words describe three of the game parameters that can be manipulated in the Change Physics window of SimLife.

Below is a screen shot of the SimLife Change Physics dialogue box, showing the parameters that can be manipulated.

9. In what ways does the meaning of the term strategy as used in ordinary English differ from the technical meaning of the term in ESS theory?

In everyday language, a strategy is a long-term plan for reaching a goal; and having such a plan implies conscious thought. In ESS theory, a strategy is simply a description of one of two or more different things that animals do in a particular kind of situation. In ESS theory, the term implies nothing about consciousness.

10. According to Dawkins, what is the must fundamental difference between males and females?

Males produce very large numbers of small gametes called sperms. Females produce comparatively fewer larger gametes called eggs.